Naming and writing Formula of compounds:

Chemical compound has two parts =   + and – sides          A+B

A Compound is made of two or more different elements.

Positive side is original name of element as appears on periodic table. Positive side usually named first before negative side

Negative side is original name on periodic table but modified at the endings e.g. ine or gen becomes [ide] 

NaCl = Is made up of sodium and chlorine therefore name = Sodium Chloride

MgO = Magnesium and Oxygen = Magnesium Oxide

Elements in compounds have charges or valency or OXIDATION states = Group Number on Periodic table.

Charge of group: 1,2,3,4,5,6,7,8 is fixed. Don’t show charge in name.

Transition elements: Have variable charges therefore show charge number as Roman numeral in brackets between positive and negative.



2 main elements in compound.

Binary compounds of main group elements [1 …8].

Positive side first, negative side [ide]

HCl, HF, NaCl, MgO, AlN, Na2O, Mg3N2,  Al2O3 ,

Hydrogen Chloride

Sodium Chloride

Magnesium oxide

Aluminum nitride

Sodium oxide

Magnesium nitride

Aluminum oxide

Binary compounds of transition elements.

Write name of positive side first

Write the charge of transition element in Roman numeral in brackets after name of transition element.

Write negative side [ide] last.

Use the charge of the negative side (fixed) to find the charge of the positive side e.g. HgO , Hg2O ,  CuN3 , CuO , Cu2O , FeCl2 , FeCl3

Total charge on HgO = 0, Charge of Oxygen fixed = -2, therefore charge of Hg =+2 Roman numeral II,  Name of compound=Mercury(II)oxide

Total charge on Hg2O = 0, Charge of Oxygen fixed = -2 therefore charge of Hg =+1, Roman numeral I, Name of compound=Mercury(I)oxide

Name the rest of  the compounds


Have polyatomic ions

[ SO32-  = Sulfite] ,  [SO42-= Sulfate] ,  [CO32-=Carbonate] ,

[CN-=cyanide] , [PO4-3=Phosphate]  , [NO3=Nitrate],     [NO2=Nitrite]                  [NH4+= Ammonium] , [ClO3=Chlorate]


Naming or formula writing is similar to binary compound

Total charge = 0

Sodium Chlorate = NaClO3

Ammonium Chloride = NH4Cl

Use brackets if more than one ion is present

e.g.Calcium nitrate = Ca(NO3)2

CuClO3  ,  Cu(ClO3)2  ,  FeSO4 , Fe2(SO4)3

Charge on CuClO3 compound = 0 , Charge on chlorate ion ClO3 =-1 [Fixed] charge on Cu = +1 Roman numeral [I] name of compound = Copper(I)chlorate

Charge on  Cu(ClO3)compound = 0 ,Charge on chlorate ion ClO3 =-1 [Fixed] charge on Cu = 0 –[-1×2]=+2 Roman numeral [II] name of compound. Name of compound = Copper(II)chlorate

Name the remaining compounds.

Non-metal compounds

Name positive side with name on periodic table

Negative side end to ide.

Use prefixes e.g. di=2, tri=3, tetra=4 , penta=5 ,hexa=6  for number of elements more than one

Mono = one [can ignore mono sometimes]

N2O,    NO,     N2O4,     CO2 ,      CO ,     H2O ,    CCl4,   PCl5

Dinitrogen monoxide

Nitrogen monoxide

Dinitrogen tetraoxide

Name the rest.


Have hydrogen as positive ion. E.g. HCl , HCN

  1. Write name of positive side Hydro and then negative side ending ide changes and becomes ic acid. E.g. Hydrochloric acid , hydrocyanic acid

If Acid contains polyatomic ion with ate ending, ignore hydro and then change ending ate to ic acid. e.g. H2SO4, H3PO4

Sulfuric acid , Phosphoric acid

If Acid has name of polyatomic ion with ite ending . Change ite changes to ous acid  . e.g. H2SO3 , HNO2

Sufurous acid , Nitrous acid .

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