Peridoic Table

Period 1 Period 2 Period 3 Period 4 Period 5 Period 6 Period 7

Groups There are 8 groups: Gp I, II, III, IV, V, VI, VII, 0 Group no. = number of outermost shell electrons Group I : alkali metals Group II: alkaline earth metals Group VII: halogens Group 0: noble gases

Groups For noble gases (group 0), they have either duplet structure (He has 2 outermost shell electrons) or octet structure (Ne and Ar have 8 outermost shell electrons) which are very stable structures. The outermost electron shell of noble gases are fully occupied (duplet or octet), they are chemically unreactive, so their chemical properties are equivalent to atoms with 0 outermost shell electrons. As a result, they are called group 0 elements.

Group I: Li, Na, K Group I elements are metals, their chemical properties are similar because they have same number of outermost shell electrons. Their physical properties are gradually change (different). E.g. reaction with water Sodium reacts readily with water. It melts in water to form a silvery ball and burns with a golden yellow flame. Potassium reacts vigorously with water. It melts in water to form a silvery ball and burns with a lilac flame. The reactivity increases down the group.

Group I: Li, Na, K Hydrogen has 1 outermost shell electron. Does it belong to group I ? No. It is because group I elements are metals. Hydrogen is a non-metal.

Group VII: F, Cl, Br, I Group VII elements are non-metals, their chemical properties are similar because they have same number of outermost shell electrons. Their physical properties are gradually change (different). E.g. reaction with colourless sodium hydrogensulphite solution Greenish yellow chlorine gas changes to colourless. Reddish brown bromine liquid changes to colourless. The reactivity decreases down the group.

Periods There are 7 periods: period 1 to 7 Period 1: only H and He Period 2: Li, Be, B, C, N, O, F, Ne Period 3: Na, Mg, Al, Si, P, S, Cl, Ar Period no. = number of electron shell occupied by electrons Across a period, elements change from metals to semi-metals (metalloids) and then non-metals.

Metals Most elements are metals. Mercury: the only liquid metal at room temperature and pressure Metals are usually shiny, hard, malleable, ductile and with high melting points and boiling points.

Semi-metals In the first 20 elements, only B and Si are semi-metals. Silicon is used in the manufacture of computer chips.

Non-metals There are less than 20 non-metal elements. Solid: C, P, S, I Liquid: Br (the only liquid non-metal) Gas: H, He, N, O, F, Ne, Cl, Ar Non-metals usually have low melting points and boiling points (except carbon).