Molecular Compounds

Review

Ionic compounds contain positive ions and negative ions.Positive ions are usually metal ions.

• Except for NH4+1.

Negative ions are usually nonmetals or polyatomic ions.

An ionic bond is the force that holds oppositely charged ions together.

Covalent Bonds

Molecular compound – held together by covalent bonds

Covalent bond – happens when atoms share electrons to reach octet.Non-metal + non-metalMetalloid + non-metal

Covalent Bonds

H H

H H

Electrons now belong to both atoms. Both H atoms have 2 valence electrons (same as He)

Covalent Bonds

H

H

O

HHO

All atoms now have the same amount of electrons as a noble

gas (complete octets)

Covalent Bonds

Every covalent bond involves 2 e-

Sometimes atoms can form multiple bonds.

• Share more than 1 pair of e-.

OO C

OO C

N N

N NDouble bonds Triple bond

Salts vs. Molecules

Molecules exist as separate bundles of atoms.The forces between molecules are

much weaker than the forces within molecules.

Molecular compounds tend to melt and boil at much lower temperatures than ionic compounds.

Salts vs. Molecules

+ - + - + -

+ - + - +-

+ - + - + -

+ - + - +-

+ - + - + -

+ - + - +-

Very strong forces between ions.Very strong forces between atoms.

Weak forces between molecules.

Salts vs. Molecules

Compound Melting Point Boiling Point

NaCl 801º C 1413º C

KBr 734º C 1435º C

FeCl3 306º C decomposes at 315º C

H2O 0º C 100º C

SO2 -75.5º C -10º C

PCl3 -93.6º C 76.1º C

Ioni

c C

ompo

unds

(s

alts

)C

oval

ent C

ompo

unds

(m

olec

ules

)