Even More About the Periodic Table Periodic Trends

Trends in Atomic Size Atomic radius - one-half the distance between the nuclei of two atoms of the same element when the atoms are joined In general, atomic size increases from top to bottom within a group and decreases from left to right across a period.

Trend in Ionic Size Cations are always smaller than the atoms from which they form. Anions are always larger than the atoms from which they form.

Trends in Ionization Energy First ionization energy tends to decrease from top to bottom within a group and increase from left to right across a period.

Trends in Electronegativity In general, electronegativity values decrease from top to bottom within a group. For representative elements, the values tend to increase from left to right across a period.

Summary of Trends The trends that exist among these properties can be explained by variations in atomic structure. The increase in nuclear charge within groups and across periods explains many trends. Within groups an increase in shielding (distance from the nucleus) has a significant effect

Ionization energy INCREASES Electronegativity INCREASES Atomic size DECREASES Ionization energy INCREASES Electronegativity INCREASES Nuclear charge INCREASES Shielding is constant 1 18 2 13 14 15 16 17 Ionization energy DECREASES Electronegativity DECREASES Nuclear charge INCREASES Atomic size INCREASES Shielding INCREASES Ionic size INCREASES Size of cations decreases Size of anions decreases

Periodic Trends Notes

Electron Shells Ground State means no electrons are where they are not supposed to be. Excited state is when the electrons absorb energy and jump up to a higher electron shell or energy level. When electrons fall back down to the ground state they emit a specific amount of energy which is noticed as a specific color (or colors) of light.