Periodic Table Trends and Atomic Properties

Comprehensive vocabulary flashcards covering periodic table organization, periodic trends, atomic and ionic radii, ionization energies, electron affinities, and electronegativity based on lecture notes.

Periodic Table

An organized display of chemical elements arranged in order of increasing atomic number.

Dmitri Mendeleev

The chemist who developed the periodic table in 1869 by arranging elements according to increasing atomic mass and predicted the properties of undiscovered elements.

Henry Moseley

The physicist who discovered in 1911 that the atomic number (number of protons) is the fundamental basis for periodic table organization.

Period (Series)

A horizontal row on the periodic table.

Group (Family)

A vertical column on the periodic table containing elements with similar chemical properties.

Alkali Metals

Group 1 elements ($s$-block) that are highly reactive with water and nonmetals, do not occur in pure form in nature, and derive their name from an Arabic word meaning 'basic' (e.g., $Na_2O + H_2O \rightarrow 2NaOH$).

Alkaline Earth Metals

Group 2 elements ($s$-block) that do not exist in pure form in nature and react with water to form basic solutions (e.g., $CaO + H_2O \rightarrow Ca(OH)_2$).

Transition Metals

Groups 3–12 elements that all have an $s^2$ valence electron configuration except Chromium ($Cr$) and Copper ($Cu$), which have $1$ valence electron; they are less reactive than Groups 1 and 2.

Halogens

Group 17 elements ($p$-block) that are the most reactive nonmetals because they require only $1$ electron to achieve a stable noble gas configuration, reacting with metals to form salts.

Salt

An ionic compound consisting of a cation ($+$) bonded to an anion ($-$), typically formed from a metal bonded to a nonmetal.

Noble Gases

Group 18 non-reactive elements possessing a full octet of $8$ valence electrons, with the exception of Helium ($He$), which has $2$ valence electrons.

Lanthanides

Inner transition and rare earth elements with atomic numbers $58$ to $71$ that belong to the $4f$ block.

Actinides

Inner transition elements with atomic numbers $90$ to $103$ that belong to the $5f$ block, organized and discovered by Glenn Seaborg.

Effective Nuclear Charge ($Z_{eff}$)

The net positive charge experienced by an electron in a polyelectronic atom as protons attract electrons while inner electrons shield outer electrons.

Shielding (Shielding Effect)

The phenomenon where inner core electrons block or compete for the attractive force of the nucleus, preventing it from fully reaching the valence electrons.

Bonding Radius (Atomic Radius)

Half the distance between the two nuclei of identical bonding atoms.

Ion

An atom or group of atoms that possesses a positive or negative charge resulting from the loss or gain of electrons.

Ionization

The process of forming an ion by gaining or losing electrons.

Cation

A positively charged ion formed by losing electrons; it is always smaller than its neutral parent atom because reduced electron-electron repulsion allows the cloud to contract.

Anion

A negatively charged ion formed by gaining electrons; it is always larger than its neutral parent atom because increased electron-electron repulsion forces the electron cloud to expand.

Ionization Energy (IE)

The energy required to remove an electron from a neutral gas-phase atom in an endothermic process ($A_{(gas)} + \text{energy} \rightarrow A^+_{(gas)} + e^-$).

Successive Ionization Energies

The step-by-step removal of electrons from an atom or ion, which requires a massive jump in energy once a full noble gas configuration is disrupted.

Electron Affinity (EA)

The energy change that takes place when an electron is acquired by a neutral atom in the gas phase.

Exothermic Electron Affinity (Negative EA)

A desirable process in which an atom releases energy upon gaining an electron ($A + e^- \rightarrow A^- + \text{energy}$), yielding a negative value and reaching a lower, more stable energy state.

Endothermic Electron Affinity (Positive EA)

An unfavorable process in which energy must be absorbed for an atom to gain an electron ($A + e^- + \text{energy} \rightarrow A^-$), yielding a positive value and creating an unstable state typical of noble gases.

Ionic Radius

The size of an atom's ion after gaining or losing electrons.

Iso-electronic

A term describing atoms and ions of different elements that share the exact same number of electrons (e.g., $Mg^{2+}$ and $Na^+$, which each have $10\,e^-$).

Electronegativity (EN)

The ability of an atom in a chemical bond to attract shared bonding electrons toward itself.

Nitrogen vs. Oxygen Ionization Energy Exception

An anomaly where Nitrogen has a higher first ionization energy ($1402\,kJ\,mol^{-1}$) than Oxygen ($1314\,kJ\,mol^{-1}$) because Nitrogen's half-filled $2p$ subshell ($\uparrow\uparrow\uparrow$) minimizes repulsion, whereas Oxygen's paired $2p$ electrons ($\uparrow\downarrow\uparrow\uparrow$) create electron-electron repulsion that makes electron removal easier.