Bond Polarity And Intermoleuclar Forces

Question 1

What is a permanent dipole ?

Answer 1

• when two atoms in a molecule have a large difference in their E.N
• more e.n = delta -
• less e.n = delta +

Question 2

Why does Argon has very low b.p ?

Answer 2

• it is small atomic radius = hard to polarise
  = produce small VDW forces = need less energy to overcome

Question 3

What element must contain for hydrogen bonding to occur?

Answer 3

• need a H atom and atoms with at least one lone pair e.g. N, O,F

Question 4

General trend of hydrogen halides HCl- HI

Answer 4

• b.p increase down the group
  Bec. Bigger molecule with more electrons as you go down = has larger temporary dipoles = larger VDW forces = need more energy to overcome

Question 5

Why does HF deviates from the trend of hydrogen halides ?

Answer 5

• F has a lone pair = hydrogen bonds formed
• H bond is stronger IMF than VDW or permanent dipole = need more energy to overcome = HF has the highest b.p

Question 6

Why ice is less dense than water that deviates from other solids.

Answer 6

• h bonds help molecules to be more spread out apart than in liquid water = need less energy to overcome the h bond force than in liquid water

Question 7

Definition of electro negativity

Answer 7

• the ability of atom to attract electrons towards themselves in a covalent bond

Question 8

What is a polar covalent bond?

Answer 8

• where e- distribution is unevenly shared of two atoms

Question 9

Why does CCl4 has polar bonds but not a permanent dipole ?

Answer 9

• they have partial charges but it is symmetrical = partial charges cancel each other out = non polar

Question 10

Why does water has high b.p than H2S ?

Answer 10

• water has h bonds but H2S doesn’t = need more energy to overcome.

Question 11

Trend of E.N going down the group

Answer 11

More charge, more shielding as atoms get bigger = harder to attract electrons
= the top has the greatest e.n

Question 12

Trends of e.n across a period

Answer 12

• more charge, same shielding = easier to attract electrons
  = E.N increases as you go -) a period

Question 13

What is a polar molecule ?

Answer 13

• atoms have large differences in e.n = electrons are unevenly distributed = create a dipole and partial charge don’t cancel out
• polar bonds arranged asymmetrically
• have permanent dipole

Question 14

What’s is a non polar molecule ?

Answer 14

• when atoms’ e.n are the same = e- distributed evenly = polar bonds arranged symmetrically
  = partial charge cancel out bec. It is a balanced distribution of electrical charge

Question 15

What caused Van de Waals forces ?

Answer 15

• electrons distribution changes = induce new dipoles around it = instantaneous dipole forces
  + attract to - pole

Question 16

VDW- b.p

Answer 16

Stronger VDW= higher b.p
Bec. More e- in the atom = greater Mr= grater instantaneous dipole forces = requires more energy to overcome

Question 17

Permanent dipole- dipole forces

Answer 17

• only act between two permanent dipole molecules
• the effect of polarity will cancel out in each bond when one molecule has more than one polar bond = leaving it with no dipole moments

Question 18

Solubility - IMF

Answer 18

• non polar molecules only dissolve in N.P substances e.g. H20
• polar molecules only dissolve in p. Substances e.g. PH3
  E.g. PH3 cannot is insoluble in H2O