Periodicity and Periodic Table Vocabulary

Vocabulary flashcards summarising key terms and trends related to the periodic table, periodicity, and elemental properties.

Periodicity in properties

The recurring similarity of element properties when the elements are arranged in order of increasing atomic number.

Atomic number

The number of protons in the nucleus of an atom; determines an element’s identity and position in the Periodic Table.

Electronic configuration

The distribution of electrons among the shells and subshells of an atom.

Valence shell

The outermost electron shell of an atom containing the electrons involved in bonding.

Valency

The combining capacity of an element, equal to the number of electrons it gains, loses or shares.

Period (Periodic Table)

A horizontal row in the Periodic Table; the number of occupied electron shells equals the period number.

Group (Periodic Table)

A vertical column in the Periodic Table; elements share the same number of valence electrons and similar properties.

Alkali metal

Group 1 element with one valence electron; soft, highly reactive, strong reducing agent that forms strong alkalis.

Alkaline earth metal

Group 2 element with two valence electrons; harder than alkali metals and form basic oxides and hydroxides.

Transition metal

Element in the d-block (groups 3-12) that forms colored ions and variable oxidation states.

Halogen

Group 17 non-metal with seven valence electrons; strong oxidising agent that forms salts with metals.

Noble gas

Group 18 element with a full valence shell; chemically inert with zero valency.

Bridge element

Element of period 2 that shows diagonal similarity with the element of period 3 in the next group (e.g., Li–Mg).

Diagonal relationship

Resemblance between certain period-2 elements and the diagonally positioned period-3 elements of the next group.

Atomic radius

The distance from the nucleus to the outermost electron shell of an atom.

Ionisation potential (Ionisation energy)

Energy needed to remove one electron from a gaseous atom to form a cation (unit: eV).

Electron affinity

Energy released when a gaseous atom accepts an electron to form an anion.

Electronegativity

A measure of an atom’s ability to attract the shared pair of electrons in a chemical bond.

Reducing agent

Substance that readily loses electrons; alkali metals are strong reducing agents.

Oxidising agent

Substance that readily gains electrons; halogens are strong oxidising agents.

Electropositive element

Element that readily loses electrons to form positive ions; characteristic of metals like alkali metals.

Electronegativity trend across a period

Increases from left to right due to decreasing atomic radius and increasing nuclear charge.

Electronegativity trend down a group

Decreases down a group because increasing atomic size outweighs the increase in nuclear charge.

Electron affinity trend across a period

Generally increases left to right; halogens have the highest values, alkali metals the lowest.

Electron affinity trend down a group

Generally decreases down a group as atomic size increases.

Ionisation potential trend across a period

Increases from left to right due to decreasing atomic size and stronger nuclear attraction.

Ionisation potential trend down a group

Decreases down a group because atomic size increases and valence electrons are less tightly held.

Ionic bond

Chemical bond formed by the transfer of electrons, producing electrovalent compounds such as NaCl.

Covalent bond

Chemical bond formed by sharing electron pairs between atoms, typical in non-metal compounds like SiCl₄.

Amphoteric oxide/hydroxide

Compound that reacts with both acids and bases, e.g., Al(OH)₃.

Basic oxide/hydroxide

Oxide or hydroxide that reacts with acids to form salt and water; characteristic of metals like Na₂O, NaOH.

Acidic oxide/hydroxide

Oxide or hydroxide that reacts with bases; typical of non-metals, e.g., SO₃, H₂SO₄.

Electrovalent compound

Compound formed through ionic bonding between metals and non-metals.

Atomicity

Number of atoms present in one molecule of an element (e.g., halogens are diatomic).

Stable noble-gas configuration

Electronic arrangement with a complete valence shell (ns²np⁶) giving zero electron affinity and high stability.