Potassium (K)

Element 19 · alkali metal · group 1, period 4

Electron shells, 2 + 8 + 8 + 1. The outer shell is highlighted - it is the only one that takes part in bonding.

Potassium is element 19, a alkali metal in group 1 and period 4. Its electron configuration is [Ar] 4s1. That leaves 1 valence electron in the outer shell, with the shells filling 2, 8, 8, 1. Losing its 1 valence electron is the shorter route to a full shell, so it carries a charge of +1.

19 protons
1 valence e−
+1
s-block

Properties

Atomic number	19
Symbol	K
Standard atomic weight	39.098 u
Group	1
Period	4
Block	s-block
Category	alkali metal
Electron configuration	1s² 2s² 2p⁶ 3s² 3p⁶ 4s¹
Noble-gas notation	[Ar] 4s¹
Electrons per shell	2, 8, 8, 1
Valence electrons	1
Common ionic charge	+1
Electronegativity (Pauling)	0.82
Protons / electrons	19 / 19

Electron configuration of potassium

Orbitals fill from the lowest energy upward. Writing that out for potassium gives 1s² 2s² 2p⁶ 3s² 3p⁶ 4s¹, which is 1s2 2s2 2p6 3s2 3p6 4s1 in plain text.

Everything up to Ar is the same as in that noble gas, so it is usually abbreviated to [Ar] 4s¹. The part outside the bracket is what does the chemistry.

Subshell	Electrons	Capacity
1s	2	2
2s	2	2
2p	6	6
3s	2	2
3p	6	6
4s	1	2

Potassium ion charge

Potassium commonly forms ions with a charge of +1.

It has 1 valence electron, so it is 7 short of a full octet and 1 above an empty outer shell. An atom takes whichever route is shorter, which is why the charge comes out as it does.

Common questions

How many valence electrons does potassium have?

Potassium has 1 valence electron. For groups 1 and 2 the count is the group number, and potassium is in group 1.

What is the electron configuration of potassium?

1s2 2s2 2p6 3s2 3p6 4s1, or [Ar] 4s1 written from the previous noble gas. Orbitals fill lowest energy first.

What is the charge of potassium?

Potassium commonly forms ions with a charge of +1. With 1 valence electron it is 7 short of an octet and 1 above an empty shell, so it takes whichever route is shorter.

How many protons, electrons and neutrons does potassium have?

A neutral potassium atom has 19 protons and 19 electrons. Its standard atomic weight is 39.098, so the most common isotope has about 20 neutrons.

See the ionic charge of every element →

How this page was produced. The configuration was built by filling orbitals in energy order from atomic number 19 alone, not looked up. The shell counts, the valence count and the charge all follow from it. Nothing on this page is written per element.