Page 47 - Chemistry ICSE Class X

Chemical Bonding 35
Electrovalent (or Ionic) Compounds

What are electrovalent (ionic) compounds
#P GNGEVTQXCNGPV QT KQPKE EQORQWPF OC[ DG FGſPGF CU HQNNQYU
The compound formed due to the transfer of electrons from the
atom of an element to that of another is called an electrovalent (or ionic)
compound.
Some typical electrovalent (or ionic) compounds are
–
+
ƒ Sodium chloride Na Cl or simply as NaCl
+
ƒ Potassium sulphate (K ) SO 4 2– or simply as K SO 4
2
2
2+
–
ƒ Calcium chloride Ca (Cl ) or simply as CaCl 2
2
During the formation of electrovalent (or ionic) compounds, the
element whose atom loses electrons is said to be oxidised, and the element
whose atom gains electrons is said to be reduced.
What are the characteristics of ionic compounds
Some important characteristics of electrovalent (or ionic) compounds are
described here.
ƒ *CTF CPF TKIKF Electrovalent (or ionic) compounds are hard and rigid
due to strong coulombic forces between the oppositely charged ions.
ƒ *KIJ FGPUKV[ Electrovalent (or ionic) compounds have relatively
high density. In ionic compounds, the ions are closely packed. This
decreases volume of the system, and as a result density is high.
ƒ State of existence. Crystalline nature. In electrovalent (or ionic)
compounds, ions are arranged in a regular geometrical fashion. This
orderly distribution of ions give characteristic geometrical shapes to
the crystals of electrovalent (or ionic) compounds.
ƒ *KIJ OGNVKPI CPF DQKNKPI RQKPVU Due to strong coulombic force of
CVVTCEVKQP VJG KQPU CTG DQWPF VQ GCEJ QVJGT XGT[ ſTON[ #U C TGUWNV VJG
electrovalent (or ionic) solids have high melting and boiling points.
ƒ Electrical conductivity. Solid electrovalent (or ionic) compounds do
not conduct electricity. This is because in the solid state, the constituent
KQPU CTG ſZGF VQ VJGKT RQUKVKQPU KP VJG NCVVKEG
The electrovalent (or ionic) compounds, however, conduct electricity
when dissolved in solvents like water or when melted. This is because
the ions get free in the solution or in the melt. These free ions move
freely in the solution or melt, and conduct electricity.
ƒ Thermal conductivity. Electrovalent compounds have low thermal
conductivity.
ƒ Solubility. Electrovalent (or ionic) compounds dissolve easily in
polar solvents, such as water, but do not dissolve in nonpolar organic
solvents, such as benzene, carbon tetrachloride, etc.
ƒ Dissociation. Electrovalent (or ionic) compounds when dissolved in
solvents like water, or when melted, dissociate to give free ions. For
example, sodium chloride when dissolved in water gives sodium and
chloride ions, viz.,
–
+
dissociation
+
–
Na Cl (s) + H O(l) ⎯⎯⎯⎯⎯→ Na (aq) + Cl (aq)
2
sodium chloride sodium ion chloride ion
+
–
+
–
melted
Na Cl (s) ⎯⎯⎯→ Na Cl (l) o Na + + Cl –
sodium chloride molten sodium chloride