Valence electrons are the outermost shell electrons of an atom that are involved in bonding. Elements in the same group on the periodic table have the same number of valence electrons because they exhibit similar chemical properties based on their valence electron configuration. Atoms seek to attain a full outer shell of 8 electrons to achieve stability through gaining, losing or sharing valence electrons in chemical bonds.

1. Valence Electrons

2. What is a Valence Electron?
Valence electrons are the electrons in the outer shell
that bond with other atoms

3. What is a Valence Electron?
Valence electrons are the electrons in the outer shell
that bond with other atoms
= valence electron

4. What is a Valence Electron?
Valence electrons are the electrons in the outer shell
that bond with other atoms
= valence electron

5. What is a Valence Electron?
Valence electrons are the electrons in the outer shell
that bond with other atoms
Core electrons are under valence electrons
= valence electron

6. Outer Shells of Electrons
The number of valence electrons determines an
element’s chemical properties
For example, the noble gases on the right side of the
periodic table are inert
Inert = do not react with other atoms

7. Noble Gases
Noble gases are inert
because they have 8
outer shell (=valence)
electrons
Having 8 outer shell
electrons means the
outer shell is full, and
therefore can’t react

8. Periodic Table Groups
Columns on the periodic
table are called GROUPS
Elements in the same
group have similar
chemical properties.
This is because each group has the
same number of valence electrons

9. Valence Electrons in Groups
Elements in the periodic table are arranged in groups.
Each group has the same number of valence electrons….
Group 5A
Group 1A
Group 2A
Group 4A
Group 3A
Group 7A
Group 6A
Group 8A
Group 1A has 1
valence
electron, group
2A has 2
valence
electrons,
group 3A has 3
valence
electrons……….

10. Importance of Valence Electrons
The entire periodic table is arranged according to the
number of valence electrons each element has!!
The reason they arrange the periodic table this way is
because elements in each group react similarly (=same)

11. Octet Rule
The octet rule states that atoms like to have 8 valence
electrons.
Atoms that have 8 outer shell electrons are stable and
non reactive.
The noble gases
(group 8A) are
stable because
they all have 8
valence electrons

12. Lewis Structures
Lewis structures show ONLY valence electrons.
Examples:
Sodium (Na) is in group 1A,
so we know it has 1 valence
electron. Group 1A is
known as the alkali metals
Beryllium (Be) is in group
2A, so we know it has 2
valence electrons. Group
2A is known as the alkaline
earth metals

13. Lewis Structures
Lewis structures for oxygen
Oxygen is in group 6A, so it has 6 valence electrons.

14. How to Draw Lewis Structures
1) Look at the element you want to draw the structure for
and see what group it is in.
2) Draw dots around the symbol according to how many
valence electrons it has.
Example: Draw a Lewis Structure for calcium
1) We see calcium (Ca) is
in group 2A, so it has 2
valence electrons
2)
Ca

15. Filling Electron Orbitals
Electrons fly around atoms in
their electron orbitals
There are S, P, D and F orbitals
We will only study 1S, 2S, 2P,
3S and 3P orbitals.
Orbitals fill in this order
1S is first
2S is second, then 2P……

16. Filling Electron Orbitals
Electron orbitals will fill in this order:
1S___ 2S___ 2P___ ___ ___ 3S___ 3P___ ___ ___
“1” means first energy level
Valence electrons are ONLY in the highest energy level!!

17. Filling Electron Orbitals
Electron orbitals will fill in this order:
1S___ 2S___ 2P___ ___ ___ 3S___ 3P___ ___ ___
“1” means first energy level
Valence electrons are ONLY in the highest energy level!!
“S” is the type, or shape of the orbital
1S orbital is round

18. Filling Electron Orbitals
Electron orbitals will fill in this order:
1S___ 2S___ 2P___ ___ ___ 3S___ 3P___ ___ ___
“2” is the second energy level
Valence electrons are ONLY in the highest energy level!!

19. Filling Electron Orbitals
Electron orbitals will fill in this order:
1S___ 2S___ 2P___ ___ ___ 3S___ 3P___ ___ ___
“2” is the second energy level
Valence electrons are ONLY in the highest energy level!!
“S” and “P” are the type, or shape of the orbitals
2S orbitals are round
2P orbitals

20. How to Fill Electron Orbitals
Example: give me the electron orbital configuration of sodium (Na)
1) We look at the periodic
table and see that sodium
has 11 electrons
2) Electrons are filled in the
following order
The 1S 2S and 2P electrons are CORE electrons; they don’t react
The 3S (highest energy level) will react; Na has ONE valence electron

21. Remember What We are Doing!!
Hydrogen (H) atom
We are showing what orbitals
electrons are in, and how many are
in them. What is the electron
orbital configuration of Hydrogen?
“n” is the energy level, and
corresponds to our electron
diagram
n=1
1S___ 2S___ 2P___ ___ ___ 3S___ 3P___ ___ ___
H: 1S___ 2S___ 2P___ ___ ___ 3S___ 3P___ ___ ___

22. Remember What We are Doing!!
Hydrogen (H) atom
We are showing what orbitals
electrons are in, and how many are
in them. What is the electron
orbital configuration of hydrogen?
“n” is the energy level, and
corresponds to our electron
diagram
n=1
1S___ 2S___ 2P___ ___ ___ 3S___ 3P___ ___ ___
H: 1S___ 2S___ 2P___ ___ ___ 3S___ 3P___ ___ ___

23. Remember What We are Doing!!
Hydrogen (H) atom
n=1
We are showing what orbitals
electrons are in, and how many are
in them. What is the electron
orbital configuration of carbon?
“n” is the energy level, and
corresponds to our electron
diagram
n=2
1S___ 2S___ 2P___ ___ ___ 3S___ 3P___ ___ ___
C: 1S___ 2S___ 2P___ ___ ___ 3S___ 3P___ ___ ___

24. Remember What We are Doing!!
Hydrogen (H) atom
n=1
We are showing what orbitals
electrons are in, and how many are
in them. What is the electron
orbital configuration of carbon?
“n” is the energy level, and
corresponds to our electron
diagram
n=2
1S___ 2S___ 2P___ ___ ___ 3S___ 3P___ ___ ___
C: 1S___ 2S___ 2P___ ___ ___ 3S___ 3P___ ___ ___

25. Remember What We are Doing!!
Hydrogen (H) atom
n=1
We are showing what orbitals
electrons are in, and how many are
in them. What is the electron
orbital configuration of carbon?
“n” is the energy level, and
corresponds to our electron
diagram
n=2
1S___ 2S___ 2P___ ___ ___ 3S___ 3P___ ___ ___
C: 1S___ 2S___ 2P___ ___ ___ 3S___ 3P___ ___ ___

26. Remember What We are Doing!!
Hydrogen (H) atom
n=1
We are showing what orbitals
electrons are in, and how many are
in them. What is the electron
orbital configuration of carbon?
“n” is the energy level, and
corresponds to our electron
diagram
n=2
1S___ 2S___ 2P___ ___ ___ 3S___ 3P___ ___ ___
C: 1S___ 2S___ 2P___ ___ ___ 3S___ 3P___ ___ ___

27. How to Fill Electron Orbitals
Example: give me the electron orbital configuration of neon (Ne)
1) We look at the periodic table and see that neon
(Ne) has 10 electrons (electrons = to # of protons)
2) Electrons are filled in the following order
Lower level core electrons (level 1 here) DON’T react!
Level 2 (highest energy level) will react; Ne has 8 valence electrons!

28. Examples
Remember, only the highest
level (number) are valence
electrons:
-Li only has 1 valence
electron (2nd level)
-Mg only has 2 valence
electrons (3rd level)
You can see why atoms like
Ne are “happy” (=stable)
with 8 electrons now; their
valence shell is full and they
don’t want to give or lose
electrons.

29. Questions 20 Points!!
1. What is a valence electron? Draw an atom and show the valence electrons.
2. How many valence electrons do the following elements have:
Si, C, O, Ar, K
3. What does inert mean?
4. How many valence electrons do atoms like to have?
5. What do “groups” on the periodic table have in common?
6. Draw the Lewis structure for the following elements:
Ne, P, Mg, Na, Pb, Sb
7. Fill out the electron orbitals for the following elements
He, Ne, Na, Cl, B, Ar
Use the below diagram to guide you:
1S___ 2S___ 2P___ ___ ___ 3S___ 3P___ ___ ___
Bonus question: what element has the following electron configuration?
1s22s22p63s23p64s23d104p65s1