The structure of atoms Chemistry is the science of matter, the physical material that makes up everything in the universe. Matter is anything that takes up space and has a measurable amount of substance, or mass. Although scientists know a great deal about atoms, a simplified explanation provides a good starting point in understanding their complex structures. Every atom is made up of particles smaller than the atom itself. Protons and neutrons are found at the core, or nucleus, of the atom.
Electrons surround the nucleus.
Neutrons , although similar to protons in mass, are neutral and carry no charge. For this reason, the atomic mass of an atom is defined as the combined mass of all its protons and neutrons without regard to its electrons. The identity of an atom is determined by its number of protons. For example, an atom containing two protons is helium, a gas you have probably seen used to blow up balloons. The number of protons in each type of element is also listed in this table and is called the atomic number .