Periodic Properties of the Elements

Vocabulary practice cards focusing on periodic trends, effective nuclear charge, atomic and ionic radii, successive ionization energies, and electron affinity.

Pseudo core electrons

Electrons in inner $d$ orbitals that initially behave as core electrons, but can be ionized along with valence $s$ electrons, particularly in transition metal ions such as $Fe^{3+}$.

Effective nuclear charge ($Z_{eff}$)

The net positive nuclear charge experienced by outer electrons, defined quantitatively as the actual nuclear charge ($Z$) minus the shielding constant ($\sigma$).

Shielding constant ($\sigma$)

A screening value representing the reduction of full nuclear charge felt by outer electrons due to electron-electron repulsion; core electrons provide significantly greater shielding than valence electrons do for each other.

Atomic radius

Half the distance between the nuclei of two neighboring identical atoms of the same element; it decreases across a period from left to right and increases down a group.

Metallic radius

The radius determined by measuring the distance between two neighboring identical metal atoms in a metallic solid.

Covalent radius

The radius determined from the distance between neighboring identical atoms bonded in a chemical compound.

Ionic radius

The effective radius of an ion in an ionic compound determined through X-ray diffraction measurements; cations are always smaller than their parent neutral atoms, whereas anions are always larger.

Isoelectronic

A term describing atoms or ions that share identical electron counts and electron configurations (such as $Rb^+$, $Sr^{2+}$, $Se^{2-}$, and $Br^-$, all having $36$ electrons).

First ionization energy ($IE_1$)

The amount of energy required to remove the highest energy electron from an isolated atom in the gaseous state ($\text{Energy} + X_{(g)} \rightarrow X^+_{(g)} + e^-$).

Second ionization energy ($IE_2$)

The energy required to remove an electron from an isolated, singly charged cation in the gaseous state ($X^+_{(g)} + \text{Energy} \rightarrow X^{2+}_{(g)} + e^-$); it is always greater than the first ionization energy.

Subshell stability anomaly

Minor periodic dips in ionization energy trends across a period caused by the exceptional stability of fully filled (e.g., $s^2$) or half-filled (e.g., $p^3$) electron subshells.

Successive ionization energy jump

A massive, order-of-magnitude increase between successive ionization energies that occurs when an electron must be removed from an inner core shell after achieving a stable noble gas configuration.

Electron affinity ($EA$)

The measure of energy change when an electron is added to an isolated atom in the gaseous state to form an anion; values are generally negative, signifying that energy is released during favorable anion formation.