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Ionic Bonding

 

Ionic bonding, also known as electrovalent bonding occurs between two atoms, such that one of them is readily able to lose electrons (atom of low ionization energy and high electropositivity) to form positively charged ion which is isoelectronic with the inert gases, while the other readily accepts the lost electrons (atom of high electron affinity and high electronegativity) to form negatively charged ion which is isoelectronic with the noble gases.

The two charged particles are then held together by strong electrostatic force of attraction (this is the bond) to form the compound, which is ionic. This type of bonding is formed between metal atoms (members of groups IA, IIA and IIIA) and atoms of non - metals (groups VA, VIA and VIIA).

For example:

1. Formation of NaCl: An atom of Na (group IA) of electronic configuration 1s22s22p63s1 can easily lose the one electron in its outermost shell, i.e., 3s1 to become isoelectronic with the inert gases, i.e., 1s22s22p6 and thus be stable. Na → Na+ + e-

An atom of Cl (group VIIA) of electronic configuration 1s22s22p63s23p5 can easily gain the electron to add to the seven already in its outermost shell, i.e., 3s23p5 to become isoelectronic with the inert gases, i.e., 1s22s22p63s23p6 and thus be stable.

Cl + e- → Cl- Hence, the two oppositely charged particles (Na+ and Cl-) are balanced, and are brought together by strong electrostatic force of attraction, forming the compound.

Na+ + Cl- → NaCl

2. Formation of MgCl2:

An atom of Mg (group IIA), 1s22s22p63s2 can easily lose the two electrons in its outermost shell, i.e., 3s2 to become isoelec- tronic with the noble gases, and thus stable. Mg → Mg2+ + 2e-

The two electrons are gained by two atoms of chlorine (since one atom of Cl needed one electron to be stable).

2Cl + 2e- → 2Cl-

Both Mg2+ and 2Cl- are balanced, and are then held together by strong electrostatic force of attraction.

Mg2+ + 2Cl- → MgCl2

3. Formation of Na2O:

Two atoms of Na can easily lose one electron each 2Na → 2Na+ + 2e-

One atom of oxygen (group VIA), 1s22s22p4 can easily gain the two electrons to add to the six in its outermost shell, i.e., 2s22p4 and become isoelectronic with the noble gases, i.e., 1s22s22p6 , and thus be stable .

O + 2e- → O2-

Both ions are balanced, and are then held together by strong electrostatic force of attraction, forming the compound.

2Na+ + O2- → Na2O

4. Formation of Al2O3

An atom of Al (group IIIA), 1s22s22p63s23p1 can lose the three electrons in its outermost shell, i.e., 3s23p1 to be isoelectronic with the noble gases and thus be stable. Al → Al3+ + 3e-

An atom of oxygen as we have shown can take in two electrons to be stable. O + 2e- → O2-

Therefore, to balance the charges, two atoms of Al are needed to provide six electrons, which are gained by three atoms of oxygen.

2Al → 2Al3+ + 6e- ; 3O + 6e- → 3O2-

The two oppositely charged particles are then held together by strong electrostatic force of attraction to form the compound. 2Al3+ + 3O2- → Al2O3

Note:

* The higher the electropositivity of the metal and electronegativity of the non - metal involved in the union, the greater the strength of the electrovalent bond between them. Hence, the greater the ionic character of the compound formed.

* The number of electrons lost by the metal atom(s) is completely accepted by the atom(s) of the non-metal, so that the charges are balanced.

Properties of Ionic Compounds

1. They are solids and have high melting and boiling points.

2. They are good conductors of electricity.

3. They are soluble in ionic or polar solvents.

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