Exam Q 29

Question 1

Define electronegativity

Answer 1

Electronegativity is the relative attraction that an atom in a molecule has for the shared pair of electrons in a covalent bond

Question 2

Account for the difference in bond angles between the two molecules with 109.5 degrees in SH4 and 107.3 degrees in ammonia (NH3)

Answer 2

account: NH3 has 1 set of lone pairs and 3 bond pairs while SiH4 has no lone pairs and 4 bond pairs.
The repelling force between the lone pair and bond pairs in NH3 are stronger than the bond pair-bond pair repullsion in SiH4 reducing the size of NH3 bond angles.

Question 3

Use electronegativity values to determine which bond, N-H bond in ammonia or the Si-H bond in silane, is the more polar

Answer 3

electronegativity of H = 2.20, N = 3.04, Si = 1.90
3.04-2.20=.84
2.20-1.90=.30
The N-H bond is more polar

Question 4

Which of the two molecules has hydrogen bonding between its molecules? Justify your answer

Answer 4

Ammonia as hydrogen bonding only occurs with nitrogen, oxygen or fluorine which are all small and highly electronegative atoms

Question 5

Give the reason why a molecule with polar bonds can be non-polar

Answer 5

The centres of positive and negative charges in the molecule coincide and the dipole moments cancel