1. Describe the change from metallic to non-metallic character across a period.

Across a period, the melting and boiling points of elements increase up until group IV and then it decreases from group V to group 0 it decreases. This is because the elements on the left are metals and element on the right are non-metals (and metals have higher melting and boiling points than non-metals). Keeping this in mind, we can say basic oxides are on the right and acidic oxides occur on the left (since basic oxides are metal oxides and acidic oxides are non-metal oxides!).
In the periodic table above, the elements in purple, blue, yellow and pale green are metals. All the rest are non-metals.

  1. Describe the relationship between Group number, number of outer-shell (valency) electrons and metallic /non-metallic character.

The atoms of elements in the same group have the same number of electrons in their outer shells i.e. the same no. of valence electrons and thus the same valency. Look at the group I:
‘Li’ (Lithium) has an electronic configuration of 2,1
‘Na’ (Sodium) has an electronic configuration of 2,8,1
‘K’ (Potassium) has an electronic configuration of 2,8,8,1.
The valence electrons are all 1 and the valencies are all 1+ in group I


Valency 1 2 3 4 3 2 1


(Note that group III is the group that has the elements ‘B’, ‘Al’, ‘Ga’ etc. Group IV is the column to the right of it and so on. The block of elements in yellow are not considered here as groups).

Down group I, elements become more reactive
Down group VII, element become less reactive.
Down many groups, the elements go from non-metal to metal. (group IV for example, where carbon on the top is a non-metal but lead and tin at the bottom are metals).


Notes submitted by Lintha

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2 thoughts on “C9.1 – Periodic Trends

  1. I have found a mistake.
    It is said that Helium (He) is in Group 1 and has the electronic configuration 1. But, Helium is an element in Group VIII (Noble gases) and it has the electronic configuration 2.


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