U1-3-3 - Bonding and Attractions in Elements

Question 1

Why do covalent networks have high m.p./b.p.?

Answer 1

Strong covalent bonds are broken to melt/boil them, this requires a lot of energy.

Question 2

What are fullerenes?

Answer 2

Molecular forms of carbon, e.g. C₆₀

Question 3

Intermolecular forces/van der Waals forces

Answer 3

Forces (attractions) between molecules

Question 4

Forces of attraction between
temporary dipoles and induced dipoles.

Answer 4

London dispersion forces

Question 5

What causes temporary dipoles to form in atoms and molecules?

Answer 5

Any one of:

uneven distribution of electrons

electron cloud ‘wobble’

movement of electrons in the molecule

Question 6

LDF strength increases as …

Answer 6

the no. of electrons increases.

Question 7

London dispersion forces

Answer 7

Forces of attraction between
temporary dipoles and induced dipoles.

Question 8

Oxygen atoms have 8 electrons, neon atoms have 10 electrons.

Neon atoms have more electrons, but LDFs are stronger in oxygen. Why?

Answer 8

Oxygen is diatomic (O₂) and oxygen molecules have more electrons (16) than neon atoms (10).

Question 9

In covalent molecular substances, the boiling and melting point depend on …

Answer 9

… the strength of intermolecular forces.

(stronger forces = higher b.p./m.p)

Question 10

What is wrong with this statement?

“When water boils, covalent bonds are broken.”

Answer 10

Water is covalent molecular - only weak van der Waals forces are broken, not strong covalent bonds.

Question 11

What is wrong with this statement?

“When boron boils, covalent bonds are broken.”

Answer 11

Nothing - boron is a covalent network, so covalent bonds are indeed broken.

Question 12

Structure of noble gases

Answer 12

Monatomic

They exist as single atoms