18. Periodic Table
General Trends
Elements in the same group:
Group I - Alkali metals
Physical properties:
Chemical properties:
Group VII - Halogens
Physical properties:
Chemical properties:
Group 0 - Noble gases
Physical properties:
Transition Elements
- Elements are arranged in order of their proton numbers in the periodic table increasing from left to right.
- A horizontal row is known as a Period while vertical columns are called Groups.
- Elements of the same group have the same number of valence electrons.
- Elements in the same period have the same number of electron shells.
- Elements become less metallic in nature as they move from left to right across a period in the Periodic Table.
Elements in the same group:
- form ions with similar formulae
- form compounds with similar chemical formulae
- have similar chemical properties
- show trends in their physical and chemical properties
Group I - Alkali metals
Physical properties:
- Soft
- Low density
- Low melting point which decreases down the group
Chemical properties:
- Reactivity increases down the group.
- The ability to lose 1 valence electron increases as the number of electron shells increases down the group. This is due to the decrease in the electrostatic attraction between the outermost shell and the nucleus as the number of shells increases.
Alkali metals react vigorously with water to give hydrogen gas and an alkali. These reactions are strongly exothermic.
Group VII - Halogens
Physical properties:
- Colour intensity of the halogens increases down the group.
- Melting and boiling points increase due to stronger intermolecular attractions between the molecules.
Chemical properties:
- Reactivity decreases down the group as atomic radius increases, since there is decreasing attraction between the nucleus and the electrons in the outermost shell.
- Displacement reaction: A more reactive halogen is able to displace a less reactive halogen from an aqueous solution containing its ions.
Group 0 - Noble gases
Physical properties:
- Collection of monatomic elements that are chemically unreactive.
- They are inert as they already posses the stable duplet (for Helium only) and octet electronic structure.
- Helium is used to fill airships and weather balloons.
- Neon is used to fill light tubes used in colourful advertisement signboards.
- Argon is used to fill light bulbs because it will not react with the hot tungsten filament.
Transition Elements
- Have high densities
- Have high melting points and boiling points
- Have variable oxidation states
- Form coloured compounds
- Are used as catalyst e.g. iron in Haber Process
