---
title: "Potassium (K): Atomic Mass, Electron Configuration & Properties"
url: https://www.moldraw.com/elements/potassium.html
description: "Potassium (K), element 19: atomic mass 39.098, electron configuration [Ar] 4s¹, group 1, period 4, s-block alkali metal. Melting and boiling point, density, electronegativity and shells."
lang: en
publisher: Scidart Academy
generated: 2026-11-03
---
19K39.098

# Potassium (K) – element 19

Potassium is a chemical element with the symbol **K** and atomic number **19**. It is a alkali metal in group 1 (alkali metals), period 4 of the periodic table (s-block), and is a solid at room temperature.

Potassium (K) has atomic number 19, atomic mass 39.098 u and electron configuration [Ar] 4s1.

[Download periodic table PDF](https://www.moldraw.com/printables/periodic-table.pdf)[Open interactive periodic table](https://www.moldraw.com/tools/free-chem-tools/interactive-periodic-table.html)

## Potassium facts

| Symbol | K |
| --- | --- |
| Atomic number | 19 |
| Atomic mass | 39.098 u (g/mol) |
| Category | alkali metal |
| Group | group 1 (alkali metals) |
| Period | 4 |
| Block | s-block |
| Phase at 20 °C | Solid |
| Electron configuration | 1s2 2s2 2p6 3s2 3p6 4s1 |
| Noble-gas notation | [Ar] 4s1 |
| Electrons per shell | 2, 8, 8, 1 |
| Valence electrons | 1 |

## Bohr model and shells

Potassium has 19 electrons in 4 shells: 2, 8, 8, 1. Full configuration and noble-gas notation are in the table; work out any element or ion with the [electron configuration calculator](https://www.moldraw.com/tools/free-chem-tools/electron-configuration-calculator.html).

## Physical and atomic properties

| Melting point | 336.7 K (63.6 °C) |
| --- | --- |
| Boiling point | 1032 K (758.9 °C) |
| Density | 0.862 g/cm³ |
| Electronegativity (Pauling) | 0.82 |
| Electron affinity | 48.383 kJ/mol |
| Ionization energies | 418.8, 3052, 4420 kJ/mol (1st, 2nd, 3rd) |
| Molar heat capacity | 29.6 J/(mol·K) |
| Discovered by | Humphry Davy |

Use the atomic mass in the [molar mass calculator](https://www.moldraw.com/tools/free-chem-tools/molar-mass-calculator.html) for any formula containing K.

## Position in the periodic table

Tap any element to open its page.

## Frequently asked questions

### What is the atomic mass of potassium?

The atomic mass of potassium is 39.098 u, so one mole of potassium atoms weighs 39.098 g.

### What is the electron configuration of potassium?

Potassium has 19 electrons: 1s² 2s² 2p⁶ 3s² 3p⁶ 4s¹, or [Ar] 4s¹ in noble-gas notation. Electrons per shell: 2, 8, 8, 1.

### How many valence electrons does potassium have?

Potassium has 1 valence electron (group 1).

### Is potassium a metal?

Yes. Potassium is a alkali metal.

### Where is potassium on the periodic table?

Potassium is in group 1 (alkali metals), period 4, in the s-block.

Data: [Periodic-Table-JSON](https://github.com/Bowserinator/Periodic-Table-JSON) (CC BY-SA 3.0); standard atomic weights from IUPAC (abridged). Values in brackets are the mass number of the longest-lived isotope.