Electron Configurations, Periodic Relationships, and Ion Formation

Vocabulary practice flashcards covering electron configurations of neutral atoms and ions, anomalous configurations, periodic table organization, blocks of elements, and the inert pair effect.

Isoelectronic

A term describing chemical species that have the exact same number of electrons and identical electron configurations, such as $Na^+$, $Al^{3+}$, and $F^-$, which all possess $10$ electrons and adopt the electron configuration of neon.

Valence electrons

The electrons in the highest principal energy levels that are removed first during cation formation and dictate the chemical reactivity and behavior of elements within a group.

Anomalous electron configurations

Electron configurations that deviate from the normal orbital-filling sequence because of the added thermodynamic stability gained by having completely half-filled subshells (such as $s^1$, $d^5$, and $f^7$) or fully filled subshells (such as $s^2$, $d^{10}$, and $f^{14}$).

Copper ($Cu$) electron configuration

An anomalous configuration written as $[Ar]\times 4s^1 3d^{10}$ rather than $[Ar]\times 4s^2 3d^9$, gaining stability from having a completely filled $3d$ subshell.

Molybdenum ($Mo$) electron configuration

An anomalous configuration written as $[Kr]\times 5s^1 4d^5$, which provides added stability by having both a half-filled $5s$ subshell and a half-filled $4d$ subshell.

Period

A horizontal row in the periodic table, traversed from left to right.

Group

A vertical column in the periodic table, labeled $1$ through $18$ under modern IUPAC nomenclature, containing elements that share the same valence electron configuration and show similar chemical reactivity.

Main group elements (Representative elements)

The elements belonging to the $s$ block and $p$ block of the periodic table, specifically groups $1$, $2$, and $13$ through $18$.

Transition metals

The elements residing in the $d$ block (groups $3$ through $12$) that lose their outer valence $s$ electrons first during ionization before losing any electrons from their $d$ subshell.

Lanthanides

The series of $4f$ inner transition elements placed beneath the main periodic table that follow the element lanthanum.

Actinides

The series of $5f$ inner transition elements placed beneath the main periodic table that follow the element actinium.

Building up principle (Aufbau principle)

The principle used to predict ground-state configurations and ion formation by sequentially filling orbitals starting from the lowest energy level up until all electrons are assigned.

Nuclear charge ($Z$)

The number of protons in the nucleus of an atom, shown in $1913$ through characteristic X-ray frequencies to be the proper ordering parameter for arranging elements in the modern periodic table.

Inert pair effect

The phenomenon in heavier elements of groups $13$ through $16$ where cations form with a charge $2$ lower than expected based on total valence electrons because the valence $s$ electrons remain unremoved as an inert pair.

Lead ($Pb$) cations

Ions formed by element $82$ ($[Xe]\times 6s^2 4f^{14} 5d^{10} 6p^2$), which can either lose all four valence electrons to form $Pb^{4+}$ ($[Xe]\times 4f^{14} 5d^{10}$) or retain its $6s^2$ electrons via the inert pair effect to form the stable $Pb^{2+}$ cation.