How to learn naming Chemical Formulae

How to learn naming Chemical Formulae?

1. A formula is a shorthand notation used to identify the composition of a molecule or compound.

2. For example chemical formula of water is H2O. It includes the symbol of each element (e.g. Hydrogen:H and Oxygen:O)  in the molecule, along with numerical subscripts to show how many atoms of each element are present.

3. Most of the inorganic compounds are binary compounds i.e. it consists of two elements. Some are ternary i.e. contain more than two elements.

4. Compounds may be ionic compounds i.e. elements have ionic bonds. Or these can be covalent bonded. Generally, metal element forms ionic bond with non-metal element. Compounds having non-metals only have covalent bonding.

5. An atom or group of atoms with either a positive or a negative charge is called an Ion

6. Cations are positively charged ions.

7. Anions are negatively charged ions (Are Negative IONS)

8. Monatomic Ion means a single atom ion (mono = one) Ex: Na+ or Cl-

9. Polyatomic Ion means a group of atom ions (poly means many) which acts together as single unit. For example: Nitrate polyatomic ion NO3- (1 Nitrogen atom, 3 Oxygen atoms has one extra electron and thus is negatively charged 1-).

10. For binary compounds containing  a metal and a non-metal, metal is always named first, followed by a name derived from the root name for the nonmetal. E.g. Common Salt NaCl consists metal (cation: Na+) and non-metal Chlorine becomes chloride here (anion: Cl-

11. Usually anions of an element carrying one negative charge (1-) have suffix -ide
 

Element Anion                  Name used in formula   
Cl- Chloride
F- Fluoride
Br- Bromide
I- Iodide
O2- Oxide
S2- Sulphide
H- Hydride
Au- Auride
N3- Nitride
P3- Phosphide
As3- Arsenide

 

12.  The net charge on an ionic compound is always zero. E.g. In NaCl, one cation(Na1+) and one anion(Cl1-), makes the net charge (1+ + 1- = 0) zero. Similarly, in AlCl3. one cation (Al3+ ) and three anions (Cl1-), makes the net charge(3+ + 3(1-)= 0) zero.

13. Anions carrying oxygen+another element are called -oxy anions. In general, for -oxy anions we use suffix -ate is used. Few examples are:

 

  -oxy Anion                  Name used in formula   
CO32- Carbonate
SO42- Sulphate
SiO32- Silicate
ZnO32- Zincate

 

14. In case of -oxy anions, if non-metal element exists with oxygen in more than one charged (or oxidation) state, then we use suffix -ite for the lower charged state and -atefor higher charged state.
 

-oxy Anion  Name used in formula
SO32- Sulphite
SO42- Sulphate
NO2- Nitrite
NO3- Nitrate
SnO22- Stannite
SnO32- Stannate


15. In case of -oxy anions, if more than two oxidation (charged) states exist, we use the following naming convention (Note: It is old traditional system, still in use. IUPAC time to time releases new nomenclature standards). 
 

Oxidation State  prefix- or -suffix 
used in Anions
Lowest Hypo- -ite
. -ite
. -ate
. per- -ate
Highest Hyper- -ate


An example of this:
 

-oxy Anion  Name used in formula
ClO- Hypochlorite
ClO2- Chlorite
ClO3- Chlorate
ClO4- Perchlorate
HPO32- Phosphite
H2PO2- Hypophosphite


16. When an polyatomic anion has H- associated with it, we use bi- or hydrogen- as suffix root name.
For example,
 

Polyatomic Anion
with H-
 Name used in formula
HCO3- bicarbonate 
or hydrogen carbonate
HSO4- bisulphate or
hydrogen sulphate
HSO3- bisulphite or
hydrogen sulphite
HS- bisulphide or 
hyderogen sulphide
HPO42- monohydrogen phosphate
H2PO4- dihydrogen phosphate

(Note: to represent number of atoms, prefixes like mon-, bi-, di-, tri- etc. are used).

17. List of a few other polyatomic anions
 

Polyatomic Anions Name used in formula
OH- Hydroxide
O2- Superoxide
O3- Ozonide
NH2- Amide 
N3- Azide
CN- Cyanide
OCN- Cyanate
SCN- thiocynate
CrO22- Chromate
Cr2O72- DiChromate
MnO42- Manganate
MnO4- Permangnate
CH3COO- Acetate
C2O42- Oxalate
PO43- Phosphate


18. List of Cations whose charge do not vary
 

Single Charge     Double Charge   Triple Charge
Hydrogen H+ Beryllium Be2+ Aluminium Al3+
Lithium Li+ Magnesium Mg2+
Sodium Na+ Calcium Ca2+
Potassium K+ Strontium Sr2+
Cesium Cs+ Barium Ba2+
Rubidium Rb+ Zinc Zn2+
Silver Ag+ Cadmium Cd2+
Ammonium NH4+



19. Following is the list of cations whose charges vary. In traditional system, we use suffix -ous with lower charged state and -ic withhigher charged state. The new IUPAC method, the charged state is represented with Roman numerals within parentheses.For example:
 

Element Cation  IUAPC Name Tradional Name Example
Copper Cu+ Copper(I) Cuprous
Copper Cu2+ Copper(II) Cupric
Gold Au+ Gold(I) Aurous AuCl Gold(I) Choloride
or Aurous Chloride
Gold Au3+ Gold(III) Auric AuCl3 Gold (III) Chloride 
or Auric Chloride
Iron Fe2+ Iron(II) Ferrous
Iron Fe3+ Iron(III) Ferric
Mercury Hg+ Mercury(I) Mercurous
Mercury Hg2+ Mercury(II) Mercuric
Chromium Cr2+ Chromium(II)
Chromium Cr3+ Chromium(III)
Chromium Cr6+ Chromium(VI)
Cobalt Co2+ Cobalt(II)
Cobalt Co3+ Cobalt(III)
Manganese Mn2+ Manganese(II)
Manganese Mn3+ Manganese(III)
Manganese Mn7+ Manganese(VII)



20. In some cases cations containing non-metals, we use suffix -nium
For example:
 

Cations Name used in formula
NH4+ Ammonium
NH2H5+ Hydrazinium
C5H6N+ pyridinium
H3O+ Hydronium 
NO2+ Nitronium


21. Acid is any substance that has one or more replaceable hydrogen ions (H+). 

22. Acids which do not contain oxygen are named with prefix hydro-

A few examples are:
 

Acid Name
HF Hydroflouro acid
HCl Hydrochloric acid
HBr Hydrobromic acid
HI Hydroiodic acid
HCN Hydrocyanic acid
H2S Hydrosulphuric acid or Hydrogen Sulphide
(Do not confuse with Sulphuric acid H2SO4)
HN3 Hydrazoic acid


23. List of acids which contain oxygen.
 

Acid Name
H2CO3 Carbonic acid
H3CO3 Boric acid
H4SiO4 Silicic acid
HNO3 Nitric acid
HNO2 Nitrous acid
H2SO4 Sulphuric acid
H2SO3 Sulphurous acid
H2S2O3 Thiosulphuric acid
H2CrO4 Chromic acid
H2Cr2O7 Dichromic acid
H3PO4 Phosphoric acid
H3PO3 Phosphorous acid
H3AsO4 Arsenic acid
H3AsO3 Arsenious acid
HClO4 Perchloric acid
HClO3 Chloric acid
HClO2 Chlorous acid
HClO Hypochlorous acid
HMnO4 Permanganic acid
HOCN Cyanic acid
HSCN Thiocyamc acid
CH3COOH  Acetic acid
H2C2O4 Oxalic acid

 

Q1: Write the chemical formula of the following. List the cations and anions present.

(a) sodium chloride

(b) potassium iodide

(c) calcium sulfide

(d) cesium bromide

(e) magnesium oxide

Answer:  

(a) sodium chloride:  NaCl (Na+, Cl-)

(b) potassium iodide: KI (K+, I-)

(c) calcium sulfide: CaS(Ca2+, S2-)

(d) cesium bromide: CsBr (Cs+, Br-)

(e) magnesium oxide: MgO (Mg2+, O2-)

Q2: Name the following binary compounds.

(a) AlCl3

(b) CsF 

(c) MgI2 

(d) CaCl2 

(e) LiCl

(f) MgS

(g) Rb2O

(h) CaO


Answer:  

(a) AlCl3: Aluminium Chloride

(b) CsF  : Cesium Fluoride

(c) MgI2: Magnesium Iodide

(d) CaCl2: Calcium Chloride

(e) LiCl : Lithium Chloride

(f) MgS : Magnesium Oxide

(g) Rb2O : Rubidium oxide

(h) CaO: Calcium Oxide


Q3: Give chemical formula for the following compounds.

(a) iron (III) Chloride 

(b) ferric oxide

(c) sodium hydroxide

(d) cobaltous hydroxide or cobalt(II) hydroxide

(e) tin (IV) Hydroxide

(f) mercuric cyanide 

Answer: 

(a) iron (III) Chloride:  FeCl3:

(b) ferric oxide: Fe2O3

(c) sodium hydroxide: NaOH

(d) cobaltous hydroxide or cobalt(II) hydroxide: Co(OH)2 

(e) tin (IV) hydroxide: Sn(OH)4 

(f) mercuric cyanide: Hg(CN)2

Q4: Give chemical formula for the following compounds:

  1. Potassium chlorite
  2. Magnesium sulphite
  3. Chromium sulphate
  4. Sodium acetate
  5. Lead chloride
  6. Cuprous iodide
  7. Copper(II) sulphide
  8. Ferric chlorite
  9. Mercuric chloride
  10. Barium peroxide
  11. Strontium silicate
  12. Cobalt (III) nitrate
  13. Lithium hydride
  14. Ammonium cyanate
  15. Strontium manganate
  16. Silver oxalate
  17. Calcium phosphide
  18. Radium phosphate
  19. Aluminium nitride
  20. Zinc nitrate

Answer(incomplete): 

  1. Potassium chlorite : KClO2
  2. Magnesium sulphite: MgSO3
  3. Chromium (III) sulphate: Cr2(SO4)3
  4. Sodium acetate: CH3COONa
  5. Lead chloride: PbCl2
  6. Cuprous iodide: CuI
  7. Copper(II) sulphide: CuS
  8. Ferric chlorite: Fe(ClO2)3
  9. Mercuric chloride: Mercury(II) Chloride - HgCl2
  10. Barium peroxide: BaO2
  11. Strontium silicate
  12. Cobalt (III) nitrate
  13. Lithium hydride
  14. Ammonium cyanate
  15. Strontium manganate
  16. Silver oxalate
  17. Calcium phosphide
  18. Radium phosphate
  19. Aluminium nitride
  20. Zinc nitrate

 

 

 

 

 

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