ABSTRACT
Periodic table: The term has come to stand on its own as conveying nothing more than “the purposeful arrangement of the 118 elements of chemistry into rows and groups.” But the periodic table was developed and named because of the regular, repeating (periodic) pattern in chemical properties. The repetition of properties was the original criterion for determining what elements appeared together in the same group. In part, this periodic pattern in chemical properties is the result of the repeating pattern in electron configurations (Chapter 8). In this chapter, we consider trends in atomic radius, ionization energy, electron affinity, and electronegativity. The pattern in these properties can be explained by using the electron configurations of the elements and by using Coulomb's law. Coulomb's law defines the attraction between the positively charged nucleus and a negatively charged valence electron. The trends of size, ionization energy, and electron affinity are highly related. For example, carbon is a smaller atom that has a higher ionization energy and higher electron affinity, while lead is a larger atom that has a lower ionization energy and a lower electron affinity. Electronegativity is a composite property that is connected to atomic size, ionization energy, and electron affinity and is defined as the power of an atom to attract electrons to itself. Electronegativity provides a powerful tool for analyzing and understanding molecular properties and chemical reactions.
