Period 3 element

A chemical element in the third row of the periodic table, from sodium through argon. The set shows a progression from metallic to nonmetallic properties across the row.

Periodic table: A tabular arrangement of chemical elements ordered by atomic number and organized to reveal recurring properties. Period 3 elements occupy one horizontal row in this broader arrangement.
Effective nuclear charge: The net positive charge experienced by an electron after shielding by other electrons. It generally rises across Period 3, drawing valence electrons closer to the nucleus.
Sodium-vapor lamp: A gas-discharge lamp that produces light by exciting sodium vapor. Sodium’s emission produces the characteristic yellow light used in some street lighting.
Sodium: A soft, highly reactive alkali metal with atomic number 11. It is the most electropositive and metallic member at the row’s left edge.
Electron shell: A set of atomic orbitals grouped by principal quantum number, describing electrons at similar energy levels. Each Period 3 atom has electrons in a third principal shell.
Atomic radius: A measure of the size of an atom, commonly inferred from distances between bonded or neighboring atoms. Its general decrease across the period follows the increasing effective nuclear charge.
Magnesium alloy: A metallic material in which magnesium is the principal element, often valued for low density. Magnesium’s light alloys are used where reducing structural weight matters.
Magnesium: An alkaline-earth metal with atomic number 12 and two valence electrons. Its divalent chemistry contrasts with sodium’s typical formation of singly charged ions.
Valence electron: An electron in an atom’s outermost occupied shell that participates in chemical bonding. The number of outer-shell electrons increases across Period 3 and shapes its chemistry.
First ionization energy: The minimum energy needed to remove one electron from a neutral atom in the gas phase. Its overall rise across the row reflects increasingly strong attraction to outer electrons.

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Period 4 elementCompared with: The preceding period lacks the 3d transition-metal series found in Period 4.