Electronegativity, Polarity and Intermolecular Forces

Question 1

What is electronegativity?

Answer 1

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

Question 2

What factors affect electronegativity?

Answer 2

• Nuclear charge - more is more electronegativity

- Atomic radius - more is less electronegativity

Question 3

How does the Pauling scale work? (3)

Answer 3

• Atoms have values up to 4.0
• The higher up and to the right you go, the more electronegative atoms get
• F, O, N and Cl have highest electronegativity

Question 4

Why are some molecules polar?

Answer 4

Some atoms in the molecule are more electronegative than others

Question 5

How do you define a pure covalent bond?

Answer 5

Atoms of a molecule are the same element and so there is no difference in electronegativity and the electron pair is shared equally

Question 6

How do you define a permanent dipole?

Answer 6

The atoms of a molecule have a difference in electronegativity and so the one with higher EN pulls the bonded electron pair to itself and has a slightly negative charge

Question 7

How do molecules with dipoles have no overall charge?

Answer 7

Over the whole molecule, the dipoles cancel each other out and the overall charge is 0

Question 8

Why do some atoms dimerize?

Answer 8

Atoms can donate electron pairs.

e.g. AlCl3 -> Al2Cl6

Question 9

Why are hydrogen bonds formed?

Answer 9

An atom of a molecule with a slight negative charge attracts the slightly positive atom of another molecule

Question 10

How many hydrogen bonds can water form?

Answer 10

4

2 hydrogens and 2 lone pairs of electrons on O

Question 11

Why does water have high melting and boiling points?

Answer 11

• Hydrogen bonds are extra forces and there are a lot of them
• More energy is needed to break h-bonds in water
• In ice, lattice arrangement needs to break
• In water, the hydrogen bonds need to break completely

Question 12

Why does solid water float?

Answer 12

• H-bonds hold molecules apart in an open lattice structure

- Molecules are further apart so less dense than liquid

Question 13

How are london forces formed?

Answer 13

• Movement of electrons create instantaneous dipoles that are always shifting
• This induces dipoles on other molecules
• Positive and negative sides attract

Question 14

What affects the strength of london forces?

Answer 14

• More atomic radius means more electrons and weaker nuclear attraction - temporary dipoles more easily induced

Question 15

How are polar substances soluble in polar solvents?

Answer 15

Interactions between solvent + substance (positive and negative charges)

Question 16

What does polar solubility depend on?

Answer 16

• Strength of dipole - stronger means more soluble

e. g. ethanol has polar and nonpolar regions so it dissolves in both polar and nonpolar substances