Heat is added to an element causing the atoms to bounce back and forth in the molecule. this is an example of which type of motion?

The back and forth bouncing of atoms in the molecule on addition of heat is defined as vibration type of motion.

Explanation:

The atoms are the building blocks of each elements. And elements combine to form molecules. So the atoms will be arranged in a periodic order in the molecules. At room temperature, the atoms in the molecule will remain at its ground state with minimum energy stored in them.

But when the molecule is heated, the atoms will attain thermal energy and they will start to move slightly in their places. Their movement can be visualized as bouncing back and forth in their positions. So this kind of bouncing with the fixed center is termed as vibration motion.