The table is based on classifying the elements in order of ascending atomic number. (Remember that the atomic number is numerically equal to the number of protons in an atom of the element).
The horizontal rows are called Periods and the vertical columns are called Groups.
Group I contains the Alkali metals, (Group II contains the Alkaline Earth Metals); Group VII contains non-metals known as the Halogens and Group VIII (sometimes called group 0) contains the Noble (or “Inert” or “Rare” ) Gases.
More than three quarters of the elements are metals which are all solids at room temperature and pressure (except mercury, Hg); have high melting points; are shiny (lustrous) when polished; can easily be hammered or bent or stretched into shape (ie. They are malleable and ductile) and are good conductors of heat and electricity. Less than one quarter are non-metals which usually have low melting points and boiling points (actually half are gases); are usually dull; are usually brittle and are poor conductors of heat and electricity (graphite is a good conductor). Metals form ionic compounds with non-metals; non-metals also form covalent compounds with other non-metals.
Metal oxides and metal hydroxides (bases) will neutralise acids to produce salt solutions and water.
Carbon dioxide, sulphur dioxide, nitrogen dioxide react with water to produce solutions of acids.
The maximum number of electrons in the outer shell of an atom is 2, then 8 and then 18 etc., but the third shell appears to have an outer shell of eight electrons because it possesses a sub-shell of ten electrons. Each new period commences when an outer shell is full of electrons.
Elements that have the same number of electrons in their outer shells undergo similar chemical reactions but they vary in vigour! thus the elements are organised in vertical groups where each group member has similar chemical characteristics to others in the group.
As you go down a group, metals become more reactive because their atoms get bigger making it easier for them to lose electrons. The melting points decrease because metallic bonding is weaker between larger atoms.
Group 1 Alkali Metals
All these metals are bright and silvery, (although some must be cut to show this), some are soft (e.g. Na, K) and they all have low densities. Since these metals react by losing electrons, the group members lowest in the Table are the most reactive. (i.e. K is the most reactive out of Li, Na.
The most reactive metals are attacked by the air and water and have to be stored under oil. All the metals burn easily.
Representative equations for many of their reactions are shown below:
4Na(s) + O2(g) --> 2Na2O(s) (The same equation is written for K, Li)
2Li(s) + 2H2O(l) --> 2LiOH(aq) + H2(g) (The same for K, Na)
The Transition Metals are found in a block between Group III and Group IV in the Periodic Table.
As you go down a group, non-metals become less reactive because their atoms get bigger making it less favourable for them to gain electrons. The melting points increase because bonding is stronger between larger atoms or molecules.
Group 7 The Halogens
These non-metals are called the Halogens. (Fluorine is not studied at this level). At room temperature, chlorine is a dense green/yellow gas, bromine is a dark red/brown liquid and iodine is a shiny, black solid. At elevated temperatures Chlorine is a very pale yellow gas, Bromine is a dark brown gas and Iodine is a purple vapour. Halogen vapours are poisonous.
The most reactive member is chlorine (the smallest atom) because it accepts an electron the most easily.
Consequently, chlorine reacts quite violently with steel (iron) wool when heated but bromine reacts less readily and iodine, hardly at all.
Representative equations for some of the reactions of the Halogens are shown below:
2Fe(s) + 3Cl2(g) --> 2FeCl3(s)
Uses of Chlorine (and Iodine):
Group 0 The Noble Gases
The Noble (or inert gases) mark the end of a period.
They have filled outer electron shells and are therefore completely unreactive. They cannot accept or share electrons and so do not bond with other elements.
Whereas chlorine and hydrogen for example form diatomic molecules i.e. Cl2 and H2, the noble gases exist as discrete (i.e. single) atoms.
The forces that bond the atoms together are so weak that they exist as gases even at the lowest temperatures. In order to liquefy the gases they have to be cooled down to - 200 C so that the atoms slow down enough to make them 'stick' together.