S-Cool Revision Summary

S-Cool Revision Summary

The Periodic Table arranges the elements in order
of proton number. Hydrogen has a proton number of 1 so heads the table, followed
by helium with proton number 2.

Elements whose atoms have 1 electron in their outer shell are put into Group
1 of the periodic table. Group 2 elements have 2 electrons in their outer shell
and so on.

The groups are arranged side by side in the periodic
table. These horizontal rows are called periods.

Period 1 elements have their outer electrons in the first energy shell. Period
2 elements have their outer electrons in the second energy shell.

The periodic table has eight groups of elements, plus a block of transition
metals.

Some of the groups have special names:

  • Group 1: Alkaline metals.

  • Group 2: Alkaline earth metals.

  • Group 7: Halogens.

  • Group 0: Noble gases.

The noble gases are colourless, unreactive gases.
As you go down group 0 their density increases.

The halogens have similar properties since they all
have 7 electrons in their outer shell. Reactivity does decrease down the
group
as it becomes more difficult to gain an extra electron.

Halogens exist as molecules.

The alkali metals all have one electron in their outer
shell. They are reactive soft metals.

The alkali metals are reactive with water producing alkaline solutions. Reactivity
increases down the group, as the loss of an electron becomes easier as the size
of the atom increases.

The alkaline earth metals are less reactive than group
1 since they need to lose 2 electrons to gain a full outer shell.

Group 2 reactivity and melting/boiling points increase down the group,
as does group1.

Transition metals and their compounds are often
used in industry as catalysts.