Both are almost equal in mass, 1 amu (atomic mass unit). Another subatomic particle in the atom is the electron. It is negatively charged and it's mass is about 2000 times smaller than that of a neutron or electron. Usually the number or electron in an atom is the same as the number of protons. So, usually the atoms have not a positive nor negative charge, but they are neutral. Electron are not in the nucleus like the protons and neutrons are. They travel at very high speeds throughout the atom in energy levels. The energy levels are like orbits that surround the nucleus. The number of protons that are in the nucleus of an atom is called the atomic number. The atomic number identifies the atom because no two atoms have the same number of protons in there nucleus. For example, hydrogen has the atomic number of 1, that means all atoms that have one proton in its nucleus is hydrogen. The atomic mass number is the number of neutrons and protons in the nucleus. To find the number on neutrons in an atom, you must round the atomic mass number to the nearest whole number and then subtract the atomic number. Remember the atomic number is the same as the number of protons in the atom. To find out the number or electrons an atom contains, you just need to know the atomic number because there is the same number of protons as there is electrons in atoms. For example, in sodium, the atomic number is 11, and the atomic mass number is 22.98977. This means that sodium contains 11 protons, 11 electron, and 12 neutrons. (See Figure 1) Substances known as elements are made up of solely on type of atom. Scientists have discovered 109 elements, 90 were found in nature, and 19 were artificially made in laboratories by scientists. Each element is represented by a chemical symbol. Each symbol is made up of one or two letters, usually taken from the name of the element. The symbol of oxygen is O, the symbol for phosphorus is P, and the symbol for Nitrogen is N.