Atoms Atoms make up the chemical elements. Each chemical element has nearly identical atoms. Each element has the same number of protons and the same number of electrons. Number of electrons. Isotopes are atoms of the same element with differing numbers of neutrons.
Some isotopes are unstable which results in radioactivity.
Every atom of K has 19 protons. Some atoms of K have 20 neutrons, others have 21, and others have 22. 40 K is radioactive and decays to 40 Ar and 40 Ca. Structure of Atoms Electrons orbit around the nucleus in different shells, labeled from the innermost shell as K, L, M, N, etc. Each shell can have a certain number of electrons.