Chapter 8 (Periodicity)

Question 1

Define Periodicity

Answer 1

The repeating pattern of physical or chemical properties going across the periods.

Question 2

Explain the change in the atomic radius across a period?

Answer 2

Decreases from left to right, because there are more protons which create a more positive charge attraction for electrons which are in the same shell with similar sheilding.

Question 3

Explain the change in the atomic radius down a group?

Answer 3

Increases as there is an additional outer shell of electrons.

Question 4

Explain the change in first ionisation energy across a group?

Answer 4

Increases as there is an increasing number of protons so a greater positive attraction so more energy required to remove electrons.

Question 5

Explain the change in the first ionisation energy down a group?

Answer 5

Decreases as there is an additional outer shell and more shielding between the outer shell and the nucleus so less energy required to remove an electron.

Question 6

Why is there a decrease in first ionisation energy between Mg and Al?

Answer 6

Mg has its outer shell in a 3s sub-shell whereas Al is starting to fill the 3p sub-shell. Al electron is easier to remove as 3p electrons are higher in energy.

Question 7

Why is there a decrease in first ionisation energy between P and S?

Answer 7

S outer electron is being paired up with another electron in the same 3p orbital. When the 2nd electron is added then there is a slight repulsion between two negatively charged electrons which makes it easier to remove.

Question 8

Explain the melting and boiling points of Na, Mg and Al

Answer 8

They have strong metallic bonding which gets stronger the more electrons are added as then more electrons are released from the outer shell into the sea of electrons. A smaller sized ion with a greater positive charge also makes the bonds stronger so more energy is needed to break the bonds.

Question 9

Explain the melting point of Si

Answer 9

It is macromolecular so there are many strong covalent bonds between atoms, high amounts of energy is needed to break covalent bonds.

Question 10

Explain the melting point of Cl2, S8 and P4

Answer 10

They are simple molecular so have weak Van der Waals between molecules so little energy is needed to break them.

S8 has a higher mp than P4 because it has more electrons and larger surface area so stronger Van der Waals between molecules.

Question 11

Explain the melting point of Ar

Answer 11

Ar is monatomic so has weak Van der Waals between atoms.

Question 12

Define first ionisation energy?

Answer 12

The energy required to remove an electron from a gaseous atom.