Every element has a set of particular characteristics. Each has a unique atomic and mass number because they contain a different ratio of protons and neutrons. The number of protons in an element mirrors the element's atomic number. The mass number equals the sum of the element's protons and neutrons.
According to increasing atomic numbers, chemical elements get organized. Periods and groups are the names of the horizontal rows and vertical columns, respectively. The chemical characteristics of elements within the same group are comparable due to their similar valency and number of outer electrons.