Carbon, silicon, germanium, tin and lead are all members of group 14 of the periodic table. Carbon is a non-metal, silicon and germanium are metalloids, and tin and lead are metals. The trend is towards an increasingly metallic character.
Boiling and melting points generally fall as we descend the group. Carbon melts at 3550 degrees Celsius and silicon melts at 1414 degrees Celsius. Tin and lead, with their figures of 231.97 degrees Celsius and 327.5 degrees Celsius, have particularly low melting points for metals. These metals are also especially soft. The carbon allotrope, diamond, is the hardest of all elements.
Graphite, another allotrope of carbon, is a good conductor of electricity. Both silicon and germanium possess semiconductor properties; that is, their ability to conduct electricity lies somewhere between that of metals and that of insulators, and can be controlled by adjusting factors such as temperature and the presence of impurities. They are used in electronics.
Carbon and silicon combine to form silicon carbide, a substance of great hardness, only marginally softer than diamond.
The reactivity of the elements tends to increase as we descend the group, although lead is inert because of the protective layer it forms on exposure to air.
