Radicals and Chemical Formulae

Radicals Ions How to write a chemical

formula

INDEX

 Radicals are atomic or molecular

species with unpaired electrons which are capable of independent

existence.

Radicals

Types of Radicals

Acid radicals:-The acid radical is an anion left after removal of hydrogen atoms from an acid.

Basic radicals:-The basic radical is the cation left after removal of OH or other alkaline group from the bases.

IONSAn ion is a charged species in which an atom or a group of atoms possess a net electric charge. The net electric charge of an ion can either be positive or negative. Positively charged ions are called cations and negatively charged ions are called anions.

Cations are atoms that have lost an electron to become positively charged.

The ions of all the metal elements are cations.

If an atom loses one electron, then the cation formed has 1 unit positive charge.

Examples:- Na+ , Zn2+, Mg2+, Al3+ etc.

CATION

Anions are atoms or groups of atoms that have gained electrons. Having more negatively charged electrons than positively charged protons, they are negatively charged. 

Most anions are composed from multiple atoms, and are called polyatomic ions.

Examples:- Cl− , O2- , co32-, PO4

3- etc.

 

ANIONS

Chemical formula of a compound is the symbolic representation of its atomic constituents. In other words, a chemical formula represents the composition of a molecule in terms of the symbols of the elements present in that molecule. To write the chemical formula of a compound, one should have prior knowledge of two things.

1.The symbols of the constituent elements, and2.The combining capacity of each atom constituting the compound

Chemical Formula

VALENCY

The combining power or the combining capacity of an atom or an element is called its valency. The number of atoms of other elements with which one atom of an element combines is decided by the valency of that element.

For example, both hydrogen and chlorine have a valency of 1. Therefore, one atom of hydrogen reacts with one atom of chlorine to form one molecule of hydrogen chloride.

The valency of an ion is equal to the charge on it.

The valencies of some common ions are given in the following table.

Name of ion

Symbol Valency Name of ion

Symbol Valency

Aluminium Al3+ 3 Sulphite SO32- 2

Ammonium

NH4+ 1 Bromide Br− 1

Calcium Ca2+ 2 Carbonate CO32- 2

Copper(II) Cu2+ 2 Chloride Cl− 1

Hydrogen H+ 1 Hydride H− 1

Iron(III) Fe3+ 3 Hydroxide OH− 1

Potassium K+ 1 Oxide O2− 2

Zinc Zn2+ 2 Sulphide S2− 2

1.Write the symbols of the elements which form a compound.

STEPS TO WRITE A CHEMICAL FORMULA

If we have to write the formula of hydrogen sulphide. First write down the symbols of hydrogen and sulphur.

Symbols: H S

2. Below the symbol of each element, write down its valency.

Symbols: H S

Valencies: 1 2

3.Finally cross-over the valencies of the combining atoms. This will give the

required formula.

Symbols: H S

Valencies: 1 2

THE REQUIRED FORMULA ISH2S1 or H2S

Formula of some compounds

Chemical compounds Chemical Formula

Silver chloride AgCl

Aluminium nitrate Al(NO3)3

Barium chloride BaCl2

Calcium carbonate CaCO3

Potassium nitrate KNO3

Magnesium aluminate Mg(AlO2)2

Sodium carbonate Na2CO3

Made by-Rohit Garg