Final answer:
With four electron groups around a central atom, the molecule usually adopts a tetrahedral geometry if all groups are atoms, but other shapes like trigonal pyramidal or bent can form if there are lone pairs or double bonds.
Step-by-step explanation:
When a central atom has four "things" (electron groups) attached to it, it can exhibit different shapes based on the actual constituents attached to these electron groups. In a condition where there are four atoms and no lone pairs bonded to the central atom, the molecule typically adopts a tetrahedral geometry, such as in methane (CH4).
In situations where there are lone pairs involved, or a combination of double bonds and atoms, the geometry can differ, resulting in structures like trigonal pyramidal or bent