Chemical bonding 4

Question 1

Why dipole moment of H halides decreases from HF and HI?

Answer 1

The electronegativity of halogen atom decreases form HF to HI so the polarity decreases hence dipole moment also decreases.

Question 2

How does VB theory vary from Lewis concept?

Answer 2

• According to VB theory, covalent bond is formed by the overlapping of half filled atomic orbitals containing electrons with opposite spin.
• According to Lewis concept, covalent bond is formed by mutual sharing of electrons.
• VB theory explains the shape of molecules while Lewis concept does not.

Question 3

Conditions for the combinations of atomic orbitals

Answer 3

• The combining atomic orbitals must have the same or nearby the same energy.
• 1s can combine with another 1s orbitals but cannot combine with another 2s orbital.
• The combining atomic orbitals must have the same symmetry about the molecular axis.
  EG:- 2pz can combine with another 2pz but not 2pz or 2px
• The combing atomic orbitals must overlap to the maximum extent. Greater the overlap, greater will be the electron density between the nuclei of molecular orbitals.

Question 4

Define EC

Answer 4

The distribution of e-s among various MO is called EC

Question 5

STABILITY OF MOLECULES

Answer 5

Na>Nb; unstable
Na<Nb; stable
Na=Nb; unstable

Question 6

Diamagnetic

Answer 6

If all the MO in a molecule is doubly occupied, the substance is diamagnetic (repelled by the magnetic field)

Question 7

Paramagnetic

Answer 7

If all the MO in a molecule is singly occupied, the substance is paramagnetic. (attracted by the magnetic field)

Question 8

Cause of the formation of Hydrogen bonds

Answer 8

The hydrogen atom bonds with electronegative atom. Due to thos, the H atom will have a partial +ve charge while the electronegatic atom will have a partial -ve charge. This results in the formation of a polar molecule having electrostatic force of attraction which can be represented as:
+…-….+…-….+..-
H-X….H-X….H-X

Question 9

Why HF has a higher BP than HCl?

Answer 9

In HF, there is H bonds but in HCl, there is no H bonds

Question 10

Why ethyl alcohol is completely miscible with water?

Answer 10

because ethyl alcohol forms hydrogen bond with water

Question 11

why p.nitrophenol has higher BP than o.nitrophenol?

Answer 11

cause of intermolecular hydrogen bond in p.nitrophenol.

Question 12

WHy glucose and fructose and sucrose are soluble in water though they are covalent compounds?

Answer 12

they have polar OH group which can form H bond in water

Question 13

Phosphorus pentachloride dissociates in the vapour phase according to the equation:
PCl5→PCl4+Cl-
What is the hybridization and geometry of PCl5 and PCl4+

Answer 13

PCl4+ is isostructural with NH4+, it will undergo sp3 hybridization as NH4+ undergoes sp3 hybridization.

Question 14

Which is more stable H2+ or H2-

Answer 14

The e- present in the ABO of H2- will de-stabilize the molecule.