1. Understanding Electrons

2. Quick Review
J.J. Thomson discovered the electron using a cathode ray tube. The fact that the ray was deflected by a magnet meant the beam was made of particles. The fact that it was attracted to the positive electric charge meant that these electrons were negatively charged (opposites attract).

3. Quick Review
The atoms of each element behave very differently, but they all have something very important in common.
Every atom is made of the same subatomic particles:
Protons
Neutrons
Electrons

4. Quick Review Atom Protons have a positive charge.
Neutrons have zero charge.
They are neutral and not positive or negative.
Electrons have a negative charge.
Atom

5. In order to understand chemistry, you have to understand the structure of atoms.
Electrons fly around freely in the Electron Cloud.
Protons and Neutrons are joined together in the nucleus.

6. Atoms have the same number of protons and .
electrons
We do not typically identify an element by its electrons because unlike protons, electrons are gained, lost and shared between atoms.

7. Chemical reactions occur because atoms gain, lose and share electrons!
This idea is the foundation of chemistry:
Chemical reactions occur because atoms gain, lose and share electrons!
Remember: Electrons are found travelling around the nucleus in the electron cloud!

8. Determine how many electrons are in an atom of each of the following elements.12 16 22 46 57 36 3 24

9. nucleus 1st Energy Level 2nd Energy Level 3rd Energy Level
Electrons are not flying around the nucleus without any order. They organize themselves into energy levels.
When we draw atoms, we always have the nucleus in the middle. Each energy level is shown with a circle. The black dots represent the electrons in that energy level.
nucleus
1st Energy Level
2nd Energy Level
3rd Energy Level

10. s holds up to 2 electrons p holds up to 6 electrons
Each energy level is broken down into sublevels. There are ___ sublevels that you need to be familiar with. The higher the energy level, the more sublevels it will have. 4
Sublevels:
s holds up to 2 electrons
p holds up to 6 electrons
d holds up to 10 electrons
f holds up to 14 electrons

11. Label the periodic table on your notes.
Part of the way the periodic table is arranged is based on which sublevels are in the outer energy level of each elements atoms.
Label the periodic table on your notes. p s d f

12. Each energy level has an additional sublevel from the energy level before.
nucleus
The 1st Energy Level only has an s sublevel.
s = 2 electrons
The 2nd Energy Level has an s and p sublevel.
The 3rd Energy Level has an s, p and d sublevel.
s + p = = 8 electrons
s + p + d = = 18 electrons

13. The f sublevel does not appear until the 6th energy level starts being filled!

14. Filling in a electrons:
Phosphorous
15 electrons
Step 1:
Step 3:
Use your periodic table to determine how many electrons are in an atom of this element.
If an atom has more than 2 electrons, place up to 8 more in the second energy level.
Step 4:
Step 2:
If an atom has more than 10 electrons, place up to 18 more in the third energy level.
Place up to 2 electrons in the first level.

15. Complete the Bohr model diagrams on your notes by placing the correct number of electrons in each energy level.

16. Remember, while atoms begin with the same number of electrons as protons, electrons can gain, lose or share electrons.
When you are predicting how electrons will be gained, lost or shared, the total number of electrons is less important than number of
valence electrons

17. Valence electrons are the electrons in the outer energy level.
How many valence electrons do each of the following atoms have?
1 valence electron
5 valence electrons
2 valence electrons

18. Decide how many valence electrons are in each of the atoms on your notes.8 4 1 7

19. This is what the numbers attached to the A’s and B’s are for!
Valence electrons can be predicted for an atom by using the periodic table.
This is what the numbers attached to the A’s and B’s are for!

20. All of the elements in group I have
Elements in the same column or group have similar physical and chemical properties because they all have the same number of
valence electrons!
All of the elements in group I have
1 valence electron

21. How many valence electrons do the elements of group 2 have?
5B = 5
You will ignore the A’s and B’s. We will learn what those mean soon.

22. How many valence electrons do the elements of group 17 have?

23. Use your periodic table to determine how many valence electrons are in each of the elements on your notes. 4 5 8 2 2 7

24. Which Lewis Dot Diagram below accurately represents hydrogen?
Lewis Dot Diagrams:
Lewis dot structures show the number of valence electrons in an atom using an atoms symbol surrounded by dots representing the valence electrons.
Which Lewis Dot Diagram below accurately represents hydrogen? H H H

25. Which Lewis Dot Diagram below accurately represents nitrogen?
Which Lewis Dot Diagram below accurately represents carbon? C C C

26. For each of the examples on your notes, circle the Lewis Dot Diagram that shows the correct number of valence electrons for each element.

27. This means that the s and p sublevels are both full.
The Octet Rule:
Atoms are most stable when they have __ valence electrons in their outer energy level. 8
This means that the s and p sublevels are both full.
s + p = = 8 valence electrons

28. Which group on the periodic table has 8 electrons in its outer energy level naturally?
The Noble Gases
Group 18 undergoes the fewest chemical reactions of any of the elements on the periodic table. They are inert gases. This is a chemical property that means they will not react with other substances.
Inert means inactive!

29. Remember: Group 18 (The Noble Gases) undergo the fewest reactions because they have 8 valence electrons.
Neon
Argon

30. So why is Helium a noble gas?1 2
Since Helium only has 1 energy level, it only needs 2 electrons to have a full energy level.
It will not gain, lose, or share electrons because its energy level is full. This makes it an inert noble gas.