Recaps.

Molecules and Covalent Bonds
-Molecules and compounds
1)When 2 or more atoms are chemically bonded together;a molecule is formed.
2)A molecule is a group of atoms chemically bonded together.
3)Most non-metallic elements are found in the molecular form.
4)If a molecule is made up of atoms of 2 or more different elements,a compound is formed.
5)A compound is a substance made when 2 or more elements are joined together by a chemical reaction.

COVALENT BONDING
1)Covalent bonds are usually formed between atoms of non-metals.
2)A sharing of electrons allow both to achieve a stable noble gas configuration.
3)If 2 atoms share
a)one pair of electrons=>a single bond is formed.
b)two pairs of electrons=>a double bond is formed.
c)three pairs of electrons=>a triple bond is formed.

4)Each atom contributes an equal number of electrons for sharing.

PROPERTIES OF COVALENT COMPOUNDS
1)Covalent compounds have low melting and boiling points
The molecules are held together by very weak van der waals force of attraction.Vey little energy is required to overcome these weak intermolecular forces.

2)Covalent compounds do not conduct electricity.
Molecules in covalent compounds do not carry charges.

3)Covalent compounds can dissolve in organic solvents but not in water.
Covalent molecules are not readily hydrated by water molecules.