IONIC BOND

Compounds formed by combining ions in such a ratio that the compound possess no electrical charge is known as ionic compound and its bond is known as ionic bond.

Ions are atoms with electric charge.

Ions that have less electrons than protons in them are said to have a net positive charge and are called cations, whereas ions than have more electrons than protons in them are said to have a net negative charge and are called anions.

POSITIVE ION

When an atom of an element loses

electrons from its outermost shell, it forms

a positive ion.

For example. Atomic number of sodium is

11 and so its electronic configuration is

(2,8,1).

If the number of electrons in the outermost orbit

of an atom are 1, 2 or 3, the atom tends to lose

electrons and forms positive ions.

Thus, Sodium atom will lose 1 electron in its

outermost orbit shell, form positive ion and

attain octet configuration 2,8 similar to that of

inert gas neon.

NEGATIVE ION

When an atom of an element gains electrons

from its outermost shell, it forms a negative ion.

For example. Atomic number of chlorine is 17

and so its electronic configuration is (2,8,7).

If the number of electrons in the outermost orbit

of an atom are 5, 6 or 7, the atom tends to gain

electrons and forms negative ions.

Thus, Chlorine atom will gain 1 electron in its

outermost orbit shell, form negative ion and

attain octet configuration 2,8,8 similar to that of

inert gas argon.

IONIC BOND IN NaCl

When sodium and chlorine come in contact,

each Na atom gives up an electron to become

a Na+ ion and Cl atom gains one electron to

become a Cl- ion.

So NaCl formed will have no net charge.

NaCl is the common salt that we use daily. It is

in ionic form even in solid state.

Ionic bond is formed is formed because of

strong attraction forces oppositely charged

ionic and closed electronic configuration

between Na+ and Cl.

Na+ and Cl ions are attracted by their nucleus

and form ion pair Na+Cl-.

MAGNESIUM CHLORIDE

Since Magnesium's atomic number is 12, its

electronic configuration is (2,8,2).

Hence, Magnesium is placed in group 2 and

period 3.

Magnesium has 2 valence electrons in it and

so it will tend to lose them, achieve octet

configuration of nearby inert gas and for

magnesium ion (Mg2+)

On the other hand, two chlorine atoms (2,8,7) will accept each of these electrons liberated by magnesium and form two Cl- ions. Thus, Chlorine will attain an octet configuration of (2,8,8).

MAGNESIUM OXIDE

Magnesium element (2,8,2) loses two electrons and forms magnesium ions Mg2+ .

Similarly, oxygen atom (2,6) gains two electrons and forms oxide ions (O2-).

When Mg2+ and O2- ions come near each other, due to opposite electric charge and attraction, they form ionic bond and rise to magnesium oxide MgO.

CHARACTERISTICS OF ATOMS,

IONS AND MOLECULE

Sodium metal is highly reactive. It easily reacts

with oxygen (O2) of the air and forms sodium

oxide (Na2O). Na2O further reacts with water

and gives sodium hydroxide (NaOH).

Sodium metal is highly active because its

electronic configuration is (2,8,1) and so it has

tendency to lose one electron from its valence

orbit and thus form sodium ion (Na+).

Na+ attracts chloride ion (Cl-) which has a

negative charge. Thus, Na+ and Cl- combine

and form NaCl.

Even though individually Na+ and Cl- are

reactive and non-edible, when they combine by

bonding, they lose their original individual

properties and form NaCl i.e. common salt

which can be consumed without any harm.

Thus, bonding alters the properties of

elements.

CRYSTAL STRUCTURE OF NaCl

By looking at the center of structure, one can

see that the chloride (Cl-) ion is connected

with six positively charged sodium (Na+) ions.

Similarly, we can have sodium (Na+) ion at

centre connected with six negatively charged

(Cl-) .

Such a structure of NaCl is called lattice

structure.

The ions are arranged in three dimensions and

so this structure is called a three dimensional

structure.

It should be noted that more the energy

between the positive and negative ions, more

the energy will be released.

More the energy is released, more stable the

structure becomes.

Since Na+ and Cl- highly attract each other, the

energy of the crystal structure decreases and

stability increases.

PROPERTIES OF IONIC

COMPOUNDS

1. Physical Nature

Ionic compounds are obtained in solid form.

Due to strong electrostatic forces between ions

having electric charges, ions are hard and

brittle.

Due to repulsion of opposite ions in these

compounds and due to their brittle nature, they

easily break into small pieces on applying

pressure.

2. Solubility

If ionic substances are dissolved in polar solvents such as water, the attraction between the ions of the compound decreases. this makes ionic substances soluble in polar substances.

But these compounds are insoluble in non-polar organic solvents such as ether, carbon tetrachloride, benzene, etc.

Due to these reasons, ionic compound sodium chloride (NaCl), easily dissolves in water but not in carbon tetrachloride.

3. Melting Point and boiling point

Ionic compounds have crystalline structure.

In crystal structures, positive and negative ions

are joined strongly through their interactive

attraction forces.

As a result, more energy is required to break

the crystal structure.

Hence, compounds have high melting and

boiling points.

4. Electrical conductivity

Ionic compounds are electrically neutral

because there are no unpaired electrons in the

positive ions in their crystal structure.

Thus, ionic solid compounds are bad

conductor of electricity.

But these compounds lose their neutral

characteristics in aqueous solutions and get

ionised. Hence, in aqueous or molten

solutions, ionic compounds conduct electricity.