Chemical element · reference page

11Na

Sodium

Sodium is element 11 (Na), located in period 3, group 1 and the s block. At room temperature its reference phase is solid. Its electron configuration is [Ne] 3s1.

Atomic number11

Standard atomic weight22.98976928(2)

Group1

Period3

Blocks

Electron configuration[Ne] 3s1

Electronic structure

What controls its chemistry

The outer electron configuration ends in s¹. Losing that single valence electron gives a +1 ion with a filled inner-shell configuration, so sodium compounds are dominated by the +1 oxidation state.

The same outer-shell pattern is shared by the alkali metals. Down the group the outer electron is farther from the nucleus and generally easier to remove, which helps explain the high reactivity of the family.

Chemical forms

Compounds, ions and materials

The dominant chemical form is sodium in the +1 oxidation state. Ionic halides, hydroxides and oxygen-containing salts are common; the free metal is much less common in nature because it reacts readily with water, oxygen and other non-metals.

Physical behaviour

State and phase changes

The reference phase at room temperature is solid. The listed density is 0.968 g/cm³. The melting point is 370.9 K (97.8 °C). The boiling point is 1 156 K (882.9 °C). Pressure, purity and crystal structure can shift measured physical properties.

Occurrence and applications

Where sodium is found and used

In practice, sodium is encountered in common salts, chemical synthesis and reactor coolant.

In practice

Examples of real uses

Common salts

Everyday exposure to sodium is through ionic compounds rather than the free element itself.

Chemical synthesis

Sodium is used as an element, reagent, catalyst component or precursor in the manufacture of other chemicals.

Reactor coolant

Liquid sodium has high thermal conductivity and is used as a coolant in some fast-neutron reactor designs.

Periodic position

What its neighbours tell us

Sodium is in period 3 and group 1. In the neighbourhood shown here, magnesium is immediately to its right in the same period; lithium is above it and potassium below it in the same group. These positions make it possible to compare atomic size, ionisation energy and bonding behaviour with nearby elements.

Reference data

Physical and atomic properties

Classificationalkali metal

Phase at room temperatureSolid

Electron shells2 · 8 · 1

Density0.968 g/cm³

Melting point370.9 K (97.8 °C)

Boiling point1 156 K (882.9 °C)

Pauling electronegativity0.93

First ionisation energy495.8 kJ/mol

Electron affinity52.87 kJ/mol

Values describe the element or neutral atom where applicable. Physical data can depend on allotrope, pressure and measurement conditions.

History

Discovery and identification

The discovery of sodium is associated with Humphry Davy. Recognition of the element, isolation of a pure sample and assignment of its modern atomic number did not necessarily occur at the same time.

Isotopes and atomic weight

How isotope composition changes the numbers

The standard atomic weight is 22.98976928(2). This value refers to the isotopic composition of natural terrestrial material, not to the mass of one specific atom.

Sodium has at least one stable isotope. Different isotopes have the same number of protons and therefore the same element identity, but different neutron numbers and atomic masses.

Safety

Handling and exposure

Elemental sodium reacts readily with moisture and can react violently with water. It is handled away from water and air under controlled conditions.