If diamond and graphite are made of carbon, then why do they look different, and why is diamond harder than graphite?
Diamond and graphite are two allotropic forms of Carbon. But still these are very different from one another.
1 Diamond :- In this case each carbon is surrounded by other four carbon atoms in such a way that together they make a network like structure which give to a giant molecule. Every atom is held strongly.
Due to this reason the diamond is one of the hardest substance.
As all the four electrons of carbon are utilized in bond formation, no electron is free. So the diamond do not conduct electricity.
2 Graphite :- In case of graphite , it has hexagonal arrangement of C-atoms in which every atom of carbon is attached only to the three atoms. And the hexagonal rings are present in the forms of sheets. These sheets are staked on one another with weak forces of attraction.
Due to weak forces of attraction between the hexagonal layers, they can slide over each other. So graphite is soft.
Secondly only three electrons are utilized in bond formation. The one free electron is responsible for the conduction of electricity. Thus it is a good conductor of electricity.