AP Chemistry Study Guide: Periodic Trends and Ionic Properties

Coulomb’s Law

Describes the force of attraction or repulsion between charged particles (F ∝ Q1 Q2/r²).

Effective Nuclear Charge (Z_eff)

The net positive charge experienced by valence electrons, less than the actual nuclear charge due to shielding from inner electrons.

Atomic Radius

Half the distance between the nuclei of two identical atoms bonded together.

Ionization Energy (IE)

The energy required to remove the outermost electron from a gaseous atom in its ground state.

Electronegativity

The ability of an atom's nucleus to attract shared electrons in a chemical bond.

Electron Affinity

The energy change that occurs when an electron is added to a gaseous atom.

Isoelectronic Series

A group of ions/atoms that have the same electron configuration.

Trend Across a Period for Atomic Radius

Decreases due to higher Z_eff pulling the electron cloud tighter towards the nucleus.

Trend Down a Group for Atomic Radius

Increases; new principal energy levels added, increasing distance.

Trend Across a Period for Ionization Energy

Increases; higher Z_eff and smaller radius means more energy is needed to remove an electron.

Trend Down a Group for Ionization Energy

Decreases; valence electrons are further away from the nucleus.

Group 2 to Group 13 Ionization Energy Exception

Boron has lower IE than Beryllium because its electron is from a higher energy subshell (2p > 2s).

Group 15 to Group 16 Ionization Energy Exception

Oxygen has lower IE than Nitrogen due to electron-electron repulsion in the paired 2p orbitals.

Cations

Ions that are smaller than their parent atoms due to loss of the outermost shell.

Anions

Ions that are larger than their parent atoms due to addition of electrons causing repulsion.

Lattice Energy

The energy required to completely separate one mole of a solid ionic compound into its gaseous ions.

Trends in Lattice Energy

Higher ionic charges lead to stronger attractions and higher lattice energies.

The Rule of Isoelectronic Series Radius

As the number of protons increases, the ionic radius decreases for ions with the same number of electrons.

Core Electrons

Inner electrons that shield valence electrons from the full nuclear charge.

Valence Electrons

Electrons in the outermost shell of an atom that determine its chemical behavior.

Charge Magnitude (Q)

Dominant factor in determining lattice energy; higher charges mean stronger attraction.

Ionic Radius of Na⁺ vs K⁺

Na⁺ has a higher lattice energy than K⁺ due to smaller ionic radius.

The Impact of Electron Repulsion in Anions

Increased electron-electron repulsion causes anions to expand compared to their parent atoms.

Noble Gases and Electronegativity

Noble gases generally do not have electronegativity values because they rarely bond.

The Importance of Z_eff in Chemistry

Effective Nuclear Charge influences atomic radius, ionization energy, and other periodic trends.

Common Mistake in Chemistry Explanations

Avoid anthropomorphizing atoms; explain stability in terms of energy rather than emotions.