There are also chemical reactions that require the input of energy. An example is photosynthesis, in which carbon dioxide and water are combined to form plant material and molecules of oxygen. The energy for this chemical reaction is provided by sunlight. Chemical reactions do not change the nature of atoms, in contrast to nuclear reactions. Electron Elementary particle of negative electric charge and a mass that is only about 0.0005 that of the proton .
Electrons are basic constituents of atoms .
Energy A measure of being able to do work. There are many forms of energy, such as heat, mechanical, electrical, radiant, chemical, and nuclear energies. To escape would require a speed greater than that of light , which is not allowed. An attractive force between matter. For instance, gravity holds the planets together, keeps us on the surface of the Earth, and keeps the planets in orbit around the Sun .