Periodic Table Trends Visual Master Cheat Sheet

Key Facts

• Atomic radius generally decreases from left to right across a period because $Z_{\text{eff}}$ increases and pulls valence electrons closer.
• Atomic radius generally increases down a group because the highest occupied energy level increases, such as from $n = 2$ to $n = 3$.
• Ionization energy is the energy needed to remove an electron, shown by $X(g) \rightarrow X^{+}(g) + e^{-}$.
• First ionization energy generally increases across a period and decreases down a group because electron attraction changes with $Z_{\text{eff}}$ and shielding.
• Electronegativity measures how strongly an atom attracts shared electrons in a bond, and it generally increases toward fluorine, $F$.
• Electron affinity is the energy change when an atom gains an electron, shown by $X(g) + e^{-} \rightarrow X^{-}(g)$.
• Cations are smaller than their neutral atoms because losing electrons reduces electron repulsion and can remove an outer energy level.
• Anions are larger than their neutral atoms because gaining electrons increases electron repulsion within the valence shell.

Vocabulary

Atomic radius

Atomic radius is a measure of the size of an atom, often based on half the distance between nuclei of two bonded identical atoms.

Effective nuclear charge

Effective nuclear charge, $Z_{\text{eff}}$, is the net positive charge felt by valence electrons after shielding by inner electrons.

Shielding

Shielding is the blocking effect inner electrons have on the attraction between the nucleus and valence electrons.

Ionization energy

Ionization energy is the energy required to remove an electron from a gaseous atom or ion.

Electronegativity

Electronegativity is the ability of an atom in a chemical bond to attract shared electrons toward itself.

Ionic radius

Ionic radius is the size of an ion after an atom has gained or lost electrons.