Meaning & use
K
Last updated
Meanings
abbreviationchemistry
The chemical symbol for potassium, the element with atomic number 19.
Grammar: Used in chemical formulas and tables: K, K+, KCl.
Patterns
- K in a formula
- K+ ion
In the periodic table, K stands for potassium.
Bananas are often mentioned as a source of K in the diet.
The compound contains one atom of K and one atom of Cl.
abbreviationphysics
The symbol for kelvin, the SI unit of thermodynamic temperature.
Grammar: Written after a number: 300 K. No degree sign is used.
Patterns
- number + K
The temperature of the liquid was about 300 K.
Absolute zero is defined as 0 K.
The experiment was carried out at 77 K.
abbreviationinformal
An informal written abbreviation for thousand, especially in money amounts or counts.
Grammar: Common in informal writing and online: 10K = 10,000.
Patterns
- number + K
She earns about 50K a year.
The video has over 2 million views and 10K likes.
The race is a 5K, so it is suitable for beginners.
Common combinations
- K+ ion
- Potassium forms a K+ ion in many compounds.
- K in the periodic table
- Students learn that K in the periodic table comes from kalium.
- 300 K
- The gas was cooled to 300 K.
- 50K a year
- The job pays around 50K a year.
Synonyms and how they differ
- potassium
- The English name of the element; K is the symbol used in formulas and tables.
- kelvin
- The unit name; K is the symbol written after a number.
Commonly confused: K or K? K or Ka?
K vs K
The same letter can mean potassium in chemistry, kelvin in physics, or thousand informally; the context tells you which.
K vs Ka
Ka is an acid dissociation constant in chemistry, not the symbol for potassium.
Practice
In a chemistry textbook, what does K most commonly represent?
Choose one answer.
In chemistry, K is the symbol for potassium, from Latin kalium. Kilogram is kg, kelvin is also K but belongs to physics, and 'thousand' is an informal use outside science.
Make it your own
Write a sentence using “K”, then check it and compare it with the examples above.