Page 4 - Curriculum Visions Dynamic Book

Potassium (K)
Element 19. Potassium, a soft, silvery-white, reactive metal, is an element in group 1 (the alkali metals) in the Periodic Table.
Potassium is the seventh most common element on Earth and makes up 1.5% by weight of the Earth’s crust. It is found in all living matter.
The pure metal, however, has little direct use.
Potassium is a very reactive metal and is never found in its native state, but always as a compound. It is the least dense metal apart from lithium. It is a very soft metal that can be cut with a knife. For a
few moments it is silvery in colour,
but the surface quickly oxidises. Potassium metal is normally kept
under oil to prevent reaction with
air. Potassium reacts so violently
with water that it starts to burn.
When the element burns, it produces
a lilac-coloured flame. Potassium alloys with sodium, making an alloy that is liquid at room temperature.
Key facts...
Name: potassium
Symbol: K, from the Latin kalium Atomic number: 19
Atomic weight: 39.1
Position in Periodic Table: group 1 (1)
(alkali metal); period 4
State at room temperature: solid Colour: silvery-white
Density of solid: 0.86 g/cc
Melting point: 63.38°C
Boiling point: 759°C
Origin of name: a combination of the
English word potash and the Arabic
word qali, meaning alkali
Shell pattern of electrons: 2–8–8–1
Discovery
Potassium was isolated in 1807 by Sir Humphry Davy, who obtained it through the electrolysis of potassium hydroxide (KOH). It was the first metal he isolated by electrolysis. Potassium was collected
at the cathode.
Technology
One of the earliest uses for potassium compounds was in soap. Potassium carbonate was obtained from wood ash
 Potassium salts were traditionally obtained from the ashes of trees and other plants.The ash
yields potassium carbonate contaminated with a
wide variety of other compounds. Potassium is now recovered from coastal salt beds at the same time as brine and also from underground rock deposits.
4