What does an atomic number of an element tell you?
The full chemical symbol for an element shows its mass number at the top, and its atomic number at the bottom. This symbol tells you that the chlorine atom has 17 protons. It will also have 17 electrons, because the number of protons and electrons in an atom is the same.
The atomic number represents or stands for the distinct identity of a chemical element. It is usually defined as the number or protons present in an atom of an element, which is also equal to the number of electrons.
- Atomic number is the number of protons, and therefore also the total positive charge, in the atomic nucleus. The Rutherford–Bohr model of the hydrogen atom (Z = 1) or a hydrogen-like ion (Z > 1).
- click on any element's name for further chemical properties, environmental data or health effects. This list contains the 118 elements of chemistry. For chemistry students and teachers: The tabular chart on the right is arranged by Atomic number.
- A property closely related to an atom's mass number is its atomic mass. The atomic mass of a single atom is simply its total mass and is typically expressed in atomic mass units or amu. By definition, an atom of carbon with six neutrons, carbon-12, has an atomic mass of 12 amu.
Updated: 26th October 2019