Intermolecular forces and hydrogen boding

Question 1

What is a non polar covalent bond
give an example

Answer 1

No difference between electronegativity
H-H and Cl-Cl

Question 2

electronegativity

Answer 2

measure of tendency of an atom to attract a bonding pair of electrons in a covalent bond.

Question 3

polar covalent bond
give an example

Answer 3

difference in electronegativity H-Cl

Question 4

H-H and H-F
For each molecule above state whether they are polar or non polar and explain why.

Answer 4

H-H non polar. No difference in electronegativity as they are the same element.

H-F polar. Difference in electrongeativity

Question 5

What are the 3 common types of intermolecular forces

Answer 5

1. London forces
2. Induced dipole-dipole forces
3. Hydrogen bonds

Question 6

Would H2 molecules have permanent dipole-dipole interactions between them

Would HCl molecules have permanent dipole-dipole interactions between them?

Why or why not?

Answer 6

No. They have no permanent dipole as there is no difference in electronegativity. (non-polar)

Yes. They have permanent dipoles because there is a difference in electronegativity.(polar)

Question 7

lone pairs

Answer 7

pair of electrons occupying in an orbital (the electrons in the lewis structure)

Question 8

which intermolecular forces are these elements :
CO2
SF4
CH3NH3
explain why?

Answer 8

• CO2 has a london dispersion force because

Question 9

how do you know whether a compound is non-polar:

Answer 9

• central atom has no lone pairs
• all atoms around central atom is the same

Question 10

Melting and boiling points of water

Answer 10

• Water a higher melting and boiling point compared to other simple molecular substances
• Therefore at room temperature it is a liquid( while other tend to be gases)
• This is because water contains hydrogen bonding which is the strongest intermolecular force

Question 11

Explain why compounds with hydrogen of group 6 (O, F and N) have higher boiling points than expected.

Answer 11

Contain hydrogen bonds which are the strongest intermolecular force and require the most energy to over come

Question 12

Temporary (induced) force

Answer 12

• weakest force
• temporary uneven electron distribution in one molecule
• induces a dipole in neighbouring molecule
• causes weak electrostatic between them
• ## low melting and boiling as little energy is needed to break intermolecular forces

Question 13

What increases the strength of induced forces

Answer 13

• increases surface area of molecule
• increases with larger atoms with grater electron density (electrons)
  (e.g chlorine has more electrons than fluorine so higher electron density)

Question 14

permanent dipole-dipole

Answer 14

• second strongest intermolecular force
• only acts on polar molecules
• arises from a difference in electronegativity between two atoms bonded
• the greater the difference between the two atoms, greater the strength of permanent dipole

Question 15

hydrogen bond

Answer 15

• strongest intermolecular force
• ## only occurs with N-H, O-H, F-H

Question 16

In period 3, P4, S6 , Cl2 rank them from highest to lowest boiling points and explain in terms of intermolecular forces

Answer 16

• all 3 molecules are non- polar molecules
• They only experience the temporary dipole-dipole intermolecular forve
• The sulphur has the largest surface area so will experience strongest intermolecular force
• This means sulphurs boiling point will be the highest as more energy is needed to break the intermolecular forces apart
• The chlorine molecule has the smallest surface area and weakest intermolecular forces, so lowest boiling point

Question 17

HF, HCl, O2 , CH4, rank them from highest to lowest boiling points and explain why in terms of intermolecular forces

Answer 17

• O2 and CH4 are non polar molecules, so will only experience temporary dipole-dipole intermolecular force which are the weakest, Little energy is needed to break these forces, therefore having the lowest boiling points
• CH4 has a larger surface area so will have stronger temporary dipole-dipole so will have a slightly stronger boiling point that O2
• HCL is a polar molecule because of the large difference in electrongeativity between H and Cl. Hal experiences both termporary and permenant dipole , meaning higher boiling point.
• HF experiences hydrogen bonds, as well as 2 other intermolecular forces. this is the strongest intermolecular forces, so large amount of energy is needed to separate molecular apart. Meaning HF has the highest boiling point