Main-group element

A chemical element in groups 1, 2, or 13–18 of the periodic table, whose valence electrons occupy s or p orbitals.

Periodic table: A tabular arrangement of chemical elements ordered by atomic number and recurring chemical properties. Its group structure defines the main-group elements’ place among all elements.
Octet rule: The heuristic that atoms often gain, lose, or share electrons to reach eight valence electrons. It summarizes bonding patterns common among many p-block elements.
Silicon: A metalloid element with symbol Si and atomic number 14, widely used in semiconductors and glass. Its semiconductor applications illustrate the technological reach of a p-block element.
Transition metal: An element whose atom has a partially filled d subshell or forms cations with an incomplete d subshell. Transition metals occupy the d-block rather than the main-group columns.
Dmitri Mendeleev: A Russian chemist who formulated a periodic table and predicted properties of then-undiscovered elements. His periodic classification established the recurring patterns later used to distinguish element families.
s-block: The region of the periodic table in which the highest-energy electrons occupy an s orbital. Groups 1 and 2 form the s-block portion of the main group.
Ionic bond: An electrostatic attraction between oppositely charged ions formed through electron transfer or redistribution. Alkali and alkaline-earth metals often form cations that bond ionically with nonmetals.
Carbon: A nonmetallic element with symbol C and atomic number 6, capable of forming diverse stable bonds. Its bonding versatility underlies organic molecules and many materials.
Inner transition metal: An element in the f-block, comprising the lanthanide and actinide series. These f-block elements are excluded from the standard main-group definition.
Henry Moseley: An English physicist whose X-ray measurements established atomic number as the basis for ordering elements. Atomic-number ordering clarified the modern group positions that define the main group.

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