Metals and Non-Metals
Classification of Elements According to Properties
Elements display very different properties depending on their position in the Periodic Table. How and why are some called metals and some non-metals?
All chemicals elements are contained in the Periodic Table. This table arranges the elements according to their electronic structure. One of the clearest ways to define elements is whether they are metals or non metals. What is the difference? How can we define a metal or a non-metal?
Hard and Shiny?
Most people would say that metals are shiny and hard. Some would mention that metals conduct electricity. When you think about metals, however, you soon realise that metals are quite different from one another. Iron is a hard shiny metal. Mercury is a liquid. Lead is a dull grey and easy to bend. Copper is a coppery colour!
Poisonous Gases?
Non-metals, too, are very different from one another. Some are colourless gases like oxygen or nitrogen. Chlorine is a green gas and poisonous. Carbon has more than one form. Sulphur is a yellow solid. Chemists need to work out what properties put elements in one or other of these categories.
Periodic Table
A look at the periodic table helps with these problems. The metals are all on the left-hand side of the periodic table and in the transition metals section in the middle. To the right of the transition metals a line in the form of steps can be drawn, beginning between boron and aluminium and going down between silicon and germanium and so on.
Metal Properties
Metals in the form of elements are usually good conductors of electricity, are flexible and strong. When they are combined with oxygen to form oxides, they are alkaline compounds. When combined with chlorine to form chlorides they form ionic compounds which have giant structures.
Non-Metal Properties
Non-metals as elements are rarely solids, usually they are gases. They are poor conductors of electricity except graphite which has a special structure. Their oxides are often gases and are acidic. Their chlorides are covalently bonded and solids or liquids.
Electronic Expalantion
These properties can be simply explained by considering the electronic structure of the atoms of these elements. Metals, on the left hand side of the periodic table, have few electrons in the outer shell. This lends itself to what is called metallic bonding in which many atoms of the elements share their outer electrons in a delocalised cloud which makes a hard structure which conducts electricity. Non-metals have outer electron shells which are nearly full. This means that small numbers of atoms bond covalently to form small molecules which usually are gases.
Shared Electrons
Again, combined with oxygen and chlorine, metals lose electrons and become positive ions, leading to alkaline oxides and ionic chlorides. Non-metals have to share electrons to fill their outer shell and so form small covalently bonded molecules with oxygen and chlorine which again are often gases or liquids.
The classification of elements into metal and non-metal groups is a useful exercise and helps a great deal in understanding the properties of different elements and compounds.
