Calcium Carbide

3D Model

A free carbon atom has 6 electrons: 2+4. It needs 4 more to have 8 in the last shell.

A free calcium atom has 20 electrons: 2+8+8+2. The two outermost electrones are loosely attached to the core, for the nucleus is fully surrounded by 18 electrons.

When you heat coal and limestone, the 2 electrons get enough energy to leave the calcium atom and join carbon. In this way a calcium carbide crystal is formed.

In the first model you can see a traditional 2D representation of bonds in CaC2. The two outermost electrons have left the calcium atom. Now it is a positive ion. They participate in bonds between two coal atoms which together form a negative ion.

The second model shows how pairs of electrons occupy space. Carbon atoms are connected by one sigma and two pi bonds. Each pi bond consists of two shapes resembling a banana, while the sigma bond is a round shape between them.

Orbitals in carbon are coloured gray and the ones in calcium green.

The third model treats atoms as balls.