Classification of Elements and Periodicity in Properties Flashcards

A set of vocabulary flashcards covering the historical development, structural organization, and periodic trends of the chemical elements as described in the lecture notes.

Johann Dobereiner

A German chemist who in the early 1800s was the first to consider trends among properties of elements and identified several groups of three elements called Triads.

Law of Triads

A relationship noted by Dobereiner where the middle element of a triad had an atomic weight about half way between the atomic weights of the other two, and properties in between them.

A.E.B. de Chancourtois

A French geologist who in 1862 arranged known elements in order of increasing atomic weights and created a cylindrical table to display periodic recurrence of properties.

John Alexander Newlands

An English chemist who in 1865 proposed the Law of Octaves, noting that when elements were arranged by increasing atomic weight, every eighth element had properties similar to the first.

Mendeleev’s Periodic Law

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

Modern Periodic Law

The modified principle stating that the physical and chemical properties of the elements are periodic functions of their atomic numbers ($Z$).

Atomic Number ($Z$)

A fundamental property of an element equal to the nuclear charge (number of protons) or the number of electrons in a neutral atom.

Periods

The horizontal rows in the Periodic Table, where the period number corresponds to the highest principal quantum number ($n$) of the elements in that row.

Groups

The vertical columns in the Periodic Table, numbered 1 to 18 according to IUPAC, containing elements with similar outer electronic configurations.

Lanthanoids

The $4f$-inner transition series of elements starting from Cerium ($Z=58$) and ending at Lutetium ($Z=71$).

Actinoids

The $5f$-inner transition series of elements beginning after Actinium ($Z=89$) and including radioactive, often man-made elements.

s-Block Elements

Elements in Group 1 (alkali metals) and Group 2 (alkaline earth metals) with $ns^1$ or $ns^2$ outermost electronic configurations.

p-Block Elements

Elements belonging to Groups 13 to 18 which, together with s-block elements, are called Representative Elements or Main Group Elements.

d-Block Elements (Transition Elements)

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

f-Block Elements (Inner-Transition Elements)

The Lanthanoids and Actinoids located at the bottom of the Periodic Table, characterized by the filling of f-orbitals.

Transuranium Elements

The elements located after Uranium ($Z=92$) in the Periodic Table.

Metalloids (Semi-metals)

Elements bordering the zig-zag line in the Periodic Table (e.g., Silicon, Germanium, Arsenic) that show properties characteristic of both metals and non-metals.

Covalent Radius

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

Metallic Radius

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

Isoelectronic Species

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

Ionization Enthalpy ($\Delta_i H$)

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

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

The enthalpy change that occurs 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, often measured on the Pauling scale.

Diagonal Relationship

The similarity in chemical behavior between certain first-row elements (like Lithium and Beryllium) and the second-row elements of the following group (like Magnesium and Aluminium).

Amphoteric Oxides

Oxides that behave as acidic with bases and as basic with acids, such as $Al_2O_3$ and $As_2O_3$.