Chemical Formula Writing & Nomenclature

Binary Molecules

Literally, binary molecules are combinations of two non-metal elements. We are going to limit the scope of this category however to non-hydrocarbon molecules (CxHy). And, since we’ve already covered acids, the binary acids (which are also binary molecules) will not be covered here either.

So what’s left?

Combinations of the elements:

F, Cl, Br, I, O, S, Se, N, P, C, and H

As a representative example, we’ll explore the combination of nitrogen and oxygen.

Since nitrogen is less electronegative, it goes first in the formula.

Now, we must consider all of those oxidation states that we have been ignoring so far.

N±3,5,4,2 O -2,-1 All of the oxidation states of the nitrogen can now be possible since it is covalently bonding. The oxygen however can still only be -2.

The –1 oxidation state of the oxygen only occurs in peroxides. Peroxides have two oxygen atoms singly bonded to each other functioning as 2 a -2 ion. O2

Here are our possible combinations:

N+3 + O-2 

N+5 + O-2 

N+4 + O-2 

N+2 + O-2 

Naming Binary Molecular Compounds

ide

1st element name root of 2nd element name

Prefix Prefix The prefix used =

di mono subscript on the tri di element. tetra tri

penta tetra hexa penta Note that “mono”

hepta hexa is never used on

octa hepta the first element nona octa in the formula. deca nona deca

Naming Examples:

CO2 and CO are both possible combination of ±4,2 carbon and oxygen since carbon is C .

CO2 is named: carbon dioxide

CO is named: carbon monoxide

Naming Practice:

SO2  sulfur dioxide

P2O5  diphosphorus pentoxide

PCl3  phosphorus trichloride

CCl4  carbon tetrachloride

PBr5  phosphorus pentabromide

Formula Writing Practice: dinitrogen pentoxide  N2O5 sulfur trioxide  SO3 carbon tetraiodide  CI4 carbon disulfide  CS2 dihydrogen monoxide  H2O

Mixed Practice

P2N3  diphosphorus trinitride

SF6  sulfur hexafluoride

phosphorous tribromide  PBr3 dinitrogen tetroxide N2O4

SeI4  selenium tetraiodide

SO3  sulfur trioxide

SeP2  selenium diphosphide