Classification of Elements and Periodicity in Properties

Flashcards defining key vocabulary terms, periodic laws, classification blocks, and periodic property trends from Unit 3.

Law of Triads

A classification concept noted by Johann Dobereiner stating that in groups of three elements with similar physical and chemical properties, the middle element had an atomic weight about halfway between the other two.

Law of Octaves

A principle profounded by John Alexander Newlands in 1865 stating that when elements are arranged in increasing order of their atomic weights, every eighth element has properties similar to the first element.

Mendeleev's Periodic Law

The principle published by Dmitri Mendeleev stating that the properties of the elements are a periodic function of their atomic weights.

Eka-Aluminium

The name given by Mendeleev to a predicted undiscovered element beneath aluminium, which was later discovered and named gallium.

Eka-Silicon

The name given by Mendeleev to a predicted undiscovered element beneath silicon, which was later discovered and named germanium.

Modern Periodic Law

The law stating that the physical and chemical properties of the elements are periodic functions of their atomic numbers.

Period

A horizontal row in the Periodic Table corresponding to the highest principal quantum number ($n$) of the elements in that row.

Group

A vertical column in the Periodic Table containing elements that possess similar outer electronic configurations and chemical properties.

s-Block Elements

Elements belonging to Group 1 (alkali metals) and Group 2 (alkaline earth metals) with outermost electronic configurations of $ns^1$ and $ns^2$.

p-Block Elements

Elements belonging to Groups 13 to 18 with outermost valence shell configurations varying from $ns^2 np^1$ to $ns^2 np^6$.

Representative Elements

The combined group of elements comprising both the s-Block and p-Block elements, also known as Main Group Elements.

d-Block Elements

Elements of Groups 3 to 12 characterized by the filling of inner d orbitals, having the general outer electronic configuration $(n-1)d^{1-10} ns^{0-2}$; also called Transition Elements.

f-Block Elements

The Lanthanoids and Actinoids positioned at the bottom of the periodic table, characterized by the outer electronic configuration $(n-2)f^{1-14} (n-1)d^{0-1} ns^2$; also called Inner-Transition Elements.

Transuranium Elements

The elements appearing after uranium ($Z > 92$) in the periodic table.

Metalloids

Elements (such as silicon, germanium, arsenic, antimony, and tellurium) bordering the thick zig-zag line in the Periodic Table that show properties characteristic of both metals and non-metals; also known as Semi-metals.

Covalent Radius

Half the distance between two atoms of a non-metallic element when bound together by a single bond in a covalent molecule.

Metallic Radius

Half the internuclear distance separating adjacent metal cores in a metallic crystal.

Isoelectronic Species

Atoms and ions that contain the exact same number of electrons, such as $O^{2-}$, $F^{-}$, $Na^{+}$, and $Mg^{2+}$.

Ionization Enthalpy

A quantitative measure of the energy required to remove an electron from an isolated gaseous atom in its ground state, expressed in $kJ\,mol^{-1}$.

Electron Gain Enthalpy

The enthalpy change accompanying the process when an electron is added to a neutral gaseous atom to convert it into a negative ion.

Electronegativity

A qualitative measure of the ability of an atom in a chemical compound to attract shared electrons to itself.

Diagonal Relationship

The similarity in chemical behavior between the first element of a group in the s- or p-block and the second element of the adjacent higher group (e.g., lithium with magnesium, beryllium with aluminium).

Amphoteric Oxides

Oxides that exhibit both acidic and basic properties, behaving as acidic with bases and as basic with acids (e.g., $Al_2O_3$, $As_2O_3$).

Neutral Oxides

Oxides that possess neither acidic nor basic properties (e.g., $CO$, $NO$, $N_2O$).