Physical properties of period 3 elements

Which of the period 3 substances form giant covalent lattices?

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Which of the following period 3 substances form covalent bonds between their atoms?

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Phosphorus

Sulphur

Chlorine

Which trends are generally the case for all periods? (3)

Atomic radius decreases across each period.

First ionisation energy increases across each period

There is no clear upwards or downwards trend in melting point across a period

Magnesium is smaller than sodium because

there are more protons attracting the electrons towards the nucleus

Ionisation energy decreases between…

magnesium and aluminium

phosphorus and sulfur.

The explanation for the dip between phosphorus and sulfur is that, as we move from Group 5 to Group 6, there is some repulsion between electrons which are…

paired or in the same orbital

Across a period, the general trend is for first ionisation energy to…

increase

Across Period 3, shielding...

stays roughly the same

The 1st ionisation energy across Period 3 generally…

increases

Explain why the first ionisation energy of aluminium is less than magnesium.

The outermost electron of aluminium is in a p orbital whilst magnesium's is in an s orbital.

Electrons in the s orbital repel, and shield, the electrons in the p orbital, to some extent.

This means less energy is required to remove the first electron in the p orbital of aluminium.

Therefore, aluminium has a lower first ionisation energy.

Explain why the first ionisation energy of sulphur is less than phosphorus.

Phosphorus has only 1 electron in each of its p orbitals.

Sulphur has 2 electrons in one of its p orbitals, causing increased electron repulsion.

This means less energy is required to remove an electron from sulphur.

Therefore, sulphur has a lower first ionisation energy than phosphorus.

trend in melting point across period 3