MR - Electronegativity and Intermolecular Forces

Question 1

Define electronegativity

Answer 1

The ability to attract bonding electrons in a covalent bond

Question 2

What scale is electronegativity measured on and what do higher values mean?

Answer 2

The Pauling scale

The higher the value, the more electronegative the element is

Question 3

State the most electronegative element

Answer 3

Fluorine

although Oxygen, Nitrogen and Chlorine are also strongly electronegative

Question 4

Describe the trend in electronegativity across the periods

Answer 4

Electronegativity increases across the periods

Question 5

Describe the trend in electronegativity down the groups

Answer 5

Electronegativity decreases down the groups (ignoring noble gasses)

Question 6

Explain polarity of covalent bonds

Answer 6

In a covalent bond between two atoms of different electronegativities, the bonding electrons are pulled towards the more electronegative atom. This makes the bond polar

Question 7

Explain why a molecule’s shape and polarity effect whether it has a permanent dipole

Answer 7

• Simple molecules (like HCl), polar bonds give the whole molecule a permanent dipole
• More complicated molecules may have several polar bonds. If they are arranged so they point in opposite directions, they’ll cancel each other out (non-polar overall)
• If the polar bonds all point in roughly the same direction, then the molecule is polar
• Lone pairs of electrons on the central atom also have an effect on the overall polarity

Question 8

Name the 3 types of intermolecular bonds

Answer 8

• Permanent Dipole - Permanent Dipole
• Instantaneous Dipole - Induced Dipole
• Hydrogen Bonding

Question 9

Give the 3 types of intermolecular bonds in order of strength from strongest to weakest

Answer 9

• Hydrogen
• PD-PD
• ID-ID

Question 10

Describe PD-PD bonding

Answer 10

The delta + and - charges on polar molecules cause a weak electrostatic force of attraction between molecules

Question 11

Describe ID-ID bonding

Answer 11

• Electrons in charge cloud are always moving quickly. At one moment, the electrons in a bond are more likely to be one side than the other
• This dipole can induce a temporary dipole in adjacent molecules. The molecules are then attracted to each other
• Because the electrons are constantly moving, dipoles are being created and destroyed all the time.

Question 12

Give 3 factors that effect the strength of intermolecular forces

Answer 12

• The polarity of the molecules
• The size of the molecule
• The shape of the molecule (e.g. branching)

Question 13

Describe hydrogen bonding

Answer 13

• Hydrogen is bonded to an electronegative element drawing the bonding electrons away from Hydrogen
• This bond is polarised so Hydrogen forms an electrostatic attraction to a lone pair of electron of other molecules