Ionic solids vs Covalent solids

Solids can be classified as Ionic solids, covalent network solids, metallic solids and molecular solids.

1. SOLIDS XI FDC CHEMISTRY SIDRA JAVED

2. IONIC SOLIDS A n ionic crystal is formed due to the transference of electrons from one atom to the other. The C ations and Anions formed are held together through strong electrostatic forces.

3. Formation of NaCl Sodium loses one electron to be converted into Na + ion Na  Na + + 1e - Chlorine gains one electron to be converted into Cl - ion Cl + 1e -  Cl - These ions combine together due to strong electrostatic attraction forces Na + + Cl -  NaCl ∆H = -786 KJ/ mol

4. Crystal lattic of NaCl

5. Covalent network solids The crystalline solids in which atoms of similar or dissimilar elements are held together in a network of single bond are known as covalent crystals or covalent network solids.

6. Formation of Covalent crystals i . When covalent bonds give giant molecules. ii. When atoms join together by covalent bonds and as a result separate layers are formed.

7. Comparison between Ionic and Covalent Solids Ionic Solids Ionic solids are non conductors of electricity in their solid state. However they conduct electricity in the molten or solution form. Ionic solids have definite geometric shape. They are non-directional in nature. They do not exist in molecules due to their ionic nature. Covalent network solids They are bad conductors of electricity with the exception of graphite. They have definite shape and oriented in 3D with network structure. They have open structures due to valences of atoms directed in definite directions. They may be called as molecules due to their covalent nature.

8. Low density of ice When the temperature is decreased the molecules come close to each other. As a result the intermolecular attractive forces increase. However some empty spaces are developed in the ice. As a result about 9% more spaces than liquid water are produced. As the density is inversely proportional to volume, the increase in volume decreases the density. That is why ice floats over water.

9. Applications of low density of ice in real life In cold countries when the temperature is decreased to 0 o C, water in ponds and lakes freezes. A thick layer of ice is formed that stays at the top. This layer of ice acts as insulator for further heat loss. Fish and plants can survive in the water for months under the thick blanket of ice.

10. High heat of fusion of ice The quantity of heat required to convert one mole of a solid into liquid is called molar heat of fusion. Molar heat of fusion for ice is +6.02 KJ/ mol Ice (solid)  Water (liquid) ∆H = 6.02 KJ/ mol

11. Application of high heat of fusion of ice in daily life Ice absorbs 0.333 KJ of energy for every gram of ice to melt. To melt 100 gram of ice, 33.3 KJ of energy is required. It means if 33.3 KJ of energy from the surrounding is absorbed by each of the drink, the temperature of the drink without ice would rise from 0 o C to 20 o C. The drink containing the ice would remain at 0 o C but 100 gram of ice would melt.

12. Hygroscopic salts Some salts absorbs moisture from atmosphere. Such salts are called hygroscopic salts. CaCl 2 has the ability to absorb moisture from atmosphere. Thus it becomes hygroscopic. The absorption of moisture becomes maximum when there is humidity in air. The water molecules absorbed will become part of crystal of CaCl 2 and may be called as water of crystallization. A salt containing water of crystallization is called hydrate. CaCl 2 can absorb a maximum of 2 water molecules there fore it becomes CaCl 2 .2H 2 O. The water of crystallization increase the mass of CaCl 2 .

13. How to get NaCl from saline solution? Saline water ( NaCl solution) contains water along wih certain impurities. If saline water is allowed to freeze in freezing mixture, the impurities come up to the surface in the form of ice at -3.4 o C leaving behind NaCl . Ice and impurities are removed from the surface leaving behind pure NaCl .

14. End of lesson s [email protected]