1. Radicals and Chemical
Formulae

2.  Radicals
 Ions
 How to write a chemical formula

3. Radicals are atomic or molecular species
with unpaired electrons which are capable
of independent existence.

4. 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.

5. An 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.

6. 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.

7. 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- , co3
2-, PO4
3- etc.
ANIONS

8. 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, and
2.The combining capacity of each atom constituting the
compound

9. 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.

10. Name of
ion
Symbol Valency Name of
ion
Symbol Valency
Aluminium Al3+ 3 Sulphite SO3
2- 2
Ammonium NH4
+ 1 Bromide Br− 1
Calcium Ca2+ 2 Carbonate CO3
2- 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

11. 1.Write the symbols of the elements which form a
compound.
If we have to write the formula of hydrogen
sulphide. First write down the symbols of
hydrogen and sulphur.
Symbols: H S

12. 2. Below the symbol of each element, write down its
valency.
Symbols: H S
Valencies: 1 2

13. 3.Finally cross-over the valencies of the
combining atoms. This will give the required
formula.
Symbols: H S
Valencies: 1 2

14. 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