1.4 Periodicity

Question 0

Explain the trend in atomic radius across period 3

Answer 0

The nuclear charge increases across the period while the number of electron shells remains the same. So the electrostatic force of attraction between the outer electron and the nucleus increases, so the outer electrons are pulled closer causing the atomic size to decrease.

Question 1

Describe the trend in atomic radius across period 3

Answer 1

The atomic radius DECREASES across group 3

Question 2

Describe the trend in ionisation energy across period 3

Answer 2

The general trend is an INCREASE across period 3. However there is a decrease between groups 2-3 (Mg to Al) and between groups 5-6 (P to S)

Question 3

Explain why there is a decrease in ionisation energy between groups 2-3 (Mg to Al)

Answer 3

Because Mg has a 3s orbital while Al has a 3p orbital. An a 3p orbital is in a higher energy level. Therefore less energy is required to overcome the forces of attraction and remove an electron.

Question 4

Explain the GENERAL trend of ionisation energy across period 3

Answer 4

The ionisation energy increases across period 3 is because the nuclear charge increases while the number of electron shells reminds the same. So the forces of attraction between the nucleus and the outer electrons are greater, making it harder to remove an electron.

Question 5

Describe the trend in electronegativity across period 3

Answer 5

Electronegativity INCREASES across period 3

Question 6

Explain why there is a decrease in ionisation energy between groups 5-6 (P to S)

Answer 6

Sulphur has a pair of electrons in its outer shell, whereas Phosphorous only has one. The pair of electrons in Sulphur’s outer shell are already repelling each other, so less energy is required to remove an electron.

Question 7

Explain the trend in electronegativity across period 3

Answer 7

Across period 3 the nuclear charge of the atoms increases while the number of electron shells remains the same. Therefore the electrons are attracted more strongly across the period.

Question 8

Describe the trend in melting point from Na to Al and explain it.

Answer 8

The melting point increases. This is because as you move across the group there more electrons in the sea of delocalised electrons, so they are held together more securely in a giant metallic lattice. Requiring more energy to overcome the electrostatic forces of attraction.

Question 9

Explain why silicon has the highest melting point of all the elements in period 3

Answer 9

Because it forms a giant covalent structure

Question 10

What determines the melting point of the non-metals with molecular structures in period 3 (phosphorus-chlorine)

Answer 10

The strength of the van der waals forces between the molecules and how closely they can pack together

Question 11

Put phosphorous, sulphur and chlorine in order from highest melting point to lowest melting point.

Answer 11

Highest melting point: sulphur (S8)
Then phosphorous (P4)
Lowest melting point: chlorine (Cl2)