Chemistry

3.9. Atomic radius: It is the distance from the centre of nucleus to the outer most shell of electrons in the atom of any element. It incorporates both the covalent, metallic radius or van there Waal's radius depending on whether the element is a non-metal or a metal.

Ionic radius: It is the distance between the centre of the nucleus of an ion up to the point where it exerts its influence on the electron cloud of a canton or anion.

3.8. The elements in a group have same number of valence electrons and hence have similar physical and chemical properties.

3.7.  (i) Lawrencium (Lr) with atomic number (z) = 103

(ii) Seaborgium (Sg) with atomic number (z) = 106.

3.6. The element is chlorine (Cl) with atomic number (Z) = 17.

3.5. Elements with atomic numbers from Z = 87 to Z = 114 are present in the 7th period of the periodic table. So, this elements lies in the Period – 7 and Group -14 of Block-p.

3.4. The sixth period means that the highest principal quantum number = 6. The subsequent periods comprise of 8, 18, 18 and 32 elements in the same order. The sixth period comprises of 32 elements where electrons enter the 6s, 4f, 5d and 6p orbitals. Number of orbitals present in 6s=1. 4f= 7, 5d= 5 and 6p= 3. The total number of orbitals is 16. A total of 32 electrons can be filled in these 32 orbitals; therefore, the sixth period should have a maximum of 32 elements.

3.3. Mendeleev's periodic law classifies the elements based on their atomic weight. Modern periodic law classifies the elements based on their atomic number.

3.2. Mendeleev arranged the elements horizontally, in periods and vertically, in groups in the increasing order of their atomic masses. This classification was done in such a way that the elements with similar properties fall in the same group.

3.1. The basic theme of organisation of elements in the periodic table is to simplify, systematize and classify the elements based on their similarities in properties. This arrangement makes it easier for us to group the elements and makes it less confusing to present the periodic table.

1.20 ZnS shows Frenkel Defect.
AgBr shows Frenkel Defect and Schottky Defect. Frenkel Defect: It is a kind of defect in crystalline solids in which atoms are displaced from their lattice position 
to interstitial site creating vacancy at the lattice point. It usually occurs in ionic solid with large difference in size 
of ions.
Schottky Defect: This defect occurs when oppositely charged ions leave their lattice site creating vacancies in 
such a way that electrical neutrality of crystal is maintained. It is generally seen in highly ionic compounds where 
difference in size of cation and anion is small.