Atomic theory 10

Question 1

Use electronegativity values to predict the type of bond expected between hydrogen and sulfur. (L.C)

Answer 1

Weakly polar / almost non-polar

Question 2

Write the chemical equation for hydrogen sulphide. (L.C)

Answer 2

H₂S

Question 3

Would you expect the hydrogen sulphide molecule to be linear or non-linear in shape? Justify your answer.(L.C)

Answer 3

• Non-linear

- There are lone(non-bonding) pairs

Question 4

Hydrogen sulphide has a boiling point of 212.3 K and water has a boiling point of 373 K. Account for the difference in the boiling points of these substances. (L.C)

Answer 4

• Water has hydrogen bonds
• Weak dipole-dipole forces in H₂S /
• Weaker intermolecular forces in H₂S

Question 5

Would you expect hydrogen sulphide to be soluble in water? Explain your answer. (L.C)

Answer 5

• No / only slightly soluble

- Does not form hydrogen with water

Question 6

Explain the term intermolecular forces (L.C)

Answer 6

Attractive (repulsive) forces between molecules.

Question 7

Use your knowledge of intermolecular forces to explain why methane has a very low boiling point (164°C) (L.C)

Answer 7

• Very weak intermolecular forces

- Weak Van der Waal’s forces of attraction

Question 8

The relative molecular mass of methane is only slightly lower than that of water but the boiling point of water is much higher (100°C). Suggest a reason for this. (L.C)

Answer 8

• Much stronger hydrogen bonds between water molecules

Question 9

Why do ionic substances conduct electricity when molten or dissolved in water but not in the solid state? (L.C)

Answer 9

Molten/dissolved : ions free to move

Solid : ions not free to move / ions locked in position

Question 10

Show that the ammonia molecule (NH₃) has polar covalent bonding. Describe the processes involved when ammonia dissolves in water. (L.C)

Answer 10

• There is an electronegativity difference between N and H

- Showing unequal sharing

Question 11

Define electronegativity (L.C)

Answer 11

The relative power of attraction an atom of an element has for the shared pair of electrons in a covalent bond.

Question 12

Account for the difference in bond angle between the two molecules, 107.3 degrees in ammonia and 109.5 degrees in silane. (L.C)

Answer 12

• Lone pair of electrons has greater repelling power than a bond pair of electrons.
• Bonds in NH₃ pushed closer together than in SiH₄
• Ammonia has three bond pairs where silane has four bond pairs

Question 13

Use electronegativity values to determine which bond, the N-H bond in ammonia or the Si-H bond in silane, is the more polar. (L.C)

Answer 13

N - H = 0.84
Si - H = 0.3
⇒
N - H is more polar

Question 14

Define electronegativity (L.C)

Answer 14

The relative power of attraction an atom of an element has for the shared pair of electrons in a covalent bond.

Question 15

Use electronegativity values to determine which bond, the N-H bond in ammonia or the Si-H bond in silane, is the more polar. (L.C)

Answer 15

N - H = 0.84
Si - H = 0.3
⇒ N - H is more polar

Question 16

Which of the two substances ammonia (NH₃) or silane (SiH₄) has hydrogen bonding between its molecules? Justify your answer. (L.C)

Answer 16

• Ammonia

- In ammonia hydrogen bonded to a small highly electronegative element

Question 17

Give the reason why a molecule with polar bonds can be non-polar. (L.C)

Answer 17

• Centres of positive and negative charge coincides

- Dipole moments cancel

Question 18

Why is there an increase in electronegativity value moving from gallium to germanium in the periodic table? (L.C)

Answer 18

• Nuclear charge increasing

- Atomic radius increasing

Question 19

Define electronegativity (L.C)

Answer 19

The relative power of attraction an atom of an element has for the shared pair of electrons in a covalent bond..

Question 20

Write the molecular formula for the simplest compound formed between germanium (IV) and hydrogen. (L.C)

Answer 20

GeH₄

Question 21

Would you expect the compound GeH₄ to be water soluble? Explain your answer. (L.C)

Answer 21

• No

- GeH₄ is a non-polar solute

Question 22

Suggest a reason why ammonia has the highest boiling point of ammonia, phosphine and arsine. (L.C)

Answer 22

Hydrogen bonding in ammonia (azane) is stronger than the other intermolecular forces in phosphane or arsane.

Question 23

Suggest a reason why phosphine’s boiling point is lower than that of arsine. (L.C)

Answer 23

• Phosphine molecules are smaller

- Phosphine has a smaller degree of intermolecular forces

Question 24

Define electronegativity (L.C)

Answer 24

The relative power of attraction an atom of an element has for the shared pair of electrons in a covalent bond.

Question 25

Use electronegativity values to predict the type of bonding in chlorine monofluoride. (L.C)

Answer 25

Polar covalent

Question 26

Define electronegativity (L.C)

Answer 26

The relative power of attraction an atom of an element has for the shared pair of electrons in a covalent bond.,