The atom can be divided into two main regions, the nucleus. and the electron clouds. The nucleus is home to neutrons and protons, which are the heavier subatomic particles. The mass of an atom, the atomic mass, is the sum of the number of neutrons and protons contained within the atom. The electron cloud is the region where the electrons of the atom are found.
The good thing about a dam is that electricity can be created by mechanical means. That does not affect the atmosphere. Storing such production is a different matter.
The bad thing about a dam is that it wreaks havoc on the land where the water is stored behind the dam.