1. Valence Electrons
Cornell Notes

2. Valence Electrons
2-8-8 Rule
Electrons orbit the nucleus in energy levels within the electron cloud
The 1st energy level holds 2 electrons
The 2nd and 3rd energy levels holds 8 electrons 1 2 1 2 1 8 8 3 3 7 7 4 4 2 6 5 6 5

3. Valence Electrons
Valence Electron
Valence electrons: electrons in the last shell or energy level of an atom. 1 2
Last energy level: Level 3 1 2 1 8 3 3
So count the electrons in the last energy level 7 4 4 2 6 5
6 Valence Electrons! 6 5

4. How many valence electrons are in this atom?1 2 3 1 2 1 8 3 3
Valence Electrons 7 4 2 6 5

5. How many valence electrons are in this atom?5 1 2 1 3
Valence Electrons 4 2 5

6. How many valence electrons are in this atom?1 1
Valence Electrons

7. How many valence electrons are in this atom?2 1 2 1
Valence Electrons 2

8. Valence Electrons “Happy" atoms are stable atoms
Atoms are stable when their outermost energy levels (shells) are full 1 2 1 2 1 2 1 1 1 8 3 8 8 3 3 7 4 7 7 4 4 2 2 2
Stable 6 5 6 5
Stable 6 5
Stable

9. Valence Electrons
Is this atom stable? 1 2 1 8 3 7 4 2 6 5
YES!

10. Valence Electrons NO! Is this atom stable? 1 2 1 2 1 8 3 3 7 7 4 4 2 65 6 5
NO!

11. Valence Electrons Sad atoms are not stable
When an atom's outermost shell is not complete/full it is not stable.

12. Valence Electrons
Is this atom unstable? 1 2 1 8 3 7 4 2 6 5
NO!

13. Valence Electrons YES! Is this atom unstable? 1 2 1 2 1 8 3 3 7 7 4 46 5 6 5
YES!

14. Valence Electrons
Sad Atoms
Atoms become stable by bonding (joining) with other elements.
Bonded atoms are called molecules.
A covalent bond is one where atoms share electrons.
An ionic bond is one where electrons are either given or taken, not shared.