Periodic Classification of Elements and Periodicity

This flashcard set covers the fundamental concepts, historical background, and periodic trends of elements as described in the chemistry lecture notes.

Triads

A classification system proposed by Dobereiner in 1829 where elements were arranged in groups of three with similar properties.

Law of Octaves

A principle proposed by Newland in 1864 stating that when elements are arranged by increasing atomic mass, every eighth element has common properties with the first.

Modern Periodic Law

The law stating that if elements are arranged in ascending order of their atomic numbers, their chemical properties repeat in a periodic manner.

Groups

The vertical columns in the periodic table, usually numbered I to VIII, containing elements with similar chemical properties.

Periods

The seven horizontal rows of the periodic table, numbered 1 to 7 using Arabic numerals.

Transition Elements

Less typical elements located in the B subgroups in the center of the periodic table, characterized by partially filled d or f subshells.

Lanthanide Contraction

The gradual reduction in the size of atoms in the Lanthanide series (Period 6) due to the involvement of f-subshells.

Ionization Energy

The minimum energy required to remove an electron from the outermost shell of an isolated gaseous atom in its ground state, measured in kJ\,mol^{-1}.

Shielding Effect

The repulsion caused by inner-shell electrons that reduces the effective nuclear attraction on the outermost electrons.

Electron Affinity

The energy released or absorbed when an electron is added to a gaseous atom to form a negative ion.

Metalloids

Elements that possess properties of both metals and non-metals, such as Silicon (Si), Arsenic (As), and Tellurium (Te).

Oxidation State

The apparent charge (with sign) that an atom would carry in a compound, which is zero in its free state.

Hydration Energy

The heat absorbed or evolved when one mole of gaseous ions dissolves in water to give an infinitely dilute solution.

Amphoteric Oxides

Oxides that show both acidic and basic properties, reacting with both strong acids and strong bases (e.g., ZnO, Al_2O_3).

Alkali Metals

The elements in Group IA (excluding hydrogen) which are highly reactive and form strong alkalies with water.

Alkaline Earth Metals

The elements in Group IIA, named for their presence in the Earth's crust and their alkaline character.

Halogens

The elements in Group VIIA, named for their "salt-forming" properties.

Noble Gases

The least reactive gaseous elements found in Group VIIIA, characterized by complete outermost shells.

Isostere/Isoelectronic

Species (atoms or ions) that have the same number of electrons, such as the series of ions in a period that show decreasing radii from left to right.

Catenation

The ability of an atom (notably Carbon) to form long chains or rings by linking with other atoms of the same element.