A carbon atom attached to four different groups is considered chiral. This means it has a non-superimposable mirror image, like your left and right hands.

Here's why:

* Chirality: A molecule is chiral if it has a non-superimposable mirror image.

* Tetrahedral Geometry: Carbon atoms form four bonds, usually arranged in a tetrahedral shape.

* Four Different Groups: If all four groups attached to the carbon are different, the molecule will have a mirror image that cannot be superimposed on the original.

Example:

Consider a carbon atom attached to:

1. A hydrogen atom (H)

2. A methyl group (CH3)

3. An ethyl group (CH2CH3)

4. A chlorine atom (Cl)

This carbon atom is chiral because it has four different groups attached to it.

However, if a carbon atom is attached to four other carbon atoms, it is not chiral. All four groups are the same (carbon), making the molecule achiral.