Classification of Elements and Periodicity in Prop

3.13. A cation is obtained by removing an electron from the outermost shell. The removal of electron (s) results in decrease of the size of the resulting ion than the parent atom because it has fewer electrons while its nuclearcharge remains the same.

Anions are obtained by addition of electron (s) in the outermost shell. This results in increased repulsion among the electrons and a decrease in effective nuclear charge.

3.12.  (a) All of them have 10 electrons each and are isoelectronic in nature.

(b) In isoelectronic species, higher the nuclear charge, smaller will be the atomic or ionic radius.

Al³⁺< Mg²⁺< Na⁺< F^–< O^2-< N^3-

3.11. Species (atoms/ions) which have same number of electrons are called isoelectronic species. The isoelectronic species out of the given atoms/ions are:

(i) Na⁺ is isoelectronic to F^- 

(ii) K⁺ is isoelectronic to Ar

(iii) Na⁺ is isoelectronic to Mg²⁺

(iv) Sr²⁺ is isoelectronic to Rb⁺

3.10. Across a period, the atomic radii decrease from left to right due to increase in effective nuclear charge from left to right across a period

Within a group, atomic radius increases down the group due to continuous increases in the number of electronic shells or orbit numbers in the structure of atoms of the elements down a group.

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.