6 Electronegativity, Bond Polarity And Intamolecular Forces

Question 1

Describe the covalent bond in a molecule of an element

Answer 1

Each atom has an equal share of the electrons in the bond. It is a 100 % covalent bond

Question 2

Describe what happens when bonding atoms are different

Answer 2

• nuclear charges different
• atoms may be different sizes
• Shared pair of electrons may be closer to nucleus of one atom

One of the atoms is likely to attract the bonding electrons more

Question 3

Definition of electronegativity

Answer 3

A measure of the attraction of a bonded atom for the pair of electrons in a covalent bond

Question 4

What is a non polar bond

Answer 4

• bonded pair shared equally between bonded atoms
• atoms have the same or similar electronegativity
• called pure covalent bonds
  Eg C-H

Question 5

What is a polar bond

Answer 5

• bonded electron pair shared unequally between the bonded atoms
• happens when bonded atoms are different and have different electronegativity
• the more electronegative atom has a greater attraction for the bonded pair of electrons

Question 6

Define permanent dipole

Answer 6

A small charge difference across a bond that results from a difference in the electronegativities of the bonded atoms

Question 7

What does a polar covalent bond contain

Answer 7

A permanent dipole

Question 8

What makes a polar molecule a polar molecule

Answer 8

Is not symmetrical and bind dipoles don’t cancel out

Opposite for a non polar molecule ( you can have a non polar molecule with polar bonds)

Question 9

Define polar molecule

Answer 9

Has an overall dipole when you take into account any dipoles across the bonds

Question 10

Polar molecules can dissolve ……
Non polar molecules can dissolve ……

Answer 10

Polar molecules
Non polar molecules

Question 11

What is the scale to measure electronegativity called and when was it invented

Answer 11

Pauling scale in 1932

Question 12

Factors affecting electronegativity

Answer 12

Nuclear charge- more protons = more attraction between bonding electrons and nucleus
Distance from the nucleus- smaller radius= stronger attraction. Bonding pair closer to nucleus
Electron shielding- less electron shells between nucleus and bonding pair = stronger attraction

Question 13

What makes a bond a non polar covalent, polar covalent or ionic

Answer 13

NPC= no difference between electronegativity
PC= small difference in electronegativity
I= large difference in electronegativity

Question 14

What are the ranges in electronegativity that cause the type of bond to change
Roughly

Answer 14

Difference is bigger than 1.7 = ionic
Difference is between 1.7 and 0.5 = polar covalent
Difference is less than 0.5 = pure covalent (non polar covalent)

Question 15

Explain why electronegativity increase across a period

Answer 15

• atomic radius decreases
• more nuclear charge (protons)
  Therefore stronger attraction between nucleus and bonding pair

Question 16

Explain why electronegativity decreases down a group

Answer 16

• atomic radius increases
• more shielding
  Therefore less attraction between the nucleus and bonding pair

Question 17

What are intermolecular forces

Answer 17

Weak
Interactions between dipoles of different molecules
Caused by weak attractive forces between small dipoles in different molecules

Question 18

3 types of intermolecular forces and their relative strengths

Answer 18

Weakest London forces
Permanent dipole dipole interactions
Strongest Hydrogen bonding

Question 19

What are London forces

Answer 19

They exist between all molecules
Weak attractions between small TEMPORARY dipoles in NEIGHBOURING molecules

Question 20

How do London forces increase in strength

Answer 20

With the number of electrons increasing

Question 21

What are the only attractive forces acting in non polar molecules

Answer 21

London forces

Question 22

Permanent dipole dipole interactions

Answer 22

Polar molecules have them
The permanent dipole of one molecule attracts the permanent dipole in another forming a weak permanent dipole-dipole force

Question 23

Where are hydrogen bonds found

Answer 23

Between molecules containing
- a strong electronegative atom with a lone pair of electrons ( O, N, F)
- a hydrogen atom attached to the O, N or F

The slightly positive hydrogen on one molecule attracts to a lone pair of electrons on a different molecule

Question 24

Rules for drawing hydrogen bond

Answer 24

Dotted line
From the lone pair to the hydrogen

Question 25

How does hydrogen bond effect the boiling point of water

Answer 25

Without it it would be much lower and there would be no liquid water on earth

Question 26

Properties of water

Answer 26

1) ice less dense than water
- H bonds create open lattice- big gaps make it less dense
2) water has high MP and BP
- H bonds are extra forces on top of London forces
3) high surface tension
- due to raft of H bonds