Electronegativity, symbol χ, is a chemical property that says how well an atom can attract electrons towards itself. The electronegativity of an atom is influenced by the atom's atomic number and the distance between the atom's valence electrons (the outermost electrons that take part in chemical bonding) and its nucleus. It was first theorised by Linus Pauling in 1932 as part of his valence bond theory, and is related to other chemical properties. Generally, electronegativity increases from the bottom-left to the upper-right of the periodic table; this is known as a periodic trend.