Lesson test: Chemical bonding

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Chemical bonding

1.[2p]
What determines whether two atoms bond?

Whether the bonded arrangement has lower total energy than the separated atoms

Correct

Whether both can reach a full octet

The answer is: Whether the bonded arrangement has lower total energy than the separated atoms

Whether their electronegativities differ

The answer is: Whether the bonded arrangement has lower total energy than the separated atoms

Whether one has a vacant orbital

The answer is: Whether the bonded arrangement has lower total energy than the separated atoms

2.[2p]
For sodium chloride the steps are sublimation +107, ionisation +496, dissociation +122, electron affinity -349 and lattice energy -787 kJ per mol. What is the enthalpy of formation?

CorrectNot quite: -411

3.[2p]
In the Born-Haber cycle for NaCl, the steps producing the gaseous ions cost 725 kJ per mol in total. What pays for them?

The lattice energy released when the ions assemble into the crystal

Correct

The electron affinity of chlorine

The answer is: The lattice energy released when the ions assemble into the crystal

The ionisation energy of sodium

The answer is: The lattice energy released when the ions assemble into the crystal

The entropy of the reaction

The answer is: The lattice energy released when the ions assemble into the crystal

4.[2p]
Why is an ionic crystal hard but brittle?

Shearing brings like charges into contact, so the lattice repels itself apart along the plane

Correct

The ions are held by weak forces that break easily

The answer is: Shearing brings like charges into contact, so the lattice repels itself apart along the plane

The crystal contains microscopic cracks

The answer is: Shearing brings like charges into contact, so the lattice repels itself apart along the plane

Ionic bonds are directional and snap when bent

The answer is: Shearing brings like charges into contact, so the lattice repels itself apart along the plane

5.[2p]
Why does the bond angle fall from 109.5 degrees in methane to 104.5 in water?

Lone pairs are held by one nucleus only, so they spread wider and compress the bonding pairs

Correct

Oxygen is smaller than carbon

The answer is: Lone pairs are held by one nucleus only, so they spread wider and compress the bonding pairs

Water has fewer electrons in total

The answer is: Lone pairs are held by one nucleus only, so they spread wider and compress the bonding pairs

The O-H bond is more polar than C-H

The answer is: Lone pairs are held by one nucleus only, so they spread wider and compress the bonding pairs

6.[2p]
Molecular orbital theory succeeds where Lewis structures fail most visibly. What is the case?

$O_{2}$ has two unpaired electrons and is paramagnetic

Correct

$H_{2}$ has a single bond

The answer is: $O_{2}$ has two unpaired electrons and is paramagnetic

$N_{2}$ has a triple bond

The answer is: $O_{2}$ has two unpaired electrons and is paramagnetic

${CO}_{2}$ is linear

The answer is: $O_{2}$ has two unpaired electrons and is paramagnetic

7.[1p]
Using bond order as (bonding electrons minus antibonding electrons) divided by two, what is the bond order of ${He}_{2}$ ?

CorrectNot quite: 0

8.[2p]
Match each property of metals with what explains it.

Electrical conduction
Malleability
Lustre

the cores can slide past each other while the electron sea holds them together
delocalised electrons are already free to move
loose electrons absorb and re-emit light across the visible range

Show the answer

Electrical conduction: delocalised electrons are already free to move Malleability: the cores can slide past each other while the electron sea holds them together Lustre: loose electrons absorb and re-emit light across the visible range

1.[2p] What determines whether two atoms bond?

2.[2p] For sodium chloride the steps are sublimation +107, ionisation +496, dissociation +122, electron affinity -349 and lattice energy -787 kJ per mol. What is the enthalpy of formation?

3.[2p] In the Born-Haber cycle for NaCl, the steps producing the gaseous ions cost 725 kJ per mol in total. What pays for them?

4.[2p] Why is an ionic crystal hard but brittle?

5.[2p] Why does the bond angle fall from 109.5 degrees in methane to 104.5 in water?

6.[2p] Molecular orbital theory succeeds where Lewis structures fail most visibly. What is the case?

7.[1p] Using bond order as (bonding electrons minus antibonding electrons) divided by two, what is the bond order of He2?

8.[2p] Match each property of metals with what explains it.

1.[2p]
What determines whether two atoms bond?

2.[2p]
For sodium chloride the steps are sublimation +107, ionisation +496, dissociation +122, electron affinity -349 and lattice energy -787 kJ per mol. What is the enthalpy of formation?

3.[2p]
In the Born-Haber cycle for NaCl, the steps producing the gaseous ions cost 725 kJ per mol in total. What pays for them?

4.[2p]
Why is an ionic crystal hard but brittle?

5.[2p]
Why does the bond angle fall from 109.5 degrees in methane to 104.5 in water?

6.[2p]
Molecular orbital theory succeeds where Lewis structures fail most visibly. What is the case?

7.[1p]
Using bond order as (bonding electrons minus antibonding electrons) divided by two, what is the bond order of ${He}_{2}$ ?

8.[2p]
Match each property of metals with what explains it.