A metal is a chemical element that is a good conductor of both electricity and heat and forms cations and ionic bonds with non-metals. Cations are usually formed by electron loss. They are classified as alkali metals, alkali earth metals, transition metals (the classic metals), post-transition metals, lanthanides, and actinides.A nonmetal is an element in groups 14 to 18 of the Periodic Table (group 17 are halogens and group 18 noble gases). Nonmetals are not able to conduct electricity or heat very well. As opposed to metals, non-metallic elements are very brittle, and cannot be rolled into wires or pounded into sheets. The nonmetals exist in two of the three states of matter at room temperature: gases (such as oxygen) and solids (such as carbon). The nonmetals have no metallic luster, and do not reflect light. They have oxidation numbers of ±4, -3, and -2.Basic differencesMetallic compounds conduct electricity and heat while non-metallic compounds are less conductive.Most metallic compounds are solid at room temperature (except Mercury and gallium which are liquids). Nonmetals may be solid or gas.Metallic compounds are hard and malleableMetals generally have higher melting and boiling points.Metals are electropositive while nonmetals are electronegative.Metals have 1, 2 or 3 electrons in the outermost shell while nonmetals have 4 to 8 electrons in the outermost shell.On electrolysis of metal compounds, metals are discharged at the cathode. On electrolysis of compounds, non-metals are discharged at the anode.Transition Metals (classic metals)There are 38 elements in groups 3 through 12 of the Periodic Table called "transition metals". As with all metals, the transition elements are both ductile and malleable, and conduct electricity and heat. The interesting thing about transition metals is that their valence electrons, or the electrons they use to combine with other elements, are present in more than one shell. This is the reason why they often exhibit several common oxidation states. There are three noteworthy elements in the transition metals family. These elements are iron, cobalt, and nickel, and they are the only elements known to produce a magnetic field.