Why does the black sphere in molecular modeling kits have 4 holes?

Answer 1

The black spheres in a molecular modeling kit represent carbon which can have up to four bonds.

Answer 2

The black sphere in molecular modeling kits represents a carbon atom, which can form up to four chemical bonds due to its atomic structure and electron configuration. The four holes represent the four locations where the carbon atom can share or receive electrons to form these bonds with other atoms.