Download Hi Guys. Today we are going to be talking about the smallest part of

Hi Guys. Today we are going to be talking about the smallest part of matter. The smallest part of matter
is the atom. Atoms have two basic parts. They have a central nucleus. The nucleus of an atom has
positives and neutral charges. The positive charges are called protons. The neutral charges are called
neutrons. Because the nucleus has positive protons and the neutrons don’t have a charge, the overall
charge of the nucleus is going to be positive, so the nucleus is positively charged. Remember that
opposites attract, so negative charges are going to be attracted to the positively charged nucleus.
Negative charges are surrounding the nucleus in what are called energy levels, electron clouds, or
orbitals. These are going to be your electrons. So, electrons have a negative charge and they are found
surrounding the nucleus. It is important for you to remember the general structure of an atom with the
nucleus and then the electron cloud, energy level or orbitals that are surrounding the nucleus. You
should also know the three subatomic particles: protons, neutrons, and electrons and you should know
the charges of each of these subatomic particles. Protons have a positive charge. You can remember P
protons, P positive. Neutrons are neutral. They have no charge. And electrons are negative. So these
are the three subatomic particles of an atom.
In lesson 2, you are going to be learning more about the periodic table of elements, but you need to go
ahead and become familiar with the periodic table, because the periodic table is going to help you with
lesson 1 as well. There is a lot of information on the periodic table that is going to help you
understanding the structure of an atom. So let’s take a look at the periodic table and let’s take a look at
the first element on the periodic table which is hydrogen. You are going to notice a bunch of boxes on
the periodic table and the boxes are going to have a letter inside. This letter is the chemical symbol and
the chemical symbol is the letter that represents that element. So, the chemical symbol for hydrogen is
H. Above and below the chemical symbol you are going to notice some numbers. These numbers are
going to tell you a lot about the atom. Above the chemical symbol you are going to notice a number.
This number is going to be the atomic number. The atomic number is important because it tells us the
number of protons, the number of positive charges and the number of electrons. The number of
protons and electrons is the same. Because it is the same, the number of positive charges and the
number of negative charges are going to cancel out. So for hydrogen, hydrogen has 1 positive charge
and 1 negative charge. The positive and negative charge cancel out so overall the charge of hydrogen is
nothing. It is going to be neutral. The atoms on the periodic table as they are on the periodic table are
going to be neutral having no charge. We’ll talk more about positively and negatively charged atoms in
a minute. For right now let’s keep it simple and hydrogen here is going to be neutral. It is going to have
the same number of protons and electrons. And that atomic number is going to tell me how many
protons and electrons it has. Remember that protons are found within the nucleus of an atom. So if I
were to draw the hydrogen atom, inside the nucleus I would have the protons and in the case of
hydrogen I would have 1 positive charge. Surrounding the nucleus remember in your energy levels,
orbitals, or electron clouds, have a lot of different names, surrounding the nucleus you are going to have
electrons. Hydrogen has 1 electron so for the first energy level hydrogen is going to have 1 electron.
And I am going to represent that electron by doing a dot. So this first circle would be the first energy
level and I would put one dot. The first energy level can hold up to two electrons, but hydrogen only has
1 so I’m just going to put one dot to represent that 1 electron. So, so far, I know that from this atomic
number, I have one proton and one electron. And the charges cancel out so this is going to be a neutral
atom. Below the chemical symbol you are going to notice another number. For hydrogen it is 1.00794.
That number is the atomic mass. Compared to protons and neutrons, electrons don’t really have a
significant mass that contributes to the overall mass of the atom. So when we are talking about the
atomic mass, we are really talking about the mass of the protons plus the neutrons. One of the things
you can do is round the atomic mass to make it easier for yourself. So so far I know that I have one
proton and one electron from the atomic number. How am I going to figure out how many neutrons I
have? Well, the atomic mass tells me how many protons plus neutrons. And I am going to round it, so I
am going to say that the atomic mass of hydrogen here is 1 so if I take the atomic mass minus the
atomic number, which is the number of protons, I’m going to get the number of neutrons. So this is
how you can figure the number of neutrons an atom has. You are going to take the atomic mass minus
the atomic number because that represents the number of protons and that is going to give you the
overall number of neutrons. So if you take the atomic mass rounded minus the atomic number, you get
the number of neutrons. So I am going to have zero neutral charges here. This is what a hydrogen
atom looks like. When we draw an atom out like this, like I’ve done here, showing the number of
positive and neutral charges within a nucleus and the number of electrons in the energy levels this is
what we call a Bohr Model.
Ok, so we just drew the Bohr Model for hydrogen. Let’s take a look at another element on the periodic
table. Find oxygen on the periodic table. Oxygen is going to be number 8 on the periodic table. It has a
chemical symbol O. Above that chemical symbol you are going to see the number 8 which represents
the atomic number and below you are going to see 15.9994 which represents the atomic mass. The
atomic number again tells us how many protons and how many electrons we have. The atomic mass is
going to tell us the number of protons plus the number of neutrons. If I were to ask you how many
protons oxygen has, you would say 8 because the atomic number tells us the number of protons.
Remember that atoms are neutral and they don’t have an overall charge. So because it has 8 positive
charges, it is also going to have 8 negative charges, so it has 8 electrons. To figure out how many
neutrons it has, you need to take the atomic mass minus the atomic number, so we are going to round
the atomic mass to 16 and take 16 minus 8 and we are going to get 8 neutrons. So, now let’s go ahead
and do our Bohr model. We know that our atom has a nucleus and inside the nucleus we find our
protons. For oxygen we have 8 protons. We also find our neutrons so we have 8 neutrons. Surrounding
our positively charged nucleus we have 8 electrons in our energy levels. The first energy level can hold
a maximum of 2 electrons, so I am going to go ahead and put two dots in this first energy level.
Remember that oxygen has 8 electrons, so if you take 8 minus 2 you are left over with six electrons. The
second energy level can hold up to 8 electrons, so I have two in the first and I’m left over with 6. I am
going to draw 6 electrons in my outer energy level.
Let’s take a look at a couple more examples. Find sodium on the periodic table. Sodium is number 11
on the periodic table and has a symbol of Na. That 11 again the atomic number tells me that I have 11
protons and I also have 11 electrons. So the overall charge of sodium is going to zero, no charge,
because the positives are going to cancel out the negatives because I have the same number of protons
and electrons. The atomic mass for sodium is 22.989779. I am going to go ahead and round that to 23.
That atomic mass tells me again the number of protons plus the number of neutrons. So to figure out
how many neutrons I have I take the atomic mass of 23 minus the atomic number of 11 and I get 12.
Drawing the diagram again we have the nucleus with our positives 11 protons here and our neutral
charges and then surrounding this positively charged nucleus we have our electrons. Sodium has 11
electrons. Remember that only 2 electrons can fit in the first energy level that leaves me with 9. The
maximum for the second energy level is 8. So I have to go ahead and add a third energy level. So
sodium has one outer electron. This outer electron is called a valence electron. Valence electrons are
going to be important especially when we talk about how atoms and elements interact with each other
and when we talk about their reactivity – how likely they are to react with another. So sodium has 1
outer electron, 1 valence electron. Something else you are going to need to be familiar with, you are
also going to need to know how to do a dot diagram from all of these elements from hydrogen to argon.
So in addition to doing the Bohr model, you should also know how to do the dot diagrams. So for
sodium, the dot diagram is going to be Na for the chemical symbol and your dot diagrams again use the
chemical symbol as well as dots to represent the electrons in the outer energy level so sodium is going
to have 1 dot because it has 1 electron in its outer energy level.
Now let’s take a look at chlorine. Chlorine on the periodic table is Cl. The atomic number is 17 and the
atomic mass is 35.4527. Let’s go ahead and round that to 35. So for chlorine I have 17 protons. I have
17 electrons. And my neutrons I am going to find by taking my atomic mass minus my atomic number
so I have 18 neutrons. To draw my Bohr diagram, start off with the nucleus. Inside the nucleus you have
your positives and you have your neutrons which have no charge. Surrounding you are going to have
your energy levels. First energy level I have 2 electrons. Because chlorine has 17 electrons I am left with
15. Second energy level I can have up to 8 and then in the third energy level I am left with 7. So taking a
look at this Bohr diagram I have a total of 2 plus 8 that’s 10 and then 7 electrons in my outer energy
level. So chlorine is going to have 7 valence electrons. To do the dot diagram use the chemical symbol
Cl so I am going to do 2, 4, 6, 7 electrons here.
Do you guys remember that I said that atoms have no overall charge? They are neutral because they
have the same number of protons as electrons. Sometimes atoms can have a charge. An atom with a
positive or negative charge is called an ion. So an ion is any atom with a positive or negative charge.
Normally the atoms on the periodic table do not have charges because they have the same number of
protons as they do electrons. Later you are going to be learning about the reactivity of these atoms of
these elements and how they combine with one another to form compounds. So let me give you an
example of two elements that combine with one another or react with one another. Sodium and
chlorine. Sodium and chlorine can come together to form NaCl. NaCl is sodium chloride, also known as
table salt. The reason why sodium and chlorine come together and you are going to learn more about
this later is because of their valence electrons and how many valence electrons each has. Sodium only
has 1 valence electron. Chlorine has 7 valence electrons or outer electrons. And you can tell from their
dot diagram how many valence electrons or outer electrons they have. So sodium here has 1 outer
electron and chlorine has 7. I’ll go ahead and tell you this, but again you are going to be learning more
about it later. Atoms want to be happy and in order to be happy, they want their outer energy levels
filled. So for sodium it only has 1 outer energy level 1 electron in its outer energy level so to be filled it
either has to get rid of this one or has to gain 7 more. What do you think is easier for sodium to do? It is
easier for sodium to lose and electron. If sodium loses an electron it is no longer a neutral charged
atom, because sodium normally has 11 electrons. If it loses one it now only has 10 so that means that
sodium has more protons than it does electrons that makes sodium positive. So if sodium gives up this
electron it has a positive charge because it gave up some of its negative making it more positive.
Chlorine has 7 outer electrons and remember to be happy atoms want their outer energy level to be
filled so to be full chlorine only needs to gain 1 more electron. If chlorine gains an electron it is gaining a
negative charge. So if it takes on another electron to be happy, to have its outer energy level filled it
becomes a chlorine atom with a negative charge because it gains a negative. So normally again atoms
are neutral because protons and electrons equal each other, but sometimes when they react, they can
give up or take electrons. If they give up electrons they become more positive because they are giving
away some negative charge. If they take electrons they are becoming more negative. Again an ion is an
atom that has a charge.
We just talked about ions. Ions have a positive or negative charge because they have taken on or given
up electrons. So when they take more electrons or give up electrons they become positively or
negatively charged. An isotope is an atom of the same element that differs in the number of neutrons.
So let’s take a look at one of the elements that you should be familiar with and let’s talk about isotopes.
Carbon. Carbon is number 6 on the periodic table. Carbon has 6 electrons and 6 protons. If you take a
look at the atomic mass for carbon, you’ll notice that the atomic mass for carbon is not just 12. The
atomic mass is 12.0107. The atomic mass again tells us the number of protons plus the number of
neutrons. Why is the atomic mass for our elements so messy. Why is it not just 12. The reason for this
is because the atomic mass is really the average mass of all of the isotopes. Electrons again don’t have
much mass compared to protons and neutrons. So when we are talking about the atomic mass, we are
talking about the positively charged protons and neutral neutrons found in the nucleus. So the atomic
mass is really the mass of the nucleus. But because we can have variations of an atom, for example,
carbon. Carbon sometimes has 6 neutrons sometimes it can have 7 or 8. The atomic mass is going to be
the average of all of the variations of the carbon atom. That is why it is not just 12. So this 12.0107
represents the average for the atomic masses for carbon 12 and the atomic masses for carbon that has 7
or 8 neutrons. So let’s draw the Bohr diagram for carbon. Carbon has 6 protons. It has 6 electrons.
Rounded atomic mass to 12 and we would say that carbon has 6 neutrons. 12 minus 6. Draw this out, 6
positive charges in our nucleus and 6 protons. We have 2 electrons in our first energy level, 4 electrons
in our outer energy level. Fort the Lewis dot diagram C and then 4 dots surrounding it. So this is our
typical carbon atom. Our typical carbon atom we call C-12 or carbon 12 or another way to write this is
by putting the symbol C and then 12 and 6. 12 representing the atomic mass and the 6 representing the
atomic number. So these are some different ways you can write this carbon 12 isotope. Let’s take a
look at a different variation of carbon. You might also hear of carbon 14. Carbon 14 does not have 6
neutrons. It still has 6 protons and 6 electrons. But carbon 14 actually has 8 neutrons. So if I were to
draw the Bohr model for carbon 14 I would still have 6 positives, 6 protons, but now I would have 8
neutrons and then in my energy levels I would still have 6 electrons. To write carbon 14 I can put C-14,
carbon-14, or I can put C 14 and then the atomic number. So another way to write your isotopes is to
put the chemical symbol and then up here put the atomic mass and then down here you are going to be
putting the atomic number. So isotopes again are atoms of the same element that differ in the number
of neutrons.
You should go ahead and practice doing your dot diagrams and Bohr structures for all of the elements
from hydrogen to argon. Since argon is the last one, let’s go ahead and practice the dot diagram and
Bohr structure together. Argon has an atomic number of 18 and an atomic mass of let’s go ahead and
say rounded it is going to be 40. That means it has 18 protons, 18 electrons, and it is going to have 22
neutrons. So drawing my Bohr diagram I am going to put my positive and neutral charges in my nucleus
so 16 positives and 22 neutral charges and then filling in your electrons. Remember that your first
energy level can hold a maximum of 2. So it has a total of 18 and now minus 2 I have 16. Second energy
level can have a max of 8. So now I have a total of 10 so 18 minus 10 I’m left with 8 more. So the first
energy level again can have a maximum of 2 electrons. The second energy level can have a maximum of
8 electrons. The third energy level can also have a maximum of 8 electrons. Once you get past the third
energy level, electrons start bouncing around making it more difficult for you to do a Bohr diagram.
That’s why we are going to stop with argon having 18. Argon has 8 electrons in its outer energy. That
means that its outer energy level is full and argon is a happy element. It is not very reactive. It doesn’t
need anything to be happy because its outer energy level is already full. If we were to do the dot
diagram for argon it has 8 outer electrons so we would do the dot diagram like this. Remember that
atoms make up matter they are the smallest particle of matter. And atoms have protons which have a
positive charge, neutrons which are neutral have no charge, and electrons which have a negative
charge.