MOLECULAR COMPOUNDS

What are they and how to name them?

Definition: A compound formed when atoms of two or more different elements share electrons

• Usually formed between 2 or more non-metals and are also called covalent compounds

Molecular Compounds

Smaller compounds

with 2-3 atoms linked

Lattice structure (solids)

What do they form?

Non-metal to non-metal

Metal to non-metal

What bonds with what?

Atoms share electrons to complete

valence shells

Transfer of electron opposite charges attract

How atoms bond?

Molecular Compounds

Ionic Compounds

Ionic vs. Molecular?

Ionic Covalent

Naming Molecular Compounds

Naming molecular compounds is different from ionic and polyatomic compounds. In molecular compounds the name uses a prefix to indicate the number of each atom present.

Example: Carbon Dioxide tells us it is made of carbon and oxygen in a ratio of 1 carbon atoms to 2 oxygen atoms.

Prefixes

(P4O10) tetraphosphorous decaoxide

10deca9nona8octa7hepta

(SF6) sulfur hexafluoride6hexa(PBr5) phosphorus

pentabromide5penta

(CF4) carbon tetrafluoride4tetra(SO3) sulfur trioxide3tri(CO2) carbon dioxide2di

(CO) carbon monoxide1mono

ExampleNumber of atoms

Prefix

Writing Names1. Count the # of atoms of the first

element.2. Write the prefix for this number

followed by the name of the first element. If there is only one of the first element we leave out the prefix.

3. Count the # of atoms of the second element.

4. Write the prefix for this number followed by the name of the element using the suffix –ide.

ExamplesN2O4

Nitrogen atoms = 2 dinitrogenOxygen atoms = 4 tetraoxide

Full name = dinitrogen tetraoxide

C2F6

Carbon atoms = 2 dicarbonFluoride atoms = 6 hexafluorideFull name = dicarbon hexafluoride

Writing Formulas

1. Write the symbol for the elements.

2. Write the subscript for the number of atoms represented by the prefix.

3. Notice—the ratio in the formula is not reduced to its simplest form like ionic compounds.

sulfur trioxideSO3

diphosphorus pentasulfideP2S5

Examples

Diatomic ElementsSome elements are diatomic. This means

they exist naturally as two of the same element bonded together

Examples:Hydrogen gas H2 Bromine liquid Br2 Oxygen gas O2 Iodine solid

I2Nitrogen gas N2 Fluorine gas

F2

Chlorine gas Cl2