Trends within the Periodic Table
Group 1
The elements in Group 1 of the Periodic Table are known as the alkali metals. They have some characteristics in common:
They are low-density metals (the first three elements in Group 1 are less dense than water)
They react with non-metals to form ionic compounds in which the metal ion has a charge of +1. The compounds are white solids that dissolve in water to form colourless solutions
They react with water to release hydrogen
They form hydroxides that dissolve in water to make alkaline solutions.
In Group 1, the further down the group an element is:
The more reactive it is
The lower its melting point and boiling point.
Transition Elements
Compared with the elements in Group 1, the transition elements:
Have higher melting points (except for mercury, which is a liquid at room temperature) and higher densities
Are stronger and harder
Are much less reactive, so do not react as vigorously with water or oxygen
Many transition elements also:
Have ions with different charges
Form coloured compounds
Are useful as catalysts
Group 7
The elements in Group 7 of the Periodic Table are known as the halogens. The have some characteristics in common:
They react with metals to form ionic compounds in which the halide ion carries a charge of --1.
In Group 7, the further down the group an element is:
The less reactive it is
The higher its melting point and boiling point
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 are due to the activity of electrons in the outer shells (highest energy levels). The higher the energy level of the outer electrons:
The more easy it is for electrons to be lost
The more difficult it is for electrons to be gained