Potassium (K)

Potassium properties

Atomic number

19

Atomic mass

39.098 u

Category

Alkali metal

Group

1

Period

4

Block

s-block

State at room temp.

Solid

Electronegativity

0.82

Melting point

336.7 K (63.6 °C)

Boiling point

1,032 K (758.8 °C)

Density

0.862 g/cm³

Valence electrons

1

Common charges

+1

Oxidation states

+1

Atomic radius

275 pm

Ionization energy

4.341 eV

Electron affinity

0.501 eV

Radioactive

No, has stable isotopes

Discovered

1807

Potassium electron configuration

The electron configuration of Potassium (K) is [Ar] 4s1. Its 19 electrons are arranged in shells as 2, 8, 8, 1.

Protons, neutrons and electrons in Potassium

A neutral Potassium atom has 19 protons and 19 electrons. Most Potassium atoms have about 20 neutrons: the atomic mass rounded to 39, minus the atomic number 19.

Neutrons are approximate: atoms of the same element can have different numbers of neutrons (isotopes). Atomic number and mass

How many valence electrons does Potassium have?

1

Potassium has 1 valence electron in its outermost shell, shell 4. These are the electrons involved in chemical bonding.

See every element: Periodic table with valence electrons

Potassium orbital diagram

Each box is an orbital that holds up to two electrons with opposite spins (↑↓). The inner shells are the same as the noble gas in brackets. How to write electron configurations

Molar mass of Potassium

39.098 g/mol

One mole of Potassium atoms (6.022 × 10²³ atoms) has a mass of 39.098 grams. Use this value to convert between grams and moles.

Compounds containing Potassium

Potassium facts

• Potassium's symbol, K, comes from its Latin name kalium, based on 'kali', an old word for alkali.
• A tiny fraction of natural potassium is radioactive potassium-40, so potassium-rich foods such as bananas are very slightly radioactive.
• Potassium (K) has atomic number 19 and is a solid at room temperature. It was discovered in 1807.

Position in the periodic table

Potassium is element 19, in period 4 and group 1 of the periodic table, in the s-block.

All alkali metals

Uses of Potassium

Potassium is used mainly in fertilizers, as potash (potassium chloride), because plants need it in large amounts. Potassium nitrate is an ingredient of gunpowder and fireworks, and potassium hydroxide is used to make soft soaps and as the electrolyte in alkaline batteries. Potassium chloride also serves as a low-sodium salt substitute.

Who discovered Potassium?

Humphry Davy isolated potassium in 1807 at the Royal Institution in London, by passing an electric current through molten potash (potassium hydroxide). It was the first metal ever isolated by electrolysis.

Where does the name come from?

Humphry Davy named potassium in 1807 after potash, literally 'pot ash', made by soaking plant ashes and boiling down the liquid in pots. The symbol K comes from the New Latin kalium, from the Arabic qali, 'plant ashes'.

Discovery timeline