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.