Potassium

argon ← potassium → calcium Na ↑ K ↓ Rb 19K Periodic table
Appearance
silvery gray Potassium pearls under paraffin oil. The large pearl measures 0.5 cm. Below: spectral lines of potassium
General properties
Name, symbol, number	potassium, K, 19
Pronunciation	/pɵˈtæsiəm/ po-TAS-ee-əm
Element category	alkali metal
Group, period, block	1, 4, s
Standard atomic weight	39.0983(1) g·mol−1
Electron configuration	[Ar] 4s1
Electrons per shell	2, 8, 8, 1 (Image)
Physical properties
Phase	solid
Density (near r.t.)	0.862 g·cm−3
Liquid density at m.p.	0.828 g·cm−3
Melting point	336.53 K, 63.38 °C, 146.08 °F
Boiling point	1032 K, 759 °C, 1398 °F
Triple point	336.35 K (63°C),  kPa
Heat of fusion	2.33 kJ·mol−1
Heat of vaporization	76.9 kJ·mol−1
Specific heat capacity	(25 °C) 29.6 J·mol−1·K−1
Atomic properties
Oxidation states	1 (strongly basic oxide)
Electronegativity	0.82 (Pauling scale)
Ionization energies	1st: 418.8 kJ·mol−1
	2nd: 3052 kJ·mol−1
	3rd: 4420 kJ·mol−1
Atomic radius	227 pm
Covalent radius	203±12 pm
Van der Waals radius	275 pm
Miscellanea
Crystal structure	body-centered cubic
Magnetic ordering	paramagnetic
Electrical resistivity	(20 °C) 72 nΩ·m
Thermal conductivity	(300 K) 102.5 W·m−1·K−1
Thermal expansion	(25 °C) 83.3 µm·m−1·K−1
Speed of sound (thin rod)	(20 °C) 2000 m/s
Young's modulus	3.53 GPa
Shear modulus	1.3 GPa
Bulk modulus	3.1 GPa
Mohs hardness	0.4
Brinell hardness	0.363 MPa
CAS registry number	7440-09-7
Most stable isotopes
Main article: Isotopes of potassium
iso NA half-life DM DE (MeV) DP 39K 93.26% 39K is stable with 20 neutrons 40K 0.012% 1.248(3)×109 y β− 1.311 40Ca ε 1.505 40Ar β+ 1.505 40Ar 41K 6.73% 41K is stable with 22 neutrons

Potassium metal

Potassium is a chemical element in the periodic table. It has the symbol K. This symbol is taken from the Latin word kalium. Potassium's atomic number is 19. It has 19 protons and electrons. Potassium is not found as an element in nature, because it is so reactive.

Potassium has two stable isotopes, with 20 or 22 neutrons. Its atomic mass is 39.098.

Properties

Physical properties

Potassium is a soft gray metal. It can be cut easily with a knife. Its melting point is 63 degrees celsius (145.4 degrees Fahrenheit). It melts at a very low temperature. It is an alkali metal. It is the second lightest metal, after lithium.

Chemical properties

A reaction of potassium metal with water. Hydrogen is liberated that burns with a pink or lilac flame, the flame color owing to burning potassium vapor. Strongly alkaline potassium hydroxide is formed in solution.

Potassium reacts in many chemical reactions similar to sodium and other alkali metals. It tarnishes in air to produce a whitish oxidized layer on the surface. This is why it is stored in oil. It also reacts very fast with water, which is another reason for its storage in oil. The hydrogen produced during its reaction with water can burst into flames when a large amount of potassium is added to water. Potassium hydroxide is also produced. Potassium also burns in air easily, to make the peroxide or the superoxide.

Chemical compounds

Potassium chloride in a flame

Potassium compounds are only in one oxidation state: +1. Potassium ions are colorless and similar to sodium ions. Potassium chloride can be used as a substitute for table salt. Potassium hydroxide is used in the electrolyte of alkaline cells. Most potassium compounds are nontoxic. If they are toxic, it is because of the anion. Potassium chromate is colored because of the chromate, not the potassium. Potassium chromate is toxic because of the chromate, not the potassium.

• 

  Potassium hydroxide

• 

  Potassium chlorate

• 

  Potassium chloride

• 

  Potassium chromate

Name

The word potassium comes from the word "potash". Potash is a chemical that is a mixture of potassium carbonate and potassium hydroxide that has been used for a very long time. It is used to make fertilizer, soap, and glass.

Occurrence

Sylvite, a natural potassium chloride mineral

Potassium does not occur in nature because it is too reactive. It is found in minerals, though. It is extracted from them by electrolysis of potassium hydroxide or potassium chloride. The potassium hydroxide or potassium chloride has to be melted at a very high temperature.

Use as element

It is used to absorb water from solvents. It is also used in some scientific instruments.

Use as compounds

Potassium compounds are used in soap, fertilizer, explosives, and matches.

Use by living organisms

Potassium ions are very important to organisms. They send messages from cells to other cells. It helps biological membranes depolarize. This means go from a negative to a positive electrical charge. This is needed for muscles to contract (get shorter and move things.) It is needed for the heart to beat (push blood through blood vessels.) If the potassium level in the blood is too high or too low it can cause death because the heart stops. A few good sources of potassium are bananas, apricots and raisins.

Safety

Potassium metal is very dangerous and can form an explosive coating if it is kept in air. It also reacts violently with water, spewing corrosive liquid all over. Potassium compounds are not normally dangerous, unless they contain a toxic anion like chromate or chlorate.

Related pages

• Lithium
• Rubidium
• Caesium
• Alkali metal