Reactivity Changes Down Groups of the Periodic Table

This is best considered in terms of the attraction between the outer electron and the nucleus.

The outer electron means either the one about to be removed from a metal atom do that it can form a positive ion or the electron about to be added to a non-metal atom so it can form a negative ion. Eg Na (2,8,1) becomes Na+ (2,8,0) and Cl (2,8,7) becomes Cl- (2,8,8)

Think of small atoms (near the top of the Periodic Table).

The attraction is large since the distance is only very small. The metal atom finds it difficult to lose the electron. The non-metal atom finds it very useful to gain an electron because it can be held very tightly. So, metals near the top of the Periodic Table are fairly unreactive and the non-metals near the top of the Periodic Table are very reactive.

Think of large atoms (near the bottom of the Periodic Table).

The attraction is small since the distance is quite large. The metal atom finds it easy to lose the electron. The non-metal atom finds it of little use to gain an electron because it can be held only fairly weakly. So, metals near the bottom of the Periodic Table are quite reactive and the non-metals near the bottom of the Periodic Table are fairly unreactive.

So, in terms of trends,

Metals become more reactive as you go down the group.

eg Lithium .. Sodium .. Potassium .. Rubidium .. Caesium

Try to quote evidence (Li and Na don’t usually catch fire in water,
Cs reacts explosively with water….ask your teacher to show the video!)

Non-metals become less reactive as you go down the group.

eg Fluorine .. Chlorine .. Bromine .. Iodine

Try to quote evidence
(you can do displacement reactions with these elements….
ask your teacher to show the video of what fluorine can do!)

Water Experiment (courtesy of Sky Learning www.skylearning.co.uk)

The students are shown what happens when different metals are reacted with water. This experiment is shown in classrooms up and down the country but never on such a large scale as this!. Note the trend as you go from Li to Na to K. All three of these elements have 1 electron in their outer shell (so they're in the Group 1 of the Periodic Table) but they get more much reactive as they get bigger.

Watch the Water experiment below