Chemical element · reference page

Potassium

Potassium is element 19 (K), located in period 4, group 1 and the s block. At room temperature its reference phase is solid. Its electron configuration is [Ar] 4s1.

Atomic number19

Standard atomic weight39.0983(1)

Group1

Period4

Blocks

Electron configuration[Ar] 4s1

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 potassium 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 potassium 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 0.890g/cm³. The melting point is 336.8 K (63.7 °C). The boiling point is 1 032 K (758.9 °C). Pressure, purity and crystal structure can shift measured physical properties.

Occurrence and applications

Where potassium is found and used

In practice, potassium is encountered in fertiliser production, biology, soaps and chemical bases.

In practice

Examples of real uses

Fertiliser production

Potassium is part of fertiliser chemistry or the industrial processes used to supply essential plant nutrients.

Biology

Potassium ions or compounds participate in biological structures, enzymes, signalling or metabolism.

Soaps

Strong sodium or potassium bases react with fats to produce soap salts in saponification.

Chemical bases

Strong bases or basic compounds of the element are important reagents in industrial and laboratory chemistry.

Periodic position

What its neighbours tell us

Potassium is in period 4 and group 1. In the neighbourhood shown here, calcium is immediately to its right in the same period; sodium is above it and rubidium 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 · 8 · 1

Density0.890g/cm³

Melting point336.8 K (63.7 °C)

Boiling point1 032 K (758.9 °C)

Pauling electronegativity0.82

First ionisation energy418.8 kJ/mol

Electron affinity48.38 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 potassium 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 39.0983(1). This value refers to the isotopic composition of natural terrestrial material, not to the mass of one specific atom.

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