Classification of Elements and Periodicity in Properties

Comprehensive vocabulary flashcards covering the classification of elements, periodic laws, blocks, nomenclature, and trends in chemical properties based on lecture notes.

Triads

Small groups of three elements classified by Johann Dobereiner where the atomic mass of the middle element is approximately the average of the other two.

Law of Octaves

A classification by Newlands stating that when elements are arranged in increasing order of atomic masses, the properties of every eighth element are similar to the first.

Lothar Meyer's Classification

A system where physical properties like atomic volume, melting point, and boiling point were plotted against atomic weight to reveal a periodically repeated pattern.

Mendeleev's Periodic Law

The principle stating that the properties of elements are the periodic functions of their atomic weights.

Eka-Aluminium and Eka-Silicon

Names given by Mendeleev to the then-undiscovered elements Gallium and Germanium, for which he predicted properties and left gaps in his periodic table.

Modern Periodic Law

The principle proposed by Henry Moseley stating that the physical and chemical properties of elements are the periodic functions of their atomic numbers.

Inner Transition Elements

Two rows of 14 elements each (Lanthanoids and Actinoids) placed below the main body of the periodic table.

Lanthanoids

The 14 elements of the sixth period from $57Ce$ to $71Lu$, also known as rare earths.

Actinoids

The 14 elements of the seventh period from $90Th$ to $103Lr$, all of which are radioactive.

Alkali Metals

Group 1 elements with a general outer electronic configuration of $ns^1$.

Alkaline Earth Metals

Group 2 elements with a general outer electronic configuration of $ns^2$.

s-block Elements

Reactive metals in groups 1 and 2 where the last electron enters the outermost s subshell.

p-block Elements

Elements in groups 13 to 18 where the last electron enters the outermost p subshell.

Representative Elements

The collection of s-block and p-block elements together.

Transition Elements (d-block)

Metals in groups 3 to 12 where the last electron enters the penultimate d sub shell, having the general configuration $(n-1)d^{1 \text{ to } 10} ns^{0 \text{ to } 2}$.

Trans-uranium Elements

Artificial elements in the actinide series occurring after Uranium $(Z=92)$.

Covalent Radius

Half of the inter-nuclear distance between two covalently single-bonded atoms, such as $99\,pm$ for the $Cl_2$ molecule.

Van der Waal's Radius

Half of the inter-nuclear distance between two non-bonded atoms of separate molecules in the solid state.

Shielding Effect

The phenomenon where inner electrons partially block the attractive force of the nucleus, causing outer electrons to experience reduced nuclear attraction.

Isoelectronic Species

Atoms and ions that possess the same number of electrons, such as $N^{3-}$, $O^{2-}$, $F^-$, $Ne$, $Na^+$, $Mg^{2+}$, and $Al^{3+}$.

Ionisation Enthalpy ($\Delta_i H$)

The energy required to remove an electron from the outermost shell of an isolated gaseous atom in its ground state.

Electron Gain Enthalpy ($\Delta_{eg} H$)

The enthalpy change occurring when an electron is added to the outermost shell of an isolated gaseous atom.

Electronegativity

The ability of an atom in a compound to attract a shared pair of electrons, measured on scales like the Pauling Scale.

Electropositivity

The tendency of an atom to lose its most loosely bound valence electron, which is directly related to metallic character.

Diagonal Relationship

Similarities in properties between diagonally placed elements of the 2nd and 3rd periods, such as Lithium and Magnesium.

Amphoteric Oxides

Oxides that exhibit both acidic and basic properties, such as $Al_2O_3$ and $As_2O_3$.