Class 11 Chemistry: Classification of Elements and Periodicity in Properties

Comprehensive vocabulary flashcards covering the historical development of the periodic table, periodic laws, atomic and ionic radii, ionization energy, electron gain enthalpy, electronegativity, and periodic chemical trends from Class 11 Chemistry Chapter 3.

Dobereiner's Triads

Groups of three elements identified in 1829 with comparable chemical characteristics, arranged in order of increasing atomic weights such that the atomic weight of the middle element was approximately equal to the arithmetic mean of the other two.

Newlands' Law of Octaves

A classification proposed by John Alexander Newlands in 1865 stating that when lighter elements are placed in order of increasing atomic weights, the properties of every eighth element are comparable to those of the first, analogous to notes on a musical scale.

Lothar Meyer's Curve

A graphical representation of atomic volume plotted against atomic mass illustrating that the atomic masses of elements are periodic functions of their physical properties, where elements with similar chemical properties occupy corresponding positions on the curve.

Mendeleev's Periodic Law

The law stating that the properties of elements are periodic functions of their atomic weights, arranging elements in horizontal rows and vertical columns so that elements with comparable properties share the same vertical column.

Modern Periodic Law

The law established following Henry Moseley's 1913 X-ray spectral experiments stating that the physical and chemical properties of elements are periodic functions of their atomic numbers ($Z$).

Covalent Radius

Half the distance between the nuclei of two identical atoms linked by a single covalent bond in a molecule, expressed as $r_A = \frac{d_{A-A}}{2}$.

van der Waals' Radius

Half of the internuclear distance between adjacent atoms of two neighbouring molecules in the solid state.

Metallic Radius

Half the distance between the nuclei of two neighbouring metal atoms in a metallic crystal lattice, expressed as $r_A = \frac{d}{2}$.

Isoelectronic Species

Atoms or ions that possess the same number of electrons (such as $O^{2-}$, $F^{-}$, $Na^{+}$, and $Mg^{2+}$, which each contain 10 electrons) whose sizes decrease with increasing positive nuclear charge.

Ionization Energy

The least amount of energy required to remove an electron from the outermost orbit of an isolated atom in the gaseous state.

Electron Volt (eV)

The energy gained by an electron while travelling under an electric potential difference of one volt, equivalent to $1.602 \times 10^{-19}\,J\,\text{per atom}$ or $96.49\,kJ\,mol^{-1}$.

Electron Gain Enthalpy

The enthalpy change occurring when an electron is added to an isolated neutral gaseous atom to form an anion ($X(g) + e^{-} \rightarrow X^{-}(g)$).

Electronegativity

An atom's tendency to draw the shared pair of electrons towards itself in a covalent bond.

Mulliken Electronegativity

A quantitative electronegativity scale defined as the arithmetic mean of the ionization potential and electron affinity: $\text{Electronegativity} = \frac{\text{IP} + \text{EA}}{2}$.

Diagonal Relationship

The resemblance in chemical and physical characteristics between certain elements of the second period and elements situated diagonally adjacent to them in the third period (such as $Li$ with $Mg$, $Be$ with $Al$, and $B$ with $Si$).

Amphoteric Oxide

An oxide that displays both acidic and basic behaviors, behaving as an acid toward bases and as a base toward acids (such as $Al_2O_3$ and $As_2O_3$).

Neutral Oxide

A non-metallic oxide that exhibits neither acidic nor basic characteristics (such as $CO$, $NO$, and $N_2O$).

Inert Pair Effect

The declining tendency of valence shell $s$-electrons to participate in chemical bonding in heavier elements of groups 13 to 16, resulting in increased stability of lower oxidation states.

Periodicity

The recurrence of identical physical and chemical properties of elements at regular atomic number intervals (magic numbers 2, 8, 8, 18, 18, and 32), caused by repeating configurations of valence shell electrons.

Magic Numbers

The specific atomic number intervals (2, 8, 8, 18, 18, and 32) after which elements exhibit repetitive valence shell electronic configurations and related chemical behaviors.

Pnicogens

The specific family name given to the elements belonging to Group 15 (Group V A) of the periodic table.

Chalcogens

The specific family name given to the elements belonging to Group 16 (Group VI A) of the periodic table.

Transuranic Elements

Synthetic, radioactive elements that possess atomic numbers greater than uranium ($Z > 92$), including the trans-actinide super-heavy elements ($Z = 104\text{--}112$, 114, and 116).