Slide 1
Let’s learn about the atomic structure.
Slide 2
Each element is chemically unique. To understand why they are unique, you need to know the structure
of the atom and the characteristics of its components. The atom is the smallest particle of an element.
Slide 3
There are three subatomic particles in an atom – electrons, protons, and neutrons. Electrons have a
negative charge, no charge and they are located outside of the nucleus. Protons have a positive charge.
They have a mass of one atomic mass unit or 1 amu and they are found inside the nucleus. Neutrons
have no charge, an atomic mass of 1 atomic mass unit, and they are located inside the nucleus.
Slide 4
Atoms have 2 regions – the nucleus and the electron cloud. In the nucleus you have the protons and
neutrons. Overall, the nucleus has a positive charge and almost all of the mass is found within the
nucleus. Electron clouds include the electrons. This is the most volume of the atom meaning it takes up
the most space.
Slide 5
If we were to take a look at the periodic table, you would notice a number above each of the chemical
symbols. This represents the atomic number. The atomic number is the number of protons. The
number of protons what kind of atom it is. The atomic number is also the number of electrons found
within a neutral atom. So find Fluorine on your reference sheet. Identify the atomic number of
Fluorine on your reference sheet. The atomic number is 9. How many protons does Fluorine have? It
has 9 protons. How many electrons does it have? It has 9 electrons. The atomic number tells you how
many protons and the number of electrons.
Slide 6
Below the chemical symbol you’ll notice another number. This is the atomic mass number. The mass
number is the number of protons and neutrons. So, let’s do some math. The mass number is the
number of protons plus the number of neutrons. So find Fluorine on your reference table. Identify the
atomic mass of Fluorine. How many neutrons does Fluorine have? To find out how many neutrons
Fluorine has, you need to take the atomic mass minus the atomic number. So, 19 minus 9 and you get
10. So Fluorine has 10 neutrons.
Slide 7
Let’s do some more practice. Find carbon on your reference sheet. What is the atomic number of
carbon? What is the mass number? How many protons does carbon have? How many neutrons? How
many electrons?
Slide 8
The atomic number of carbon is 6. The atomic number again tells me that I have six protons and six
electrons for carbon. The mass number is 12.01. And remember the mass number tells the number of
protons plus neutrons. Round the mass number to the nearest whole number which would be twelve.
To find out how many neutrons, take the mass number minus the atomic number, so 12-6 and you get
6. Carbon has 6 neutrons.
Slide 9
Notice that the atomic mass number is just the atomic mass rounded off. Atomic mass is the mass which
we call the amu of a single atom. Mass number is the atomic mass rounded off and equals the number
of protons and neutrons together.
Slide 10
Let’s take a look at what isotopes are. Isotopes are atoms of the same element that have different
numbers of neutrons. Different numbers of neutrons mean different masses and different mass
numbers. So this is an isotope of Boron. They have the same number of protons and same number of
electrons, but they differ in the number of the neutrons. Boron 10 has 5 neutrons and Boron 11 has 6
neutrons making Boron 10 and Boron 11 isotopes. They are the same atom of the same element but
they differ in the number of neutrons.
Slide 11
Isotopes are like identical twins. They are almost exactly alike but not quite. For example, below are two
forms of carbon. Carbon 12 and Carbon 13. They are atoms of the same element but they differ in the
number of neutrons. Carbon 13 is heavier by one neutron than carbon 12.
Slide 12
Here is another example of an isotope. Lithium 6 and Lithium 7. They are atoms of the same element.
They have the same number of protons and electrons but they differ in the number of neutrons. Lithium
6 has three neutrons and Lithium 7 has 4 neutrons.
Slide 13
Find Chlorine on your reference sheet. Determine the following: the atomic number, the mass number,
the number of protons, the number of electrons, and the number of neutrons. The atomic number of
chlorine is 17. The mass number is 35. The atomic number again tells me that I have 17 protons and 17
electrons for chlorine. To find the number of neutrons I take 35-17 and I get 18 neutrons for chlorine.
Slide 14
Chlorine has an isotope, Chlorine-37. For Chlorine-37 the atomic number is 17 but the mass number is
37. The number of protons is 17. The number of electrons is 17. The number of neutrons is 37-17 which
means Chlorine-37 has 20 neutrons. Remember that isotopes have different number of neutrons and
because the mass number equals the number of neutrons plus the number of protons the mass number
will be different. Take a look at how Chlorine-37 can be written. It can be written as Chlorine-37, Cl-37,
or you can put the chemical symbol with 37 at the top representing your atomic mass and 17 on the
bottom representing the atomic number.
Slide 15
Bohr-Rutherford diagrams are used to show what the atom looks like. To draw them, you must show
the number of protons, neutrons, and electrons. Draw protons as the number of protons with a positive
charge. Neutrons with a little zero in the circle which we call the nucleus. You are going to be drawing
electrons in the shells around the nucleus. The filling order for electrons. 2 electrons can go in the first
energy level, 8 can go in the second energy level and 8 can go in the third energy level. Once we go past
the third energy level things get a little bit tricky.
Slide 16
Let’s draw the B-R diagram for helium. Find helium on your reference sheet. Figure of the number of
protons, number of electrons, and number of neutrons .
Slide 17
The number of protons equals 2. This is found by looking at the atomic number. The number of
electrons equals 2. Again you can find this by looking at the atomic number. The number of neutrons is
4-2. This is found by taking the mass number rounded minus the atomic number.
Slide 18
Now that we know that helium has 2 protons, 2 electrons, and 2 neutrons, draw a circle to represent the
nucleus. Remember protons and neutrons are found in the nucleus so put 2 protons with a positive
charge and 2 neutrons with no charge in the nucleus.
Slide 19
Next, draw your electrons in shells outside the nucleus. A shell is represented by a circle surrounding
the nucleus. Fill the shells with electrons. 2 electrons can fit in the 1st shell, 8 in the 2nd, 8 in the 3rd. And
again after the 3rd energy level things get a little bit tricky, so you are only responsible up to the third
energy level.
Slide 20
Helium has 2 electrons. Since the 1st shell can hold 2 electrons, put two dots representing electrons
anywhere on the shell.
Slide 21
Let’s do some practice. Draw the B-R diagram for Lithium. First, find Lithium on your reference sheet.
Determine the number of protons, neutrons, and electrons. Make a nucleus. Add your protons and
your neutrons. Next, make your electron shells. Fill in your electron shells according to the rule 2, 8,
and 8.
Slide 22
Here is what the B-R diagram for Lithium should look like. You have three protons, 4 neutrons in the
nucleus. In the first energy level you have 2 electrons and in the second energy level you have 1
electron.
Slide 23
Ions are created when an atom gains or loses one or more electrons. It acquires a net electrical charge.
The charge of the ion equals the number of protons – the number of electrons.
Slide 24
Remember atoms differ by the number of protons. Ions differ by the number of electrons. And isotopes
differ by the number of neutrons.