1. Covalent Bonding

2. Covalent Bonds
Covalent bonds occur when two atoms share a pair of electrons.

3. Why does it work?
Atoms are most stable when the outer electron shell is full – octet rule
Some atoms can steal electrons from other atoms – ionic bonds
Metal + nonmetal

4. Why does it work?
Most nonmetals can not steal electrons from other nonmetals.
Share the electron instead – covalent bonds

5. How can we predict which bonds are covalent or ionic?
The difference in electronegativity of elements predicts ionic or covalent bonds.
If there is 1.8 or higher difference in electronegativity, the bond will be ionic.
Below 1.8 is covalent.

6. Determining the number of bonds an atom can form
The number of valance electrons determines the number of covalent bonds an atom can form.
Any valance electron that does not have a pair is free to bond.

7. Rules of Thumb for Covalent Bonds
Zero or eight valance electrons:
No bonds can be formed.
Four or less valance electrons:
Can form the same number of bonds as valance electrons because all of the electrons are free.

8. Rules of Thumb for Covalent Bonds
Five to seven valance electrons
The atom can only make bonds with the valance electrons that are not already paired.

9. Practice Problem 1
How many covalent bonds can calcium form?

10. Practice Problem 2
How many covalent bonds can arsenic form?