3. Periodicity

Question 1

Define ‘degenerate’.

Answer 1

Orbitals in the same subshell with the same energy.

Question 2

Why does the 4s subshell fill and empty first?

Answer 2

• Fills first as it is closer to the nucleus when empty.
• Empties first, as when full, it expands and is further from the nucleus.

Question 3

What is the trend in successive relative ionisation energy of an element? Why?

Answer 3

• There is a general increase.
• Removing an electron from an increasingly positive ion requires more energy.
• The radius decreases because there is less shielding

Question 4

Define ‘first ionisation energy’.

Answer 4

The energy required to remove one mole of electrons from one mole of gaseous atoms to form one mole of gaseous 1+ ions.

Question 5

What three factors does ionisation energy depend on?

Answer 5

• Atomic radius
• Nuclear charge
• Shielding

Question 6

Why does first ionisation energy decrease as you go down a group?

Answer 6

• More shells.
• Greater shielding.
• Increasing atomic radius.
• Increasing nuclear charge.

Question 7

Why is there a general increase in first ionisation energy as you go across a period?

Answer 7

• Same number of shells.
• Similar shielding.
• Decreasing atomic radius.
• Increasing nuclear charge.

Question 8

Why is there a large decrease in first ionisation energy as you go from one period to the next?

Answer 8

• Additional shell.
• Further from nucleus.
• Force of attraction decreases.

Question 9

Define ‘electronegativity’.

Answer 9

The ability of a bonded atom to attract the pair of electrons in a covalent bond.

Question 10

What two factors does electronegativity depend on?

Answer 10

• Nuclear charge.
• Distance between nucleus and electron pair.

Question 11

Why do group 8 have no electronegativity values?

Answer 11

They do not form covalent bonds.

Question 12

Why does electronegativity increase as you go across the period?

Answer 12

There is greater nuclear charge.

Question 13

Why does electronegativity decrease as you go down a group?

Answer 13

The atomic radius increases, meaning the nucleus is further away from the electrons and the force of attraction is weaker.

Question 14

What is the trend in reactivity of group 1? Why?

Answer 14

• As you go down group 1, reactivity increases, as it is easier to lose an electron:
• Increasing electron shells and shielding
• Atomic radius increases.
• Valence electron further from nucleus.
• Attraction between valence electron and nucleus decreases

Question 15

Define ‘electron affinity’.

Answer 15

The energy released when an additional electron is attached to a neutral atom or molecule.

Question 16

Which is the only group to have an electron affinity trend? What is this trend?

Answer 16

• Group 1
• As you go down the group, the electron affinity decreases due to increased shielding.

Question 17

Why does electron affinity increase as you go across a period?

Answer 17

Increasing nuclear charge.

Question 18

What type of oxide do metals form?

Answer 18

Soluble alkaline oxide

Question 19

What type of oxide do non-metals form?

Answer 19

Soluble, acidic oxides

Question 20

Define ‘amphoteric’.

Answer 20

An element or compound that can act both as an acid and a base.

Question 21

Which oxide is amphoteric?

Answer 21

Aluminium oxide

Question 22

Is pure water alkaline, acidic or neutral at 298K

Answer 22

Neutral

Question 23

What is the normal pH of rainwater? Why?

Answer 23

• pH 5.6
• Carbon dioxide dissolves in the water to form carbonic acid.

Question 24

What naturally produces sulfur dioxides and nitrogen oxides?

Answer 24

Volcanoes and decomposing vegetation.

Question 25

Why is the acidification of sea water negative?

Answer 25

Affects the ability of coral reefs and shellfish to calcify their skeletons.