Chemical Formulas

 

Formulas show the makeup of a compound: how many atoms of each type are bonded together. When atoms bond together, regardless of whether they are those of elements or compounds, we call them molecules

 

·        For water:

 

 

 


H2O =

 

 

Notice that the number applies to the symbol to the left of the number. We have drawn one molecule of water.

 

·        For carbon dioxide

Oval: C
 


Oval: OOval: OCO2 =

 

 

 

 

 

Notice that the "2" does not apply to the carbon.

 

More examples:

 

Formula

Number of Atoms in each Molecule

BeCO3

Be: 1

C: 1

O: 3

Al(NO3)3

Al : 1

N: 1 X 3 = 3

O: 3 X 3 = 9

(NH4)2S

N: 2

H: 4 X 2 = 8

S: 1

 

 

 

Also notice that for in a single molecule of ammonium sulfide, [(NH4)2S], there are 11 atoms in all, of three different types.