The Naming of Chemical Compounds

Science > Chemistry > Introduction to Chemistry > Naming of Chemical Compounds

In this article, we shall study the method of naming of chemical compounds

In a chemical reaction, the molecular composition changes and it is represented by a chemical equation. In a chemical equation, the various substances involved as reactants or products are written in the form of symbols and formulae. These symbols and formulae are shorthand notations of the molecules involved as reactants or products.

Symbol of an Element:

A symbol is a representation of an atom of an element. These are unique 1,2, and 3 letter symbols. The first letter of an Element symbol is always a capital letter and remaining letters are written in lower case only. Many of the element symbols reflect the English name of the element such as Oxygen (O), hydrogen (H), carbon (C), nitrogen.(N), etc. These are single letter symbols. Examples of double letter symbols are aluminium (Al), Magnesium (Mg), calcium (Ca), etc.. Some symbols are derived from Latin names Aurum (gold) (Au), Argentum (silver), Stannum (tin) (Sn), Plumbum (lead) (Pb), etc.(Ag),

The formula of Element or Compound:

The formula is a representation of the actual number of atom or atoms of each element present in one molecule of the substance. The formula of element or compound is written by making use of the symbols of the respective elements. The formula for nitrogen is N₂, that of oxygen is O₂, that of carbon dioxide is CO₂, etc.

Radicals or Ions:

A radical is a group of atoms of elements carrying a charge, e.g., chlorate [ClO₃^–].

Radicals or ions are formed by losing or gaining electrons. When an electron is gained the group of atoms acquire a negative charge and is called a negative radical or negative ion.  When an electron is lost the group of atoms acquire a positive charge and is called a positive radical or positive ion. Depending upon the number of charges carried by radicals they are further classified as monovalent, bivalent (divalent), trivalent and tetravalent radicals or ions and so on.

Positive Radicals:

Valency	Radical	Symbol	Ion
Monovalent	Hydrogen	H	H +
Sodium	Na	Na +
Potassium	K	K +
Mercurous or Mercury (I)	Hg	Hg +
Cuprous or Copper (I)	Cu	Cu +
Argenous or silver (I)	Ag	Ag +
Divalent [2]	Zinc	Zn	Zn2+
Magnesium	Mg	Mg2+
Calcium	Ca	Ca2+
Cupric or Copper (II)	Cu	Cu2+
Mercuric or Mercury (II)	Hg	Hg2+
Frrrous or Iron (II)	Fe	Fe2+
Barium	Ba	Ba2+
Stanous or Tin (II)	Sn	Sn2+
Plumbous or Lead (II)	Pb	Pb2+
Trivalent [3]	Aluminium	Al	Al3+
Ferric or Iron (III)	Fe	Fe3+
Tetravalent [4]	Stanic or Tin (IV)	Sn	Sn4+
Plumbic or Lead (IV)	Pb	Pb4+

Note:

In the case of the electropositive element showing variable valency. For lower valency, its name is written in form ending with ‘ous’ while with higher valency its name is written ending with ‘ic’. For example, iron shows two valencies 2 and 3. the iron showing lower valency 2 is named as ferrous and by the IUPAC system, it is named Iron (II).  the iron showing higher valency r is named as ferric and by the IUPAC system, it is named Iron (III).

Negative Radicals:

Valency	Radical	Symbol	Ion
Monovalent	Hydroxyl or hydroxide	OH	OH –
Fluoride	F	F –
Chloride	Cl	Cl –
Bromide	Br	Br –
Iodide	I	I –
Nitrite	NO2	NO2 –
Nitrate	NO3	NO3–
Hypochlorite	ClO	ClO –
Chlorite	ClO2	ClO2 –
Chlorate	ClO3	ClO3 –
Perchlorate	ClO4	ClO4 –
Hypobromite	BrO	BrO –
Bromite	BrO2	BrO2 –
Bromate	BrO3	BrO3 –
Perbromate	BrO4	BrO4 –
Hypoiodite	IO	IO –
Iodite	IO2	IO2 –
Iodate	IO3	IO3–
Periodate	IO4	IO4 –
Acetate	CH3COO	CH3COO –
Formate	HCOO	HCOO –
Bisulphide	HS	HS –
Bisulphite [Hydrogen sulphite]	HSO3	HSO3 –
Bisulphate [Hydrogen sulphate]	HSO4	HSO4 –
Bicarbonate [Hydrogen carbonate]	HCO3	HCO3 –
Cyanide	CN	CN –
Cyanate	CNO	CNO –
Thiocyanate	SCN	SCN –
Permanganate	MnO4	MnO4–
Oxide	O	O2–
Divalent [2]
Peroxide	O2	O22-
Carbonate	CO3	CO32-
Sulphide	S	S2-
Sulphite	SO3	SO32-
Sulphate	SO4	SO42-
Thiosulphate	S2O3	S2O32-
Biphosphate [Hydrogen phosphate]	HPO4	HPO42-
Chromate	CrO4	CrO42-
Dichromate	Cr2O7	Cr2O72-
Oxalate	C2O4	C2O42-
Trivalent [3]	Phosphite	PO3	PO33-
Phosphate	PO4	PO43-

Derivation of Formulae of Compound:

Steps Involved:

• First, write electropositive element (say A) in its radical form ( Ax+) followed by the electronegative element (say B)  in its radical form ( Ay-). (Use tables for radicals).
• Below the element write their numeric charge without considering nature. ( x and y)
• Swap the numbers obtained in step 2 i.e. (y and x)
• Now the molecule should be electrically neutral. Hence the formula of the molecule is  AyBx

Formula for ferric chloride:

The formula for ferric chloride is FeCl₃.

Formula for ferric oxide:

The formula for ferric oxide is Fe₂.O₃.

Formula for Aluminium hydroxide:

The formula for Aluminium hydroxide is Al(OH)₃.

Formula for magnesium phosphite:

The formula for magnesium phosphate is Mg₃(PO₃)₂.

Naming Binary Compounds:

General Prefixes Used in Naming:

Number	Multiplier
1	mono-
2	di-
3	tri-
4	tetra-
5	penta-
6	hexa-
7	hepta-
8	octa-
9	nona-
10	deca-

Steps Involved in Naming:

• Write the molecular formula. Identify radicals.
• Find the valencies of constituent groups. It is important for elements showing variable valency.
• Name of electropositive or less electronegative element/ group is written first. (due consideration to be given to elements showing variable valency). followed by name of the electronegative or more electronegative element or group.

Compound	Name
NaCl	Sodium chloride
MgCl2	Magnesium chloride
CaCl2	Calcium chloride
BaO	Barium oxide
H2S	Hydrogen sulphide
FeCl3	Ferric chloride or Iron (II) chloride
FeCl2	Ferrous chloride  or Iron (III) chloride
SnCl2	Stannous chloride  or Tin (II) chloride
SnCl4	Stannic chloride  or Tin (IV) chloride
CuCl	Cuprous chloride or  Copper (I) chloride
CuCl2	Cupric Chloride  or  Copper (II) chloride
CO	Carbon monoxide
CO2	Carbon dioxide
SO2	Sulphur dioxide
SO3	Sulphur trioxide
CCl4	Carbon tetrachloride
P2O5	Phosphorous pentaoxide
UF6	Uranium hexafluoride

Naming of Acids:

Binary Acids:

They have general formula HA. The negative radical consists of a single non-metal. Use hydro as prefix and ic suffix.

Binary Acid	Name
HF	Hydrofluoric acid
HCl	Hydrochloric acid
HBr	Hydrobromic acid
HI	Hydroiodic acid

Binary Acid  Name:

Oxyacids:

The negative radical consists of non-metal and oxygen. If the percentage of oxygen is less, then suffix ous is used. If the percentage of oxygen is more, then the suffix ic is used.

Oxyacid	Name
H2SO3	Sulphurous acid
H2SO4	Sulphuric acid
HNO2	Nitrous acid
HNO3	Nitric acid
H3PO3	Phosphorous acid
H3PO4	Phosphoric acid

If acid contains less number of oxygen than its corresponding ‘ous’ acid a prefix hypo is given to the negative radical. If acid contains more number of oxygen than its corresponding ‘ic’ acid a prefix per is given to the negative

Acid	Name
HClO	Hypochlorous acid
HClO2	Chlorous acid
HClO3	Chloric acid
HClO4	Perchloric acid

Naming of Bases:

Base have general formula BOH. They contain hydroxyl (OH-) group. Metal is the electropositive radical and hydroxyl group is negative radical. The name of metal or group is written first followed by the word hydroxide.

Base	Name
NaOH	Sodium hydroxide
KOH	Potassium hydroxide
Al(OH)3	Aluminium hydroxide
Mg(OH)2	Magnesium hydroxide
NH4OH	Ammonium hydroxide

Naming of Salts:

Salt is assumed to be a product of neutralization reaction between acid and base. The positive radical of salt comes from the base while the negative radical comes from the acid. The name of salt is written with positive radical followed by negative radical.

In case of oxyacids, if the negative radical is derived from ic acid the suffix ate is used for naming the salt. if the negative radical is derived from ous acid the suffix ite is used for naming the salt.

Salts involving Binary acids:

Salt	Name
NaCl	Sodium chloride
NH4Cl	Ammonium chloride
CH3COONa	Sodium acetate
MgCl2	Magnesium chloride
KBr	Potassium bromide
KI	Potassium iodide

Salts involving oxyacids:

Salt	Corresponding  Acid	Suffix	Name
ZnSO4	Sulphuric acid ( H2SO4)	ate	Zinc sulphate
NaNO3	Nitric acid (HNO3)	ate	Sodium nitrate
AlPO4	Phosphoric acid (H3PO4)	ate	Aluminium phosphate
CaSO3	Sulphurous acid ( H2SO3)	ite	Calcium sulphite
ZnNO2	Nitrous acid ( HNO2)	ite	Zinc nitrite
Mg(PO)2	Magnesium phosphate	ite	Magnesium phosphite

In next article, we shall study next chapter: Laws of chemical combinations. In which we shall study dalton’s atomic theory, the law of conservation of mass, the law of definite proportion, the law of multiple proportions, the law of reciprocal proportions, Gay-Lussac’s law of combining volume.

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Science > Chemistry > Introduction to Chemistry > Naming of Chemical Compounds