Chemistry

Periodic Table

*Groups
-vertical columns
-group number represents the number of outermost shell electrons in its atom
-under the same group, the elements have similar chemical properties

*Periods
-horizontal rows
-under the same period, elements have the same number of occupied electron shell

**Group I ---Alkali Metals
Similarities of Group I elements
-have relatively(较） low melting and boiling points when compared with Group II,III and transition metals
-soft and can be cut with a knife
-low densities, can float on water
-reactive metals and must be stored in paraffin oil to prevent them from reacting with air
-react vigorously with water to give hydrogen gas and also alkaline solution
-react with non-metals to form compounds called salts
Differences in reactivity of Group I elements
Group I metals are all very reactive. The reactivity of Group I elements increase as moving down the group.

Group II ---Alkaline earth metals
Similarities of Group II elements
-have relatively loe melting and boiling points when compared with other metals
-low densities
-reactive metals and react readily with dilute hydrochloric acid to give hydrogen gas
-react with non-metals to form compounds called salts
Differences in reactivity of Group II elements
Group II elements are less reactive than Group I elements. The reactivity of Group II elements increase as moving down the group.

Group VII ---Halogen
Similarities in properties of Group VII elements
-poisonous and smelly
-non-metals
-react with metals to form compounds called salts
Difference in the reactivity of Group VII elements
The reactivity of these elements decrease as moving down the group.

Group O/VIII --- Noble gas
Similarities in properties of Group O elements
-colourless gas
-low melting and boiling points
-very unreactive (stable)

Stability of Group O elements
*octet rule---atoms become stable by having eight electrons in their outermost shells