Period 3 elements

Explanation for the melting & boiling points and conductivity of the period 3 elements.

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Period 3 elements
Melting and boiling points
Na Mg Al Si P S Cl Ar
Melting 371 922 933 1683 317 392 172 84
point (K)
Boiling 1156 1380 2740 2628 553 718 238 87
point (K)
Cooler Hottest Cooler
The differences in melting and boiling points across Period elements are down to their structures.
Giant structures (in the middle) have stronger bonding than molecular or atomic structures (on the
left and right).
The three metals with giant metallic structures (Na, Mg and Al) have increasing melting and boiling
points because they have a greater number of protons, so more electrons hold the lattices together.
Silicon is a giant covalent structure and also has high melting and boiling points.
The non-metals, (P, S, Cl, Ar), mostly decrease down the period as there are more electrons in each
atom, meaning they cannot pack tightly together, which decrease the size of the van der Waals
Na Mg Al Si P S Cl Ar
Relative 0.26 0.42 1 0.1 0 0 0 0
(Al = 1)
Weaker Greatest Weaker
The elements to the left of the period (Na, Mg and Al) are all metals so can conduct electricity well.
This is because they are held together with metallic bonding, where the nucleus of each atom is
attracted to a `sea' of electrons. These electrons are free to move which is how electricity is
conducted. Their electrical conductivity increases from sodium to aluminium because there are an
increased number of electrons free to carry charge.
Silicon is a `metalloid' so has some metallic properties (another example is carbon). Its giant covalent
structure does have a few `delocalised' electrons that can carry charge, especially at higher
temperatures, so it does have a very weak conductivity.
The non-metals of the period (P, S, Cl and Ar) have no electrical conductivity because their electrons
are not delocalised. In P, S and Cl this is because they are held by strong covalent bonds. In argon
this is because its outer shell or energy level is full, which holds the electrons strongly.


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