Unit 3: Classification of Elements and Periodicity in Properties - Vocabulary Flashcards

Vocabulary flashcards focusing on key concepts, laws, block classifications, and periodic property trends from Unit 3.

Law of Triads

A classification pattern noted by Johann Dobereiner in 1829 stating that in groups of three elements with similar physical and chemical properties, the middle element has an atomic weight approximately halfway between the atomic weights of the other two.

Law of Octaves

A relationship proposed by John Alexander Newlands in 1865 stating that when elements are arranged in increasing order of their atomic weights, every eighth element exhibits properties similar to the first, holding true for elements up to calcium.

Mendeleev's Periodic Law

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

Modern Periodic Law

The law formulated after Henry Moseley's 1913 experiments stating that the physical and chemical properties of the elements are periodic functions of their atomic numbers ($Z$).

Eka-Aluminium and Eka-Silicon

Names given by Dmitri Mendeleev to undiscovered elements predicted to fill gaps under aluminium and silicon, which were later discovered as gallium ($\text{Ga}$) and germanium ($\text{Ge}$) respectively.

Period

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

Group

A vertical column in the Periodic Table containing elements with similar valence shell electronic configurations and chemical properties, numbered 1 through 18 according to IUPAC recommendations.

s-Block Elements

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

p-Block Elements

Elements belonging to Groups 13 to 18 with outermost electronic configurations ranging from $ns^2 np^1$ to $ns^2 np^6$ in each period.

Representative Elements

The elements comprising the s-block and p-block combined, also known as Main Group Elements.

d-Block Elements

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

f-Block Elements

Inner-transition elements comprising the Lanthanoids ($\text{Ce}, Z=58$ to $\text{Lu}, Z=71$) and Actinoids ($\text{Th}, Z=90$ to $\text{Lr}, Z=103$), characterized by outer electronic configuration $(n-2)f^{1-14}(n-1)d^{0-1}ns^2$.

Transuranium Elements

Synthesized, radioactive elements that follow uranium ($Z = 92$) in the Periodic Table.

Metalloids

Elements bordering the thick zig-zag line running diagonally across the Periodic Table (such as silicon, germanium, arsenic, antimony, and tellurium) that exhibit properties characteristic of both metals and non-metals.

Covalent Radius

Half the distance between two atoms bound together by a single bond in a covalent homonuclear molecule, such as $99\,\text{pm}$ for chlorine derived from a bond distance of $198\,\text{pm}$.

Metallic Radius

Half the internuclear distance separating metal cores in a metallic crystal lattice, such as $128\,\text{pm}$ for copper derived from an internuclear distance of $256\,\text{pm}$.

Isoelectronic Species

Atoms and ions that contain the same number of electrons, such as $\text{O}^{2-}$, $\text{F}^-$, $\text{Na}^+$, and $\text{Mg}^{2+}$ which all possess $10\,\text{electrons}$.

Ionization Enthalpy

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

Shielding Effect

The screening of valence electrons from the full nuclear charge by intervening inner core electrons, reducing the effective nuclear charge experienced by the outer electrons.

Electron Gain Enthalpy

The enthalpy change ($\Delta_{eg}H$) accompanying the addition of an electron to a neutral gaseous atom ($\text{X}$) 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.

Pauling Scale

An arbitrarily defined scale developed by Linus Pauling in 1922 to measure electronegativity, assigning fluorine the highest value of $4.0$.

Diagonal Relationship

The similarity in physical and chemical behavior observed between the first element of a group in the second period (e.g., $\text{Li}$, $\text{Be}$) and the second element in the adjacent group of the third period (e.g., $\text{Mg}$, $\text{Al}$).

Amphoteric Oxides

Oxides that exhibit both acidic and basic properties, behaving as acidic with bases and as basic with acids, such as $\text{Al}_2\text{O}_3$ and $\text{As}_2\text{O}_3$.