7 Periodicity

Question 1

What does periodicity mean?

Answer 1

A repeating trend in properties of the elements across each period of the periodic table.

Question 2

What are groups?

Answer 2

A vertical column in the periodic table.

Question 3

What are periods?

Answer 3

A horizontal row of elements in the periodic table.

Question 4

What is the first ionisation energy?

Answer 4

The first ionisation energy is the energy needed to remove 1 mole of electrons from 1 mole of gaseous atoms.
E.g Na-> Na+ + e-

Question 5

What factors affect ionisation energy?

Answer 5

1) Atomic radius
2) Nuclear charge
3) Electron shielding

Question 6

How does atomic radius affect ionisation energy?

Answer 6

• The greater the distance between the nucleus and the outer electrons, the less the nuclear attraction.
• The force of attraction falls off sharply with increasing distance, so atomic radius has a large effect.

Question 7

How does nuclear charge affect ionisation energy?

Answer 7

• The more protons there are in the nucleus of an atom, the greater the attraction between the nucleus and the other outer electrons.

Question 8

How does electron shielding affect ionisation energy?

Answer 8

• Electrons are negatively charged and so inner-shell electrons repel outer-shell electrons.
• This repulsion, called the shielding effect, reduces the attraction between the nucleus and the outer electrons.

Question 9

What is the second ionisation energy?

Answer 9

The energy required to remove one electron from each ion in one mole of gaseous 1+ ions of an element to form one mole of gaseous 2+ ions.
He+ -> He2+ + e-

Question 10

Successive ionisation energies:

Answer 10

• The number of electrons in the outer shell
• The group of the element in the periodic table
• The identity of an element

Question 11

What is the trend in first ionisation energy down a group?

Answer 11

• First ionisation energy decreases down a group.

E.g He, Ne, Ar

Question 12

Why does first ionisation energy decrease down a group?

Answer 12

• Elements further down a group have extra electron shells compared to ones above.
• The extra shells mean that the atomic radius increases so outer electrons are further away from the nucleus, which reduces their nuclear attraction.
• The extra inner shells cause an increase in shielding.

Question 13

What is the trend in first ionisation energy across a period?

Answer 13

• First ionisaton energy increases across a period.

E.g Li, Be, B, C, N, O, F, Ne

Question 14

Why does first ionisation energy increase across a period?

Answer 14

• The number of protons increases, so the nuclear charge increases.
• The extra electrons are added to the outer energy level, so shielding is similar and does not really have an effect.
• This pulls the electrons closer to the nucleus, decreasing atomic radius and increasing nuclear attraction.

Question 15

Why is there a fall in first ionisation energy from beryillium to boron?

Answer 15

• It marks the start of filling the 2p sub-shell.
• The 2p sub-shell in boron has a higher energy than the 2s sub-shell in beryllium.
• Therefore in boron the 2p electron is easier to remove than one of the 2s electrons in beryllium.
• The first ionisation energy of boron is less than the first ionisation energy of beryilium.

Question 16

Why is there a fall in first ionisation energy from nitrogen to oxygen?

Answer 16

• It marks the start of electron pairing in the p-orbitals from the 2p sub-shell.
• In oxygen, the paired electrons in one of the 2p orbitals repel one another, making it easier to remove an electron from an oxygen atom than a nitrogen atom.
• Therefore the first ionisation energy of oxygen is less than the first ionisation energy of nitrogen.

Question 17

What is metallic bonding?

Answer 17

The electrostatic attraction between positive metal ions (cations) and delocalised electrons.

Question 18

What are properties of metals?

Answer 18

• Strong metallic bonds
• High electrical conductivity
• High melting and boiling points

Question 19

What is a giant covalent lattice?

Answer 19

A 3D structure of atoms, bonded together by strong covalent bonds.

Question 20

What are the properties of a giant covalent lattice?

Answer 20

• High melting and boiling points
• Insoluble
• Non-conductors of electricity

Question 21

What does a high ionisation energy mean?

Answer 21

There’s a strong attraction between the electron and the nucleus, so more energy is needed to overcome the attraction and remove the electron.