Live Class - AS CHEM - 3rd Period of Periodic Table - Period 3 Elements - Periodic Table - Elements

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In this lecture we go over the trends followed by period 3 elements, including their melting points and electrical conductivities. Their reactions with water, their oxides' reactions with water, and oxidation states are also discussed.

Melting and boiling points rise across the three metals because of the increasing strength of the metallic bonds.

The number of electrons which each atom can contribute to the delocalised "sea of electrons" increases. The atoms also get smaller and have more protons as you go from sodium to magnesium to aluminium.
Live Class - AS CHEM - Periods in Periodic Table - Period 3 - Trends of Properties Across Periods3rd Period
Phosphorus, sulphur, chlorine and argon are simple molecular substances with only van der Waals attractions between the molecules. Their melting or boiling points will be lower than those of the first four members of the period which have giant structures.

The sizes of the melting and boiling points are governed entirely by the sizes of the molecules.

Phosphorus
Phosphorus contains P4 molecules. To melt phosphorus you don't have to break any covalent bonds - just the much weaker van der Waals forces between the molecules.

Sulphur
Sulphur consists of S8 rings of atoms. The molecules are bigger than phosphorus molecules, and so the van der Waals attractions will be stronger, leading to a higher melting and boiling point.

Chlorine
Chlorine, Cl2, is a much smaller molecule with comparatively weak van der Waals attractions, and so chlorine will have a lower melting and boiling point than sulphur or phosphorus.

Argon
Argon molecules are just single argon atoms, Ar. The scope for van der Waals attractions between these is very limited and so the melting and boiling points of argon are lower again.

Electrical Conductivites
Sodium, magnesium and aluminium are all metals. They have metallic bonding, in which the nuclei of metal atoms are attracted to delocalised electrons.

Going from sodium to aluminium, the number of delocalised electrons increases, there are more electrons that can move and carry charge, through the structure, the electrical conductivity increases. Silicon can be deemed as a semi conductor due to the nature of its structure. Elements to the right of Silicon do not conduct electricity.


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