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
 

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

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.
 

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). 
 

An example of this:
 

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

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

17. List of a few other polyatomic anions
 

18. List of Cations whose charge do not vary
 

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:
 

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

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:
 

23. List of acids which contain oxygen.
 

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⁺, S^2-)

(d) cesium bromide: CsBr (Cs⁺, Br^-)

(e) magnesium oxide: MgO (Mg²⁺, O^2-)

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