All practice pages/Interatomic theory/Elements
Element 19, an alkali metal
A soft metal that bursts into lilac flame on water, and an ion every nerve and muscle cell in your body depends on.
Period 4, group 1. The other alkali metals are tinted, and every cell opens its own article.
Potassium has 19 electrons, one for every proton, so the atom carries no charge. Below are the same 19 electrons written two ways.
1s² 2s² 2p⁶ 3s² 3p⁶ 4s¹
Short form: [Ar] 4s¹, where [Ar] stands for the 18 electrons argon already has.
The simple form counts electrons shell by shell. The orbital form says which subshell each one sits in: s holds 2, p holds 6, d holds 10 and f holds 14. Shell 2 here is 2s² 2p⁶, and 2 + 6 is 8.
Potassium sits in period 4 and has 4 shells. The period number counts the shells.
The outer shell holds 1 electron. Those are the ones potassium can lose, gain or share, so they are the ones that decide what it bonds with. For a main-group element the group number gives that count: group 1 means 1.
One valence electron, which potassium gives up easily to form the K⁺ ion. Like the other alkali metals, it reacts with water.
About 2% of the crust by mass, in feldspar and mica. It is mined as potash from beds of salts such as sylvite (KCl) left by ancient seas; the largest deposits are in Saskatchewan, Canada. Bananas, potatoes and beans are rich in it.
Humphry Davy isolated it in 1807 by passing electricity through molten potassium hydroxide, the first metal ever isolated that way; the tiny globules burst into flame. The name comes from potash, the ash of plants soaked in pots. The symbol K comes from kalium, from the Arabic al-qali, plant ashes.
About 95% of potash goes into fertilizer. Potassium compounds also make soap (potassium hydroxide), glass, gunpowder and fireworks (potassium nitrate), salt substitutes (potassium chloride) and potassium iodide tablets for radiation emergencies.
Reacts with water even more violently than sodium, igniting the hydrogen it releases, so it is stored under oil. Old potassium can grow a crust of superoxide that explodes when cut.