1. Every atom is composed of positively charged nucleus surrounded by negatively charged electrons.

3. Protons and neutrons compose the nucleus. (The common form of the hydrogen atom, which has no neutron, is the only exception). Protons are about 1800 times more massive than electrons, but they carry out an amount of positive charge equal to the negative charge of electrons. Neutrons have slightly more mass than protons and have no net charge.

Atoms.

2. The elections of all molecules are identical. Each has the same quantity of negative charge and the same mass.

4. Atoms usually have as many electrons as protons, so the atom has zero net charge.