Potassium (K)
Potassium is element 19, an alkali metal in group 1, period 4. A neutral atom has 19 protons, 20 neutrons and 19 electrons, 1 of them valence electrons.
Alkali metal- Atomic number
- 19
- Atomic mass
- 39.098 u
- Valence electrons
- 1
- Protons · neutrons
- 19 · 20
- Electrons per shell
- 2, 8, 8, 1
- At room temperature
- solid
Bohr model of potassium
The Bohr model draws potassium as a nucleus of 19 protons and 20 neutrons, with its 19 electrons on 4 circular shells: 2 in shell 1, 8 in shell 2, 8 in shell 3, 1 in shell 4. Press Build the atom to watch the shells fill from the inside out. The outer ring (the N shell) is dashed: the electrons there are the ones that take part in chemistry.
Real electrons don't travel in neat circles. They live in fuzzy orbitals, shown below, but the Bohr picture is the quickest way to count shells and valence electrons.
Electron configuration of potassium
1s² 2s² 2p⁶ 3s² 3p⁶ 4s¹
Short form (noble gas notation): [Ar] 4s¹. The [Ar] stands for the electrons of argon, the noble gas before it.
How many valence electrons does potassium have?
Potassium has 1 valence electron.
Potassium is in group 1, so it has 1 valence electron. It tends to lose that electron and form a +1 ion.
Protons, neutrons and electrons
| Protons | 19 | equal to the atomic number |
|---|---|---|
| Electrons | 19 | equal to the protons in a neutral atom |
| Neutrons | 20 | mass number 39 − 19 protons |
Atoms of the same element can have different numbers of neutrons (isotopes). The count above uses the rounded atomic mass, the way it's taught in class.
Potassium properties
| Symbol | K |
|---|---|
| Category | Alkali metal |
| Group · period · block | 1 · 4 · s |
| Atomic mass | 39.098 u |
| State at 25 °C | solid |
| Melting point | 336.5 K (63.4 °C, 146 °F) |
| Boiling point | 1,032 K (759 °C, 1,400 °F) |
| Density | 0.89 g/cm³ |
| Electronegativity (Pauling) | 0.82 |
| Atomic radius | 275 pm |
| First ionization energy | 4.341 eV |
| Electron affinity | 0.501 eV |
| Oxidation states | +1 |
| Common ion charge | +1 |
| Discovered | 1807 by Humphry Davy |
Where potassium sits on the periodic table
Group 1: Hydrogen, Lithium, Sodium, Rubidium, Cesium, Francium.
Questions about potassium
How many valence electrons does potassium have?
Potassium has 1 valence electron.
How many protons, neutrons and electrons does potassium have?
A neutral potassium atom has 19 protons and 19 electrons. Its most common form has about 20 neutrons (mass number 39 − 19 protons).
What is the electron configuration of potassium?
1s² 2s² 2p⁶ 3s² 3p⁶ 4s¹, written in short form as [Ar] 4s¹.
What does the Bohr model of potassium look like?
A nucleus of 19 protons and 20 neutrons, circled by 4 electron shells holding 2, 8, 8, 1 electrons.
What is the atomic number of potassium?
19. The atomic number is the number of protons in the nucleus, and it is what makes an atom potassium.