Questions - Answers

2 Marks Questions

1. Among N^-3, O^-2, F^-, Na⁺, Mg⁺² and Al⁺³

a) What is common in them?

b) Arrange them in the increasing ionic radii.

A: a) All the ions are having same number of electrons and are called "isoelectronics".

b) Order: Al⁺³< Mg⁺²< Na⁺< F^-< O^-2< N^-3

2. First ionization enthalpy (IE₁), of O is less than that of N. Explain.

A:  N has 1s² 2s² 2p_x¹ 2p_y¹ 2p_z¹ electronic configuration. As 2p orbitals are half filled, N is more stable and requires more energy to remove an electron from it. So IE₁ of O is less than that of  N.

3. What is diagonal relationship?

A:  The phenomenon of exhibiting similar properties by second period elements with the 3rd period elements of next group's known as diagonal relationship. (Due to similar electronegativity and ionic size)

e.g.: Li & Mg, Be & Al are diagonally related.

4. Mg⁺² is smaller than O^-2 in size, though both have same electronic configuration. Explain.

A:  Mg⁺² and O^-2 are isoelectronics. Due to more nuclear charge (more number of protons) in Mg⁺² has more attraction with the valence electrons. So Mg⁺² is smaller in size than O^-2.

4 Marks Questions

1. What is electronegativity? How does it vary in a group and in a period?

A:  The relative tendency of an atom in a covalent compound to attract the shared pair of electrons more towards itself.

In a group: E.N. Decreases from top to bottom.

In a period: E.N. Increases from left to right.

2. What is lanthanide contraction? What are its consequences?

A:  The steady decrease left to right in atomic size of lanthanides due to poor shielding effect and diffused shape of f orbitals is called lanthanide contraction.

Consequences:

1) Due to similar crystal structure and properties, it is difficult to separate lanthanides from their mixture.

2) 4d and 5d series of elements have more similarities in properties.

e.g.: Zr & Hf