7 - Periodicity

Question 1

How is the periodic table structured?

Answer 1

• increasing atomic number
• in periods showing repeating trends in physical and chemical properties (periodicity)
• in groups having similar chemical properties

Question 2

Define 1st ionisation energy

Answer 2

energy needed to remove 1 mol of electrons from 1 mol of gaseous atoms to form 1 mol of gaseous 1+ ions

Question 3

Explain the trend in 1st IE across Periods 2 and 3 & down the groups in terms of:

• attraction / electron shielding
• nuclear charge
• atomic radius

Answer 3

1. Electron shielding - increased shielding reduces the attraction between the nucleus and the outer electrons
2. Nuclear charge - The more protons there are in the nucleus of an atom, the greater the attraction between the nucleus and the outer electrons
3. Atomic radius - The greater the distance between the nucleus and the outer electrons, the less the nuclear attraction. Atomic radius has a large effect

Question 4

What is metallic bonding

Answer 4

A strong electrostatic attraction between cations and delocalised electrons

Question 5

What can you see periodicity / periodic trends in?

Answer 5

• electronic configuration
• ionisation energies
• structure
• melting points

Question 6

Trend in first ionisation energy down a group

Answer 6

First ionisation energy DECREASES down a group.

• Atomic radius increases
• More electrons so shielding increases
• Nuclear charge increases, but outweighed by other factors
• hence Nuclear attraction on outer electrons decreases
• Ionisation energy decreases

Question 7

Trend in first ionisation energy across a period

Answer 7

Across a period, 1st ionisation energy increases.

• Nuclear charge increases
• Same shell so atoms experience similar shielding
• Since nuclear attraction increases, atomic radius decreases
• Hence the first ionisation energy increases

Question 8

Anomalies in first ionisation energy trend across a period

Answer 8

Across period two, the first ionisation energy graph generally increases, but falls in two areas: between beryllium and boron; and between nitrogen and oxygen.

Beryllium & Boron:
The fall marks the start of filling the 2p sub shell in boron. The 2p sub shell in boron has a HIGHER ENERGY than the 2s sub shell in beryllium. Hence, the 2p electron is easier to remove, and the 1st IE of boron is less than that of beryllium

Nitrogen & oxygen:
The fall in 1st IE here marks the start of electron PAIRING in the p orbitals of the 2p sub shell. In nitrogen and oxygen, the highest energy electrons are in a 2p sub shell. In oxygen the pair electrons in one of the 2p orbitals REPEL one another, making it easier to remove an electron from an oxygen atom rather than a nitrogen atom, therefore decrease in the 1st IE of oxygen

Question 9

Physical properties of giant metallic lattices.

• electrical conductivity
• MP & BP
• solubility

Answer 9

A