Chemical element by symbol, as well as ionization energies of the elements. The nuclides of stable and radioactive elements are also available as a list of nuclides, sorted by length of half-life for those that are unstable. One of the most convenient, and certainly the most traditional presentation of the elements, is in the form of the periodic table, which groups together elements with similar chemical properties (and usually also similar electronic structures). The atomic number of an element is equal to the number of protons in each atom, and defines the element. For example, all carbon atoms contain 6 protons in
Relative atomic mass Relative atomic mass Relative atomic mass (symbol: "A") or atomic weight is a dimensionless physical quantity defined as the ratio of the average mass of atoms of a chemical element in a given sample to one unified atomic mass unit. The unified atomic mass unit (symbol: "u" or "Da") is defined as being of the atomic mass of a carbon-12 atom. Since both values in the ratio are expressed in the same unit ("u"), the resulting value is dimensionless; hence the value is said to be "relative". For a single given sample, the relative atomic mass of a given element