Simple Covalent Molecules & Intermolecular Forces - Structure & Properties (2.2)

Question 1

Give an example of a specific type of dipole-dipole interaction

Answer 1

Hydrogen bonding (an extreme example of dipole-dipole interaction)

Question 2

What elements can H bond to in hydrogen bonding?

Answer 2

F, O or N

Question 3

How does hydrogen bond donor bond?

Answer 3

H bonded directly to F, O or N

Question 4

How does hydrogen bond acceptor bond?

Answer 4

Lone pair of electrons on F, O or N

Question 5

What happens if two atoms have the same electronegativity values?

Answer 5

The electrons lie directly in the middle of the bond & it is non-polar

Question 6

Describe London forces briefly

Answer 6

Random fluctuations in electrons can produce temporary dipoles

Question 7

Give the 3 other names for London forces

Answer 7

Dispersion forces
Induced dipole-induced dipole interactions
Temporary dipole-dipole

Question 8

Explain how London forces occur between molecules

Answer 8

• The temporary dipole induces a dipole in a neighbouring molecule
• A dipole-dipole interaction is formed momentarily & then disappears

Question 9

Give two factors that affect the strength of London forces and how they affect London forces

Answer 9

• The size of the molecule
• The number of electrons

Both increase the chance of an uneven distribution of electrons & stronger London forces

Question 10

What type of molecules do London forces occur between?

Answer 10

All molecules

Question 11

What type of molecules do dipole-dipole interactions occur between?

Answer 11

Molecules that have a permanent dipole

Question 12

What type of molecules do hydrogen bonds occur between?

Answer 12

Molecules with a H bond donor and a H bond acceptor

Question 13

Do giant covalent lattices have high/low melting points? Explain why

Answer 13

• Giant covalent lattices have v. high melting points

- Covalent bonds are v. strong & require a lot of energy to be broken

Question 14

What happens to the forces & bonds when simple covalent molecules melt/boil?

Answer 14

The covalent bonds do NOT break and the molecule remains intact BUT the weak intermolecular forces between the molecules break

Question 15

Explain what intermolecular forces are (in terms of interaction between molecules)

Answer 15

Intermolecular forces are the attractive or repulsive forces between slightly positive & slightly negative ends of a molecule

Question 16

Give the 3 main types of intermolecular force

Answer 16

1. Permanent dipole-dipole interactions
2. Hydrogen bonds
3. London forces

Question 17

How is an electron cloud created?

Answer 17

Electrons can move all around the surface of the molecule

Question 18

What makes a molecule non-polar?

Answer 18

When electrons are evenly spread within the molecule

Question 19

What makes a molecule polar?

Answer 19

• When electrons are unevenly spread to give a dipole
• One side is slightly more positive (less electrons)
• The other side is slightly more negative (more electrons)

Question 20

What is electronegativity?

Answer 20

The power of an atom to attract electron density from inside a covalent bond
(if an atom is more electronegative than the other, it is more negative, therefore it attracts more electrons)

Question 21

Why do permanent dipoles occur?

Answer 21

Due to differences in electronegativity

Question 22

What factors affect electronegativity?

Answer 22

• Atomic radius
• Nuclear charge
• Shielding

Question 23

What is the trend in electronegativity across periods in the periodic table?

Answer 23

Electronegativity increases across periods

Question 24

What is the trend in electronegativity down groups in the periodic table?

Answer 24

Electronegativity decreases down groups

Question 25

Why is a BOND polar?

Answer 25

When there is a significant difference in electronegativity values

Question 26

Give 3 examples of polar bonds

Answer 26

C-N
C-O
C-F
C-Cl
C-Br
O-H
N-H
X-H (X is any halogen)

Question 27

Give an example of a bond that is not polar

Answer 27

C-H

Question 28

Explain how dipole-dipole forces occur between molecules

Answer 28

The molecules align so that the δ+ ends are attracted to the δ- ends of a neighbouring molecule

Question 29

How does size of the dipole affect the interaction?

Answer 29

The larger the dipole, the stronger the dipole-dipole interaction