Concept Summary

The Periodic Table of the Elements organizes the elements according to their atomic numbers and reveals a pattern of similar chemical and physical properties among elements.
- Rows are called periods and are based on the same principal energy level, n.
- Columns are called groups. Elements in the same group have the same valence shell electron configuration.

The elements on the periodic table belong to one of three types.
- Metals are shiny (lustrous), conduct electricity well, and are malleable and ductile. Metals are found on left side and middle of the periodic table.
- Nonmetals are dull, poor conductors of electricity, and are brittle. Nonmetals are found on right side of the periodic table.
- Metalloids possess characteristics of both metals and nonmetals and are found in a stair-step pattern starting with boron (B).

Effective nuclear charge (Z_eff) is the net positive charge experienced by electrons in the valence shell and forms the foundation for all periodic trends.
- Z_eff increases from left to right across a period, with little change in value from top to bottom in a group.
- Valence electrons become increasingly separated from the nucleus as the principal energy level, n, increases from top to bottom in a group.
Atomic radius decreases from left to right across a period and increases from top to bottom in a group.
Ionic radius is the size of a charged species. The largest nonmetallic ionic radii and the smallest metallic ionic radii exist at the metalloid boundary.
- Cations are generally smaller than their corresponding neutral atom.
- Anions are generally larger than their corresponding neutral atom.
Ionization energy is the amount of energy necessary to remove an electron from the valence shell of a gaseous species; it increases from left to right across a period and decreases from top to bottom in a group.
Electron affinity is the amount of energy released when a gaseous species gains an electron in its valence shell; it increases from left to right across a period and decreases from top to bottom in a group.
Electronegativity is a measure of the attractive force of the nucleus for electrons within a bond; it increases from left to right across a period and decreases from top to bottom in a group.

Alkali metals typically take on an oxidation state of +1 and prefer to lose an electron to achieve a noble gas-like configuration; they and the alkaline earth metals are the most reactive of all metals.
Alkaline earth metals take on an oxidation state of +2 and can lose two electrons to achieve noble gas-like configurations.
Chalcogens take on oxidation states of −2 or +6 (depending on whether they are nonmetals or metals, respectively) in order to achieve noble gas configuration. They are very biologically important.
Halogens typically take on an oxidation state of −1 and prefer to gain an electron to achieve noble gas-like configurations; these nonmetals have the highest electronegativities.
Noble gases have a fully filled valence shell in their standard state and prefer not to give up or take on additional electrons; they have very high ionization energies and (for He, Ne, and Ar), virtually nonexistent electronegativities and electron affinities.
Transition metals are unique because they take on multiple oxidation states, which explains their ability to form colorful complexes with nonmetals in solution and their utility in certain biological systems.