The elements in Group 1 of the periodic table (known as the alkali metals):
- are metals with low density (the first three elements in the group are less dense than water)
- react with non-metals to form ionic compounds in which the metal ion carries a charge of +1.
The compounds are white solids that dissolve in water to form colourless solutions
- react with water, releasing hydrogen
- form hydroxides that dissolve in water to give alkaline solutions.
In Group 1, the further down the group an element is, the more reactive the element.
Compared with the elements in Group 1, transition elements:
- have higher melting points (except for mercury) and higher densities
- are stronger and harder
- are much less reactive and so do not react as vigorously with water or oxygen.
Many transition elements have ions with different charges, form coloured compounds and are useful as catalysts.
e) The elements in Group 7 of the periodic table (known as the halogens) react with metals to form
ionic compounds in which the halide ion carries a charge of –1.
f) In Group 7, the further down the group an element is:
- the less reactive the element
- the higher its melting point and boiling point.
g) A more reactive halogen can displace a less reactive halogen from an aqueous solution of its salt.
The trends in reactivity within groups in the periodic table can be explained because the higher the
energy level of the outer electrons:
- the more easily electrons are lost
- the less easily electrons are gained.