Potassium (K)
Potassium is the 19th element, a alkali metal in the s-block. Its standard atomic weight is 39.098.
Potassium
39.098
What the table records
- Atomic number
- 19
- Standard atomic weight
- 39.098
- Group
- 1
- Period
- 4
- Block
- s-block
- Category
- Alkali metal
- [Ar] 4s1
- Valence electrons
- 1
- Typical valence
- 1
- Van der Waals radius
- 2.8 Å
- Covalent radius
- 2.03 Å
Molecules containing potassium
The lightest named structures in this library that contain K.
Potassium
K · 39.1 g/mol
Potassium Cation
K+ · 39.1 g/mol
Potassium Hydroxide
HKO · 56.11 g/mol
CID 101459920
CKN · 65.12 g/mol
potassium methanolate
CH₃KO · 70.13 g/mol
potassium cyanate
CKNO · 81.12 g/mol
potassium acetate
C₂H₃KO₂ · 98.14 g/mol
CID 14574551
CKO₃- · 99.11 g/mol
carbonic acid, potassium salt
CH₂KO₃ · 101.12 g/mol
potassium 2-methylpropan-2-olate
C₄H₉KO · 112.21 g/mol
Potassium tert-butoxide
C₄H₁₀KO · 113.22 g/mol
potassium 2-methylbutan-2-olate
C₅H₁₁KO · 126.24 g/mol
How to read these numbers
The standard atomic weight is an average over the isotopes as they occur naturally, which is why it is rarely a whole number. It is the figure a molar mass calculation uses. Work in mass spectrometry wants the monoisotopic mass of a single isotope instead, which is a different number.
The two radii are not the same measurement. The covalent radius is half the distance between two bonded atoms of the element; the van der Waals radius is how close a non-bonded atom gets before repulsion takes over, and is always the larger. Space-filling models are drawn with the second, ball-and-stick models with the first — which is why the same molecule looks so different in the two.