Basics of Chemistry

Jason Moore
This is an introduction to the fundamental concepts of chemistry. This is ideally for those students just beginning with chemistry whether in high school or college. I am including basic concepts as well as some example problems.

Ankr Store on Amazon, keep your electronics charged by the best! If you buy something, I get a small commission and that makes it easier to keep on writing. Thank you in advance if you buy something.

 

Table of Contents

 

Basic Chemistry Concepts 

 

Matter is tangible. It is something that has mass and takes up space. You can also look at it as being physical in the sense that you can see, touch, or smell it. One of the parts of matter is mass. Mass is how much there is of it when measured. Of course taking up space means that it has some volume that you can also measure. Matter is then quantifiable which means you can also give it units when measured.
 

What is not Matter?

 

Things that are not matter include whatever you can not touch see, or hear. This means forms of energy, time, sound, and information. Forms of energy include gravitational, chemical, nuclear, and elastic, motion, thermal, sound, electromagnetic, and electric. That is quite a list and I could go in depth on each of those but I will save that for a later post.
 

Forms of Matter Around Us

 

The forms of matter are the well known solids, liquids and gases. Some types of matter stay in one category. Other types of matter can transition between the different forms. Solids have a certain size and shape that will not change on its own.
 
They are rigid. Its atoms are packed very close. Liquids are more variable than solids. They have a size and shape but that depends on its environment or what it is in to be precise.
 
That means it will take the shape of whatever container that holds it. Liquids have a characteristic that is called fluidity. This means the liquid will flow and take the shape of wherever it is. Solids do not flow.
 
The last type of matter is gases. They do not have a size and shape of their own. They will, however, take the shape of whatever they are in if the particles are not allowed to leave the container.
 
There is technically another state of matter called plasma but we will leave that for later as it is more advanced.
 

Physical Properties of Matter

 

Physical properties are one of the subjects that make chemistry interesting. Every substance has its own properties. The substances can then be classified according to their properties.
 
Common physical properties are mass, temperature, melting point, density, elasticity, magnetic, electrical, and color. There are more as well that are less common.
 
Properties can be further divided as to whether they are extensive or intensive. Extensive properties, like mass, depend on how much of the matter you have. Intensive properties, like color, do not depend on how much of the particular matter you have.
 
Pay attention to this as the more interesting basic chemistry concepts are derived from here.
 
 
 

Sample Problem 1-Converting Units

 

If a truck is driving 60 miles per hour at a particular instant of time, how fast it is driving in kilometers per hour?
 
First you think about the relationship between the 2 units or unit systems. The 2 units are miles and kilometers. The relationship between these 2 units is this:
 
 
\[ km= miles * 1.6 \]
 
 
That is your formula. Formulas like this can be looked up anywhere online or in the back of some books that deal with the subject. So to solve this you just use this relationship between the units.
 
 
\[ km=60 miles * 1.6 = 96 kilometers. \]
 
 
   So the truck is moving at 96 km per hour.
 
 
This is obviously a very simple problem. The reason I started with it is I wanted to say something about problems. Solving problems basically comes down to a few things. If you do those things right then solving problems becomes a lot easier.
 
  • understanding what the problem is asking for
  • figuring out the relationship between everything
  • setting the problem up correctly mathematically
 

Chemical Properties of Substances

 

The chemical property of a substance refers to its characteristics as it changes its chemical properties. Its attributes and properties are then measured again. You can then compare its properties from before it changed.
 
A lot of people do this because its so interesting to analyze different substances as they change. Examples of chemical properties are combustion level and flammability. This section is also very important in your foundation of basic chemistry concepts.
 

Forces

 

Force is a great concept to understand. Though most people would probably associate it with physics, it has applications in all the sciences. It is the push or pull on an object. Can change the motion of the object it acts on.
 
It can be extremely small such as on the atomic level or tremendous as in the cosmic forces that act on each other. Force can be measured too. Its units are the Newton. It is also considered a vector quantity.
 
It is directly related to Newton's 2nd Law of Motion. This Law states that when an object encounters a force it is accelerated. There acceleration obviously can be either positive or negative.
 
Depending on which way that goes it can increase the objects velocity or decrease it. The basic formula for force =mass * acceleration.
 
 
 

Sample Problem 2

What force does a 24 kg object have if it is accelerating at \( 6 m/s ^2 \) ?

So:  F = Mass * Acceleration

Plug in values: \( F = 24 kg * 6 m/s ^2 \)

Therefore: \( F = 144 N \)

 
 

Energy of Things

 

Energy is one of those words that is used all the time. Some people use it right but most do not. In chemistry it is the capacity to do work. You can not do any work if you don't have energy.
 
This may seem obvious when I put it like that but in problem solving many people tend to forget it. Its unit is the Joule. There are multiple types of energy too. They are kinetic, potential, and electromagnetic.
 
Kinetic energy comes from motion. Potential energy comes from its position before it undertakes any motion. There are 2 main types of potential energy which are gravitational and coulomb potential energy.
 
Electromagnetic energy is the energy created by an electric field. This is made up of oscillating electric and magnetic fields. 
 

Atoms

 

Societies have always tried to make smaller pieces of everything. Whether by cutting or burning or dissolving in a liquid, there have been those people that always try to go one step further.
 
Eventually we reached that limit and it is called the atom. This is the most basic and fundamental thing we know of today. It is one of the more important basic chemistry concepts. It is made up of particles which determine its make up.
 
They make up our elements that famously appear in the table of elements.
 
Nuclear Model

Atoms are made up of particles as mentioned above. These particles include the nucleus and electrons. The nucleus has a positive charge while the electrons have a negative charge.
 
The nucleus is held together by something called the strong force which is important to remember. The strong force is one of the basic forces of nature that hold everything together.
 
It holds together the particles of the nucleus. The atom as a whole is neutral, though, because the nucleus and electrons cancel each other out with their different charges.
 
The parts of the nucleus that have positive charges are called protons.  Protons are very small sub-atomic particles that are found in every atom. The number of protons determines what kind of atom or element you have.
 
An atom with 1 proton is hydrogen while an atom with 6 protons is called carbon. When you look at the periodic table this proton number is usually the top or main number you see.
 
That number is how many protons are in that element and that determines what the element is called.
 

Elements

 

Elements are substances that are pure of anything else. They can not be broken down further. One type of element will have the same number of protons every time. 
 
An element can be changed into another element but this requires nuclear fusion at the heart of stars for this process. The most abundant element in the universe is hydrogen by far. Everything else makes up the rest.
 

Isotopes

 

An atom can have different numbers of neutrons which will make the mass different. It could be less or more than the standard element. It is the same element but a slightly different substance and this is called an isotope.
 
So the number of neutrons will determine what isotope it is. Usually there are a few different isotopes for elements. There are not a lot of different isotopes for every element.
 
Each element is unique in that it has only special versions that it can change into and become an isotope. They will have basically the same properties as the original element.
 

Compounds

 

Compounds are elements that come together and combine. They are neutral in charge. They can be either organic or inorganic. Elements are then chemically joined.
 
They become something different. Compounds that form do so in a very defined manner. They do so in the same quantities the same every time.

 

 

Molecules

 

Another of the most influential basic chemistry concepts, there are huge areas to study of just molecules. Molecules are combinations of atoms in a specific order and makeup. Their structure is important and determines its attributes.
 
The electric charge of the molecule is also important as the makeup of its properties can depend on the charge. Molecules will also form chemical reactions.
 
Something important to remember is that all compounds are molecules but not every molecule is a compound.
 
 
 

Ions

 

Ions are atoms that gain or lose electrons. Usually not many at once but the effects are profound. Losing electrons gives the atom a positive charge while gaining electrons will then give it a negative charge.
 
The reasons is that electrons are negative in nature and gaining or losing is just adjusting the negative charge of an atom. Once these atoms lose an electron they can then be classified as either cations or anions.
 

Cations

 

A cation is just an ion(compound or molecule) with a positive charge. This means there are more protons then electrons.
 
 

Anions

 

An anion is just the opposite of a cation. It is a negative ion which means there are more electrons than protons.
 

Naming Positive Ionic Compounds

 

Naming compounds in a systematic way is very important. It makes them unique. You know exactly what is being referred to because the positive ion is listed first. The negative ion is next. It is now a monatomic element .
 
This means 1 atom. The charge is indicated after the name of the element. Ions that are polyatomic and positive should have -onium after their name.
 
 

Naming Negative Ionic Compounds

 

Ions that are negative and monatomic in nature will have the suffix -ide added. Now polyatomic negative ions are more complicated unfortunately. Here's the breakdown on how it works.
 
According to chemed.chem.purdue.edu, the name generally ends in -ate or -ite. The -ate suffix means there is a high oxidation state. The -ite suffix indicates a low oxidation state. The -hypo prefix is usually the lowest oxidation state.
 
The opposite is true of the -hyper prefix which means it has the highest oxidation state. To complicate things further, there are exceptions but not very many. These you will just have to learn as you come across them.
 
 
Chemistry, like all of the sciences, is a complex subject. This is just the beginning of what it takes to be proficient at it. You have to start somewhere though and that first step is always the hardest.
 
Get familiar with these concepts correctly and later concepts will be easier to pick up. Getting an understanding of the basic chemistry concepts for beginners is not hard to do.
 
It just takes a little effort. You will not regret it. Having a proper understanding of the big picture is important when trying to understand the details.
 

Fundamentals of Chemistry

Chemistry is extremely involved and difficult. People that attempt to study this in detail often do not know where to start. This is why I have put together this guide to just start on the fundamentals. More rigorous subjects are pursued afterwards.

Matter

In chemistry we concern ourselves with matter and how it changes forms. It is not easy to say what matter is though. The best way to think about it is that matter has mass and takes up space.

 

According to this definition, my bookshelf is matter but the light shining through my window is not. A substance is another term for matter but means pure and unadulterated matter.

Matter is a substance. It is made up of one thing . However, matter that is made up of many things, like concrete, is not a substance.

Substances can come in different forms. These different forms are the stats of matter. The usual states of matter that we talk about are a solid, liquid, and a gas. A solid is a rigid form of matter and is something we can handle.

The atoms are packed very closely in a solid. A liquid is a fluid that will have a surface when it settles. Their atoms are packed fairly closely but not as tightly as in a solid. Gases are another form of matter that are like a liquid but do not have a surface.

The atoms of a gas are very far apart.

Physical Properties

A physical property of any matter is its defining characteristic. This characteristic is something that we can measure or observe. When you measure the property of a substance you need to report the accuracy and precision of the data.

The precision of the data is the significant figures of the measurements.

Force

A force is something that changes the state of motion of an object. \(Force = mass * acceleration\).  This means there is a push or a pull on the object in question. Forces only have an effect when they are interacting with something else.

They can interact at a distance or when they contact something. Example of contact forces are tension, friction, and normal. Example of distance forces are gravitational, electric, and magnetic forces. Lastly, a force is a vector quantity.

This means the force has both a magnitude and a direction when applied and is one of the fundamentals of chemistry.

Energy

This is a term that most people are familiar with. They also have a vague sense of what it is. In chemistry it is important to understand that energy is transferred during reactions. That is the primary reason it is interesting to chemists.

In very simple terms energy is the capacity to do work. Work, applied to something, is motion of some sort.

There are 3 main types of energy. They are kinetic, potential, and electromagnetic. Kinetic energy is energy of motion and depends on how much work is done. Potential energy is that of position.

It depends on the forces involved and their magnitudes.   Electromagnetic energy is that of the electromagnetic field. Energy is carried through different mediums by waves.

Elements

There are well over a 100 different elements. Most are natural however a few are man made. At the most basic level an element is a substance that can not be broken down anymore using chemical methods.

The atoms of an element all have the same number of protons. They can have differing amounts of electrons though which give the elements different masses. When they have a different number of neutrons they are called isotopes.

Hydrogen and Helium are the most abundant elements that we know of. Many elements were discovered long ago. We do not know who discovered a lot of elements either.

Atoms

Atoms are very tiny particles and their study is one of the most important fundamentals of chemistry. In fact, they are so small that if we cut them in 2 then they would be something different at that point. We now know they make up our elements.

Compounds

A compound is a substance that is neutral in charge and is made up of two or more different elements. They are either organic or inorganic. Organic compounds all contain carbon. Inorganic compounds are everything else.

The elements in a compound are joined chemically. We call this being bonded together.

Molecules

There is always confusion between a compound and a molecule. A molecule is also neutral in charge like a regular compound. It is made up of more than one element.

However, a molecule can be made up of two of the same type of element. All these together are what makes a molecule.

The Mole

The mole is one of the man-made fundamentals of chemistry and is the main unit that chemists use in reporting data of their experiments. So what is a mole? A mole contains the same quantity of something that makes up the same in 12g of carbon-12.

So basically its the number of atoms in 12g of carbon-12. It is a lot of atoms for sure. Just like with any other number, however, we need to specify units or what exactly we are working with.

Molar Mass

The molar mass of an element is the mass per mole of its atoms. You have to use mass spectrometry to find the molar mass of elements. When the mass of an individual atom is large then that means the molar mass is greater also.

Since knowing the atomic weight of an element gives us an idea of the protons and neutrons we are then equipped to make a good guess about other properties.

Chemical Formulas

An empirical formula shows the relative numbers of atoms of each element present in the compound. This is important because it gives us the entire makeup of the compound.

For example, it will give us the ratios of elements in some substance. To get the formula you have to measure the mass of each element in the compound. This gives us the mass percentage composition.

\[ Element Percentage = \frac{Mass of Element}{Mass of Sample} * 100% \]

Molecular Formulas

To find the molecular formula of a sample we also need to have its molar mass. Of course we already know that we need to use a mass spectrometer to find the molar mass.

The molecular formula of a compound is found by determining how many empirical formulas units are needed to account for the measured molar mass of the compound.

Mixtures And Solutions

Most substances that we encounter in the world are not pure like an element. Just about everything we see and touch are mixtures of some sort. Mixtures of different compounds do not gain unique properties.

They are just varied quantities of multiples types of compound substances. Everything in a mixture retains its own properties. This is important to remember when you observe compounds and mixtures.

Obviously there are different types of mixtures. Mixtures that are not very uniform are called heterogeneous. This means that randomly taking a sample will not give us a true indicator of its composition.

Homogeneous mixtures vary in that they are completely uniform. Taking multiple samples will always give the same composition. You can also call a homogeneous mixture a solution.

Many every day products are solutions that we interact with on a regular basis.

The term dissolving means that we are producing a solution. This is commonly by mixing things together like my chocolate milk in the evenings.

When making a solution the more numerous parts are the solvent and the parts that get dissolved are the solute. In my chocolate milk example the milk is the solvent and the chocolate is the solute.

Chemical Reactions

Chemical reactions are around us every day. We can describe them in two parts, reactants and products. Reactants are what we start with and the product is what we end up with. Use firewood as an example.

The wood is our reactant and after we set it on fire we end up with ashes and those are our product.

We have learned that reactions do not lose mass in a controlled environment. This led chemists to the law of conservation of mass. This means that atoms are neither created or destroyed.

They just change forms. Equations that show a reaction can guide you through what happened to the quantities of everything is involved from starting point to the end product.

Chemical reactions are some of the most fun fundamentals of chemistry that I studied in school.

Aqueous Solutions

These are types of chemical reactions. An aqueous solution is when two different solutions are mixed and a chemical reaction takes place. This is not common but it does happen.

A soluble substance is one that dissolves to a significant extent in a specified solvent. An insoluble substance is one that does not dissolve significantly in a specified solvent.

A solute may be present as ions or as molecules. We can do a test on anything like this to determine which it is. The test is to see if the new solution conducts and electric current or not. If it does then it is ionic and if not it is molecular.

An electrolyte is a substance that is present as ions. ionic solids that are soluble in water are electrolytes because the ions become free to move when the solid dissolves.

The solute in an aqueous strong electrolyte solution is present as ions that can conduct electricity through the solvent. The solutes in nonelectrolyte solutions are present as molecules.

Only a small fraction of the solute molecules in weak electrolyte solutions are present as ions.

Precipitate Reactions

Some ionic compounds are soluble and others are not. In a precipitation reaction an insoluble solid product forms when we mix two electrolyte solutions. When an insoluble substance is formed in water it immediately precipitates.

A precipitation reaction takes place when solutions of two strong electrolytes are mixed and react to form an insoluble solid. These types of reactions and their study are some of the most popular of the fundamentals of chemistry

A complete ionic equation for a precipitation reaction shows all the dissolved ions. A complete ionic equation expresses a reaction in terms of the ions that are present in a solution.

A net ionic equation is the chemical equation that remains after the cancellation of the spectator ions.

Precipitation reactions will often make compounds. Chemists often plan this ahead of time to make certain things.

Acids and Bases

Substances that historically had sharp tastes were often associated with being an acid. If they were not acidic they were then termed as bases. We can easily tell the difference today with an instrument called a ph meter.

An acid is a compound that contains hydrogen and reacts with water to form hydrogen ions and gives away protons. A base is a compound that produces hydroxide ions in water and accepts protons.

When a molecule of an acid dissolves in water it donates a hydrogen ion to one of the water molecules and forms a hydronium ion. A substance that accepts an ion in a reaction is one that acts as a base.

Acids are molecules or ions that are proton donors. Bases are molecules or ions that are proton acceptors.

Strong acids are completely deprotonated in a solution while weak acids are not. Strong bases are also completely deprotonated in a solution while weak bases are not.

The reaction between an acid and a base is called a neutralization reaction. The ionic compound produced in the reaction is called a salt.

In the neutralization reaction between an acid and a metal hydroxide the cation of the salt is provided by the metal hydroxide and the anion is provided by the acid.

In a neutralization reaction that occurs in water, an acid reacts with a base to provide a salt. The net outcome of the reaction between between solutions of a strong acid and a strong base is the formation of water from hydrogen ions and hydroxide ions.

Redox Reactions

This is another type of reaction and it is very common. Oxidation and reduction are two types of redox reactions. What is common between these two subtypes is the loss of electrons and their transfer to another reactant.

We can often recognize the loss of electrons by noting the increase in charge afterwards. We can then infer that oxidation is electron loss and reduction is electron gain. Remember, however, that particles are never lost.

So, when anything is oxidized something else must be reduced. Oxidation is electron loss and reduction is electron gain and they both occur together in redox reactions.

We recognize redox reactions by nothing whether electrons have moved from one substance to another. Chemists keep track of electrons by using oxidation numbers. Oxidation means that an increase in its oxidation number has occurred.

Reduction means that a decrease in the oxidation number has happened. So a redox reaction is one in which there have been changes in the oxidation numbers.

The substance that causes oxidation is called the oxidation agent. When an oxidation agent reacts, it accepts the electrons released by whatever is being oxidized.

So the oxidizing agent in a redox reaction is whatever is being reduced and the reducing agent is what is being oxidized.

Stoichiometry

Stoichiometry is the process of predicting the amounts of reactant or product that will be needed for a given reaction.  You can tell this by balancing an equation which will give you the amounts of atoms involved. 

Of the fundamentals of chemistry that people learn, it can be a little confusing.

The balanced chemical equation for a reaction is used to set up the mole ratio which is a factor that is used to convert the amount of one substance into the amount of another substance.

In a mass to mass calculation, convert the given mass into moles, apply the mole to mole conversion factor to obtain the amount required, and finally convert the amount in moles into mass.

A common technique for determining the concentration of a solute is titration. This process is part of volumetric analysis. Titrations are usually either acid-base or redox reactions.

An acid-base is where an acid reacts with a base. A redox  titration is where the reaction is between a reducing agent and an oxidizing agent.

Limiting Reactants

The theoretical yield of a reaction is the max quantity of product that can be obtained from a given quantity of reactant. The percentage yield is the fraction of the theoretical yield actually produced.

\[ Percentage yield = \frac{actual yield}{theoretical yield} * 100% \]

The theoretical yield of a product is the max quantity that can be expected on the basis of the stoichiometry of a chemical equation. The percentage yield is the percentage of the theoretical yield actually produced.

The limiting reactant in a reaction is the reactant that governs the max yield of product.

The fundamentals of chemistry are quite complex and deep. In fact, we have not even got to the more fun parts yet.

That is the way it is though, you have to get these basic concepts down before the other things will make sense and you can really enjoy what chemistry has to offer.

 Beginning Atomic Theory

Two hundred years ago the fundamental discovery was that all elements are made up of atoms. Each sample of the same element had an identical atomic structure. This is what made each element distinctive.

You can always see a difference between one element and another. This is how we started identifying individual elements to catalog them and one of the first chemistry concepts to learn..

Compounds are formed when certain atoms are combined with each other. Any distinct compound will always have the same general number of atoms and ratios. Chemical reactions are changes in the way they are bound together.

An atom is mostly empty space that contains a very small nucleus in its center. Electrons move randomly around this nucleus far away from it. The nucleus has both protons and neutrons in it too.

To continue, a nucleus is very dense compared to the rest of the atom. It accounts for almost all of the atom's mass.

When atoms are combined, it is the electrons that join together in interesting ways. Their charges are very important in these interactions. The number of electrons that an atom contains directly influences its ability to interact with other atoms.

The greater amount of electrons increases its chances of joining with other atoms. This is one of the fundamentals of chemistry that is so interesting.

Chemical compounds are collections of different atoms. The force that holds a compound together is called a bond. Bonds are formed by the sharing of electrons. These chemical bonds are known as covalent bonds.

The compound that is formed by this process is a molecule.

Another type of chemical bond results from ions joining together. An ion is usually a group of atoms that has a distinct positive or negative charge. A bond is formed when an electron from one atom is stolen by another atom.

This is because of the charges I mentioned earlier. It is attracted to the atom.

This ion can be either positive or negative. A positive ion is called cation. The negative version is called an anion. As you can see, they have opposite charges. Opposite charges attract. The force of attraction between oppositely charged ions is called ionic bonding.


The Periodic Table


The periodic table can be very helpful in understanding the elements. The more you learn about chemistry, the more help it will be. The letters are the symbols for elements.

The number shown above each element is the atomic number of that element. This is the number of protons it has.

Most elements are metals. They all have relatively similar characteristics. Nonmetals are in the upper right of the table, except hydrogen, which is by itself in the top left.

Metals usually lose electrons to form positive ions. Nonmetals are the opposite and tend to gain electrons to form negative anions.

The table is arranged so that elements in the same columns have similar chemical properties.


Naming Compounds


Inorganic binary compounds are made up of two elements. They can be either ionic or covalent. Cations are always written first in the formula. Anions follow after. A cation with one type of atom takes its name from that element.

An anion with one type of element uses the first part of the element and then add "-ide" at the end. An example is fluoride.

I want to point out there is a lot more to naming compounds. You can have multiple types of atoms. Depending on what kind and the number, there are many more rules. For right now though, I just wanted to mention the very basics.



Atoms and their Internals


The electron was discovered first by J.J. Thomson. He found out that electrons had a charge and were everywhere. Electrons actually have a negative charge. Why don't atoms have a negative charge then?

That is because of the protons in atoms. They balance out the negative charge from an electron. There are also neutrons in an atom but they do not have a charge.

In the most popular model of an atom, all of the positive charge and most of the mass is centered in the nucleus. The negatively charged electrons are in varying spots around the nucleus. The atomic number of this object is the number of protons in the nucleus.


Atomic Radiation


The main way that atoms can be studied is by heating them up or applying a charge to them. When either of these are done the atoms will glow. Scientists study this light and its properties. This is the field of atomic spectroscopy.

Light is just another form of radiation. It moves very quickly. I am sure everyone has heard the term "speed of light". This is where its from. The important thing to remember about any form of radiation, is that it moves energy from one place to another.

Electromagnetic radiation moves as waves through a medium. As all waves do, they have an amplitude, intensity, and a wavelength. The amplitude is the height of the wave above the center.

The wavelength if the distance between peaks. The intensity of a wave is the square of its amplitude.

If the wavelength of a type of radiation is short then its frequency is high. Also, if the wavelength is long then the frequency will be low.


Spectrum of an Atom


Each type of wavelength has different characteristics. Distances and frequencies are all different from one another. This is the electromagnetic spectrum. This includes visible light, x-rays, radio waves, gamma rays, and ultraviolet.

All these types of radiation deserve their own area of study. Each has important roles. So in another point in time we will come back and take a look at them too.

Now we need to talk about equations. Math is fundamental to most subjects and this is no exception. The first one we need to be familiar with is the relationship between wavelength and frequency. It looks like this.

\[ wavelength * frequency = speed of light \]

This equates to the "c" constant that is always referenced when talking about the speed of light.

The next important equation concerns the spectral lines themselves. It contains the Rydberg constant after the famous person that discovered and put together this expression.

\[ v = R \left\{\frac{1}{n^2} - \frac{1}{n^2}\right\} \]

The Rydberg constant has been determined to have an exact value. It took many experiments to do but we have a nice consistent value for it now.

\[ R = 3.29 * 10^15 \]

When we send pure white light through an element we can see its spectrum. This looks like a bunch of black lines. The absorption lines have the same frequencies as the lines in the emission spectrum.

When you think about this it means that atoms can absorb radiation only of those certain frequencies. The takeaway is that an electron can only have certain energies.


Photons and Radiation


As mentioned before, when something is heated up a lot it will start to glow. Atoms, elements, and many other objects do this. This is known as incandescence. Its color will change depending on how high the temperature is. White is generally the hottest.

We now know that electromagnetic radiation is made up of particles. These particles are called photons. Each photon is a packet of energy and that energy is related to the frequency of the radiation.

Another important fact to remember is that the intensity is related to how many photons are present.

This leads us to the next important equation to be familiar with. It is Planck's constant.

\[ E = hv \]

The "h" is Planck's constant. It has a value of :

\[ h = 6.62 * 10^-34 \]

Assume electromagnetic radiation is a stream of constant photons. Meaning, they are a continuous. Therefore, the kinetic energy of electrons changes linearly with the frequency.

This tells us a few things. An electron can be driven away from a nucleus if a photon hits it with enough energy. If it does have enough energy, the electron that it hit will be ejected.

Finally, the energy of the electron increases linearly with the frequency of the radiation involved.

Studies of radiation led to Planck's idea of the quantization of electromagnetic radiation. The photoelectric effect provides evidence of the particulate nature of electromagnetic radiation.

In this chapter we talked about the basics of an atom and how we got there. Then we talked about the periodic table and the naming of compounds. After that we delved into the internals of the atom, specifically electrons and their properties.

 

Atomic Structures

The atom is the smallest unit of an element. It is made up of three different particles. They are:

  • Electrons
  • Protons
  • Neutrons

The combination of these particles are unique for each element. Each atom of the same element has the same combination of protons and electrons. An atom of helium on some faraway planet has the same combination of electrons and protons as one on Earth. 

 

Each element has a unique combination of protons and electrons in its atom. The combination of electrons and protons in an atom of one element is different from that in an atom of any other element. Since each element has a known number of protons and electrons, you can identify an element if you know these numbers. 

 

Protons

Protons are particles with a positive charge. Electrons are particles with a negative charge. Atoms have a neutral charge if they have the same number of electrons and protons. In any neutral atom, the number of electrons is always equal to the number of protons. Each element has a unique number of electrons and protons in its atoms. We can identify any element if we know either the number of protons or the number of electrons. 

 

Periodic Table

The periodic table describes the atoms of every element. For every listed element, the number of protons is listed at the top and the atomic weight is listed at the bottom. The number of protons in an element is known as its atomic number. 

 

Niels Bohr came up with an atomic model that pictured an atom with a nucleus of protons in the center and electrons spinning in an orbit around it. The model helps us remember and picture the details of an atom. The electron always has a negative charge. A proton carries a charge opposite that of an electron, which is positive. 

 

Electrons

An electron has very little mass compared to a proton. It takes around 1836 electrons to equal the weight of just one proton. In any atom, most of the weight is through the proton. However, the weight of an atom is not just protons and electrons. The other particle, neutrons, make up the rest. Neutrons are located in the nucleus along with protons. Neutrons can be found in most atoms of elements. 

 

In the periodic table, each element is represented by a one or two letter symbol. These symbols serve as a shorthand notation for the elements. The shorthand notation for each case represents a neutral atom. The periodic table of elements is made up of several rows and columns. The rows are called periods and the columns are called groups. Groups are often called families because the elements that make up the groups have similar chemical properties. 

The groups have names that identify them.

  • Group VIIIA = Noble gases
  • Group IA = alkali metals
  • Group IIa = alkaline earth metals
  • Group VIIA = halogens

 

The periodic table can also be divided into three categories. These are:

  • Metals
  • Nonmetals
  • Metalloids

Elements to the left of the stairs on the periodic table are called metals. Metals have certain properties. It is what makes them metals. Metals are:

  • Malleable
  • Ductile

Malleable means they can be beaten into fine sheets like gold. Being ductile means they can be drawn into wires. Metals are also good conductors of heat. They usually have a shiny surface. Most metals are solid at room temperatures. 

 

Nonmetals are located on the right side of the stairs on the periodic table. These are halogens and noble gases. Their properties are almost opposite that of metals. They are usually brittle and do not conduct electricity or heat. Nonmetals are usually gases at room temperature. 

 

The last category is called metalloid. They are a hybrid of the other two categories of elements. That means they have properties of both metals and nonmetals. 

 

Mass and mass Number

When looking at an element on the periodic table, the top number is the atomic number of the element and is also the number of protons in an atom of this element. The atomic number is often written as a subscript preceding an element’s symbol. The symbol and number \(_7 N\) indicate nitrogen with atomic number 7. 

 

Almost all of the mass of an atom is attributed to the nucleus. The nucleus is made up mostly of protons and neutrons. Mass is a measure of the amount of matter. The mass of an object determines its weight. Weight is the effect of gravity on mass. 

 

Adding together the number of protons and neutrons in the nucleus of an atom results in what is known as the mass number of the atom. The mass number is simply the number of protons added to the number of neutrons in an atom.  By convention, the mass number is often written as a superscript in front of the element symbol. 

 

The quantum atomic model of an atom uses the term shells to divide up an atom. Shells are numbered 1-7. Subshells are part of each shell. They are labeled s, p, d, and f for each shell. 

  • S subshell has a size of one
  • P subshell has a size of three
  • D subshell has a size of five
  • F subshell has a size of seven

Each compartment in a subshell is called an orbital. 

 

Electrons prefer the lower shells and the smaller subshells. Electrons will fill shells and subshells in this order:

  • 1s
  • 2s
  • 2p
  • 3s
  • 3p
  • 4s
  • 3d
  • 4p
  • 5s
  • 4d
  • 5p
  • 6s
  • 4f
  • 5d
  • 6p
  • 7s
  • 5f
  • 6d

This is called the electron configuration of an atom. We can also identify an atom if given its electron configuration. Remember, only one electron will occupy an orbital in a given subshell until all the orbitals in that subshell have one electron in them. Electrons occupy as many orbitals as possible in the same subshell before pairing with another electron. This is called the principle of maximum multiplicity. 

 

Each group of elements in the periodic table has similar subshells with similar numbers of electrons in the outermost shell. The outermost shell consists of the subshells that are filled last. This situation serves to explain the similar chemical properties of elements within the same groups. 

Atomic Weights in Chemistry

Intro
Each atom has a definite and characteristic weight. This weight provides a way
to state the amount of a substance required for a chemical reaction.

Example 1
The notation \({^{35}_{17}Cl}\) indicates a neutral atom of chlorine.
1. What is its atomic number? 17
2. What is its mass number? 35
3. How many protons does it have? 17
4. How many electrons? 17
5. How many neutrons? 18

Example 2
Different atoms of the same element can have different numbers of neutrons and,
therefore, different mass numbers. Here is another neutral chlorine atom.
\({^{37}_{17}Cl}\)
1. What is its mass number? 37
2. How many protons does it have? 17
3. How many neutrons? 20

Example 3
Since neutrons and protons combine to make up the mass number, two atoms of the
same element can have different mass numbers. Chlorine can exist  as
\({^{37}_{17}Cl}\) and as \({^{35}_{17}Cl}\). The only difference between
these atoms of chlorine is that \({^{37}_{17}C}\) has two more neutrons than
\({^{35}_{15}Cl}\). Antimony can exist as \({^{121}_{51}Sb}\) and
\({^{123}_{51}Sb}\). The only difference between these atoms of antimony is
that \({^{123}_{51}Sb}\) contains two more neutrons than
\({^{121}_{51}Sb}\).

Example 4
\({^{37}_{17}Cl}\) has a greater mass than \({^{35}_{17}Cl}\) because of
the two extra neutrons. Which of the following atoms of antimony has the greater
mass, \({^{121}_{51}Sb}\) or \({^{123}_{51}Sb}\)? \({^{123}_{51}Sb}\)
does because it has two more neutrons.

Example 5
Atoms of the same element having different masses are called isotopes. Elements
as found in nature are usually mixtures of two or more isotopes. The atom
\({^{123}_{51}Sb}\) is one isotope of the element antimony.
\({^{121}_{51}Sb}\) is another isotope of antimony. The main difference
between two isotopes of the same element is the number of neutrons.

Example 6
Isotopes exist for every known element. The isotopes of the element neon were
first discovered by two English scientists. They continued in their work to
discover other isotopes through inventing the mass spectrograph or spectrometer.
In the mass spectrograph, atoms of different masses of the same element are charged and accelerated by an electron beam toward a target, such as a
photographic plate. A strong magnetic field bends the paths of the charged
atoms. Atoms of greater mass have their paths bent to a lesser degree than atoms
of lighter mass. 
In the diagram of the mass spectrograph pictured, where do the
lighter atoms strike? The higher point A because the path of the lighter atoms
is bent to a greater degree.

Example 7
An analogy to the mass spectrograph would be to roll a bowling ball and a
basketball at the same speed at a target while a stiff crosswind is blowing. The
bowling ball is considerably heavier than a basketball. Look at the diagram
below. Which ball would strike the target at point B?
The basketball because it is lighter and its path is more readily changed by the
crosswind. 

Example 8
In the rolling balls analogy to the spectrograph, the bowling ball and
basketball are analogous to isotopes of different mass. The strong crosswind is
analogous to the? magnetic field

Example 9
Thomson and Aston invented an instrument that detects the presence and
characteristics of isotopes. What is this instrument called?
mass spectrograph or spectrometer

Example 10
The atomic weights of the elements are listed in the periodic table. The atomic
weight of sodium, for example, is listed as 22.990. The atomic weight listed for
sodium is actually the atomic weight of a mixture of isotopes,
\({^{22}_{11}Na}\) and \({^{23}_{11}Na}\). The proportion of these
isotopes is generally constant wherever sodium is found. 
The atomic weight of an element is the average weight of a mixture of two or
more?
isotopes

Example 11
The periodic table lists the atomic weight of Al as?
26.982

Example 12
Atomic weights are based on the carbon 12 scale. That is, carbon 12 or
\({^{12}_{6}C}\), the most abundant isotope of carbon, is used as the
standard unit  in measuring atomic weights. By international standard, one atom
of the \({^{12}_{6}C}\) isotope has an atomic weight of exactly 12 atomic
mass units, abbreviated amu. The atomic weight of the \({^{12}_{6}C}\)
isotope is exactly?
12 amu

Example 13
All atomic weights can be expressed in atomic mass units. By international
agreement, 12 amu would equal the mass of a single \({^{12}_{6}C}\) atom. One
amu is equal to what fraction of a single \({^{12}_{6}C}\) atom?
1/12 the mass of a single \({^{12}_{6}C}\) atom

Example 14
Although the \({^{12}_{6}C}\) isotope weights exactly 12.000 amu by
definition, the atomic weight of C as listed on the periodic table is 12.011
amu. The atomic weight of carbon as listed on the periodic table is greater than
that of the \({^{12}_{6}C}\) isotope. Why?
The atomic weight of an element is the average weight of a mixture of two or
more isotopes.

Example 15
While the element carbon as found in nature is made up largely of the
\({^{12}_{6}C}\) isotope (98.9%), a small quantity of \({^{13}_{6}C}\)
isotope (1.1%) is mixed uniformly as part of the element. The \({^{12}_{6}C}\)
isotope has an atomic weight of 12.000 amu. The \({^{13}_{6}C}\) isotope has
an atomic weight of 13.003 amu. The resultant average atomic weight would be
slightly (heavier, lighter) than 12.000 amu?
Heavier.

Example 16
The atomic weights on the periodic table are the average atomic weights of the
isotope mixtures in the element. We can determine the average atomic weight of
an element if we know the approximate mass of each isotope and the proportion of
each isotope within the element.

Here are the steps for calculating the average atomic weight of the element
carbon. 
1. Multiply the mass of the \({^{12}_{6}C}\) isotope by its decimal
proportion (12.000*0.989).
2. Multiple the mass of the \({^{13}_{6}C}\) isotope by its decimal
proportion (13.003*0.011).
Add the results to find the average atomic weight of the element C.
You should get 12.011 or 12.01 rounded.

Example 17
Calculate the atomic weight of fluorine.
For the \({^{19}_{9}F}\) fluorine isotope, with a mass of 19.000 and
proportion of 0.997, we have: 18.943
For the \({^{18}_{9}F}\) isotope, with a mass of 18.000 and proportion of
0.003, we get: 0.054
added together, we get: 18.997 or 19.00

Example 18
Sodium has two isotopes, \({^{23}_{11}Na}\) and \({^{22}_{11}Na}\). The
isotope \({^{23}_{11}Na}\) has an atomic mass of approximately 23.000 amu,
and its proportion in the element is 99.2%. The isotope \({^{22}_{11}Na}\)
has a mass of approximately 22.000 amu and a proportion within the element of
0.8%. Determine the atomic weight of sodium.
\(23.000   *   .992   =22.816\)
\(22.000   *   .008   =.176\)
Add the totals together to get:
\(22.99\text{ amu }\)

Example 19
The element cobalt has an isotope \({^{60}_{27}Co}\) that has an approximate
mass of 60.000 and constitutes 48.0% of the element. Another isotope
\({^{58}_{27}Co}\), has an approximate mass of 58.000 and constitutes 52.0%
of the element. Calculate the atomic weight of Co using the given data.
\(60.000   *   .48   =28.8\)
\(58.000   *   .52   =30.16\)
Add the totals together to get:
\(58.96 \text{ amu }\)

Example 20
The percentage proportions of all the isotopes within an element must add up to
a total of 100%. The decimal proportions of all the isotopes within an element
must add up to 1.

Example 21
We have been calculating atomic weight given the mass and proportion of
isotopes. We can also determine the proportion of each individual isotope within
an element if we know the atomic weight of the element. The element Cr, which
has an overall atomic weight of 51.996 amu, has two isotopes:
\({^{52}_{24}Cr}\) with atomic mass of 52.000 amu and \({^{51}_{24}Cr}\)
with an atomic mass of 51.000 amu. 
We are given the sum as \(51.996\)
We do not know the proportions of either yet.

Example 22
To solve this equation with two unknowns, you must form a second equation
showing the relationship between A and B. You have already learned the answer to
the following question in example 20. Add the decimal proportions.
A+B=1

Example 23
Modify the equation in example 22 so that just B remains on the left side of the
equation. 
B=1-A

Example 24
Here is the equation you need for calculating the sum of the isotopes
mass * proportions: (52.000A)+(51.000B)=51.996. Substitute the expression (1-A)
for B in the equation:
\(52.000A+51.000(1-A)=51.996\)

Example 25
Solve the equation derived in example 24 to determine the value of A (the
proportion of \({^{52}_{24}Cr}\) in an average mixture of chromium) to the
nearest thousandth. 
\(52.000A+51.000(1-A)=51.996\)
\(52.000A+51.000-51.000A=51.996\)
\(1.000A+51.000=51.996\)
\(1.000=.996\)
\(A=.996\)

Example 26
Since B=1-A, what is the value of B?
\(B=1-A\)
\(B=1-.996\)
\(b=.004\)

Example 27
Here is a similar problem. In the next few examples, you will determine the
proportion of the \({^{35}_{17}Cl}\) isotope in an average mixture of
chlorine, which is made up of both \({^{35}_{17}Cl}\) and
\({^{37}_{17}Cl}\).
\(34.97   *   A   =34.97*A\)
\(36.97   *   B   =36.97*B\)
The values of A and B added together equal?
1

Example 28
Since A and B=1, then B=?
\(1-A\)

Example 29
The proportion \(1-A\) has been substituted for B.
\(34.97   *   A   =34.97A\)
\(36.97   *   B   =36.97B\)
Added together is \(35.45\)
Using the table above, determine the proportion of \({^{35}_{17}Cl}\) within
the element chlorine (find the value of A). 
\(34.97A+36.97(1-A)=35.45\)
\(34.97A+36.97-36.97A=35.45\)
\(36.97-2.00A=35.45\)
\(36.97=35.45+2.00A\)
\(1.52=2.00A\)
\(A=.76\)

Example 30
Determine the proportion of \({^{37}_{17}Cl}\) in Cl.
The proportion has been given the value of B.
\(B=1-A\)
\(B=1-.76\)
\(B=.24\)

Example 31
Neon has two isotopes: \({^{22}_{10}Ne}\) and \({^{20}_{10}Ne}\). The
approximate mass of \({^{22}_{10}Ne}\) is 22.000 and the mass of
\({^{20}_{10}Ne}\) is approximately 20.000 amu. The atomic weight of neon is
20.179 amu. Determine the proportion of the \({^{22}_{10}Ne}\) isotope within
the element. 
\(22.000A+20.000B=20.179\)
\(B=1-A\)
\(22.000A+20.000(1-A)=20.179\)
\(22.000A+20.000-20.000A=20.179\)
\(2.000A+20.000=20.179\)
\(2.000A=.179\)
\(A=.090\)

Example 32
What is the proportion of the other isotope, \({^{20}_{10}Ne}\), within the
element?
\(B=1-A\)
\(B=1-.090\)
\(B=.910\)

Example 33
So far, we have considered all atomic weights in terms of atomic mass units.
1. An atomic weight expressed in amu represents the average weight of how many
atoms of an element?
1. An atomic weight expressed in amu represents the average weight of one single
atom of an element.
2. Carbon has an atomic weight of 12.011 amu, which represents the average
weight of how many atoms of carbon?
1

Example 34
Since it is impossible to measure the weight of one atom with a laboratory
balance, another unit for expressing atomic weight must be used. Atomic weight
can be expressed in grams as well as amu. An atomic weight expressed in grams
contains \(6.022*10^{23}\) atoms. This number, called Avogadro's number, will be
encountered often.
1. If the atomic weight of carbon is expressed as 12.011 amu, it represents the
average weight of how many atoms?
one
2. If the atomic weight of carbon is expressed as 12.011 grams, it represents
the average weight of how many atoms?
\(6.022*10^{23}\)

Example 35
Using information in example 34. answer the following question. One gram is how
many times heavier than 1 amu?
\(6.022*10^{23}\)

Example 36
One ton is equivalent to 2000 pounds. One pound represents 1/2000 of a ton.
\(6.022*10^{23}\) amu is equivalent to 1 gram. One amu represents what fraction of
a gram?
\(\frac{1}{6.022*10^{23}}\)

Example 37
Avogadro's number \(6.022*10^{23}\) is written in exponential notation. It
actually represents a very large number. Exponential notation will be used
often. The exponent indicates the number of places that the decimal must be
moved. The number 645,000 has the decimal moved five places to the left. The
result is \(6.45*10^{-5}\). 

To divide two numbers with exponential notation, divide the decimal portions of
the numbers and subtract the exponent in the denominator from the exponent in
the numerator.

Example 38
Unit Factor Analysis
If the problems in earlier example had been more difficult, we would have used
the unit factor method (called factor label analysis and dimensional analysis)
for solving problems.

The unit factor method involves multiplying the given value by one or more
conversion factors.

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