Periodic Trends: Ionization Energy, Electron Affinity, and Atomic Radius

Vocabulary flashcards covering AP Chemistry periodic trends including first and stepwise ionization energies, electron affinity, atomic radii, and their respective exceptions.

Ionization energy

The amount of energy required to remove an electron from a gaseous atom or ion.

First ionization energy

The amount of energy required to remove the highest energy (least tightly bound) electron from an atom.

Stepwise ionization process

The sequential removal of electrons from an atom where the highest energy valence electrons are removed first, requiring progressively more energy for each subsequent electron removed.

Effective nuclear charge

The net positive charge experienced by valence electrons from the nucleus; it increases across a period and as electrons are removed, causing the nucleus to hold electrons more tightly.

Core electron ionization energy jump

A dramatic increase between consecutive ionization energies (such as between the third and fourth ionization energy for aluminum) indicating that all valence electrons have been removed and electrons are now being pulled from core shells.

Periodic trend of first ionization energy (across a period)

First ionization energy increases from left to right across a period because additional protons increase the effective nuclear charge while electrons are added to the same energy level.

Periodic trend of first ionization energy (down a group)

First ionization energy decreases down a group because electrons are removed from shells located further from the nucleus, requiring less energy.

First ionization energy exception (Beryllium to Boron)

The unexpected decrease in ionization energy from beryllium to boron caused by removing boron's electron from the higher energy $2p$ sublevel compared to beryllium's lower energy $2s$ sublevel.

First ionization energy exception (Nitrogen to Oxygen)

The decrease in first ionization energy from nitrogen to oxygen caused by electron-electron repulsion between paired electrons in the $2p$ orbital of oxygen, making that electron easier to remove.

Electron affinity

The energy change associated with the addition of an electron to a gaseous atom, typically an exothermic process with negative enthalpy values.

Periodic trend of electron affinity (across a period)

Electron affinity increases and values become more negative from left to right across a period, meaning more energy is released when an electron is added.

Electron affinity exception (Carbon to Nitrogen)

The decrease in electron affinity from carbon to nitrogen where the value becomes positive because adding an electron to nitrogen forces it into an already occupied $2p$ orbital, requiring energy to overcome electron-electron repulsion.

Atomic radius

A measure of atomic size obtained from half the distance between atoms in a covalent bond or half the distance between metal atoms in solid metal crystals.

Periodic trend of atomic radius (across a period)

Atomic radius decreases from left to right across a period because an increasing number of protons increases the effective nuclear charge, pulling valence electrons closer to the nucleus.

Periodic trend of atomic radius (down a group)

Atomic radius increases moving down a group because additional shells of electrons are added, increasing the overall size of the orbitals.

Electronegativity trend

The periodic property that increases across a period and increases up a group, with fluorine being the most electronegative element.