1. Covalent BONDS
Chapter 4 Section 2

2. Covalent Bonds Covalent Bonds – electrons are shared between two atoms
Both atoms “claim” the other’s electron as their own
The number of covalent bonds an atom can form depends on the number of valence electrons it needs to complete its outer shell.

3. O Covalent Bonds Ex) Water (H2O) H H 2H2 + O2  2H2O
Oxygen has 6 v.e.  it can form 2 covalent bonds (octet rule)
Hydrogen has 1 v.e.  it will form 1 covalent bond (only needs 2)
A covalent bond forms between each hydrogen and the oxygen atom O
2H2 + O2  2H2O H
shows a shared pair of e- H

4. Hydrogen
Because hydrogen only has one valence electron and needs 1 more, it tends to form covalent bonds easily…
even with itself!

5. Double Bonds
Sometimes atoms share two pairs of electrons…

6. Triple Bonds
Sometimes they share three pairs…

7. POLAR MOLECULES
Some atoms will pull more strongly on shared electrons than other atoms
The electron moves closer to the stronger pull, causing a slight electrical charge

8. Polar Molecules
Non-Polar Molecule – atoms pull equally on the shared electrons
Polar Molecule – covalent bond in which electrons are shared unequally creating a partial charge on either end

9. Naming Covalent Molecules
prefix  1st element  prefix  2nd element
Note: if 1st element only has one atom, no prefix is used
Prefixes are based on the number of atoms present:
Examples:
1 = mono
CO2
2 = di
H2O
3 = tri
CF4
4 = tetra
carbon dioxide
dihydrogen monoxide
carbon tetrafluoride

10. Properties of Covalent Molecules
Low Melting Point
Covalent molecules tend to melt at lower temperatures
Poor Conductors
Most covalent molecules are poor conductors of electricity (electrons do not flow easily)

11. Ionic vs. Covalent Type of Bond Electrons are… Forms Between…
Held Together by…
Ionic
Given or Taken
Metals and Non-Metals
Opposing charges
Covalent
Shared
Non-Metals
Shared Electron Pairs