Grade 11 - Chemistry - Chemical Bonding Moecular Structure - Electrovalent or Ionic Bond
Electrovalent or Ionic Bond:
a) Elements of low ionization potential interact with elements of high electron affinity always form ionic bond
b) Bond formed in the process of loosing and gaining electrons by the interacting atoms of different elements, changing to ions
c) Oppositely charged ions are held together within optimum distance through electrostatic force of attraction
d) This bond force is known as electrovalent or ionic bond force
e) Electrovalent bond is not possible between similar atoms
Conditions for forming Ionic Bonds
a) Atoms having electrons 1,2 or 3 act as donor and changes into stable cation of respective charges; whereas atoms having valency electrons 5,6 or 7 act as electron acceptor and changes into stable anions
b) Atoms having 1,2 or 3 valency electrons are elements of low ionization potential and atoms having 5,6 or 7 valency electrons are elements of high electron affinity
c) Atoms changing into cations should be large in size, whereas atoms changing into anions should be small in size
d) There should be a difference of 1.9 in electronegativity of the combining atoms
e) Energy must be released while bond formationIn the formation of NaCl
Here as the difference in the value of I.E. and E,A. increases, there is more tendency to form cation and anion, consequently more favourable for formation of ionic or electrovalent bond
i) Gaseous ions while held through electrostatic force of attraction in the ionic lattice; whereby releases energy, known as lattice energy
Ii) Higher the lattice energy greater will be the ease of formation of Electrovalent compound
iii) Lattice energy will be high in the case of small size and high charge ions
Characteristics of Ionic Compounds
a) Ionic or electrovalent compounds are solid crystalline compounds , held in crystalline lattice
b) Forces operating in such compounds are operating in all directons
High melting and boiling points:
Melting and boiling points of ionic compounds are excessively high due to strong electrostatic force of attraction operating between the oppositely charged ions and as well as they are strongly held in crystall lattice
a) Ionic compounds in the solid state cannot conduct electricity as they strongly held in the crystalline lattice
b) In the fused state or in solution of such compounds , good conductor of electricvity
Ionic solids dissolve in polar solvents to dissociate into component ions, which are responsible for ionic reactions.
a) Ionic or electrovalent compounds are normally soluble in polar solvents and insoluble in non-polar solvents.
b) This solubility is due to ion dipole attraction. e.g. Na+ ion is attracted by water dipole created between O---H group.
c) The solubility of an ionic compound in polar solvent can be best explained on the basis of lattice energy and hydration energy.