Potassium

Potassium, ₀₀K

Potassium pearls (in paraffin oil, ~5 mm each)
Potassium
Appearance	silvery gray
Standard atomic weight Ar°(K)
	39.0983(1)
Potassium in the periodic table
Hydrogen Helium Lithium Beryllium Boron Carbon Nitrogen Oxygen Fluorine Neon Sodium Magnesium Aluminium Silicon Phosphorus Sulfur Chlorine Argon Potassium Calcium Scandium Titanium Vanadium Chromium Manganese Iron Cobalt Nickel Copper Zinc Gallium Germanium Arsenic Selenium Bromine Krypton Rubidium Strontium Yttrium Zirconium Niobium Molybdenum Technetium Ruthenium Rhodium Palladium Silver Cadmium Indium Tin Antimony Tellurium Iodine Xenon Caesium Barium Lanthanum Cerium Praseodymium Neodymium Promethium Samarium Europium Gadolinium Terbium Dysprosium Holmium Erbium Thulium Ytterbium Lutetium Hafnium Tantalum Tungsten Rhenium Osmium Iridium Platinum Gold Mercury (element) Thallium Lead Bismuth Polonium Astatine Radon Francium Radium Actinium Thorium Protactinium Uranium Neptunium Plutonium Americium Curium Berkelium Californium Einsteinium Fermium Mendelevium Nobelium Lawrencium Rutherfordium Dubnium Seaborgium Bohrium Hassium Meitnerium Darmstadtium Roentgenium Copernicium Nihonium Flerovium Moscovium Livermorium Tennessine Oganesson Na ↑ K ↓ Rb argon ← potassium → calcium
Group	group 1: hydrogen and alkali metals
Period	period 4
Block	s-block
Electron configuration	[Ar] 4s1
Electrons per shell	2, 8, 8, 1
Physical properties
Phase at STP	solid
Melting point	336.7 K ​(63.5 °C, ​146.3 °F)
Boiling point	1032 K ​(759 °C, ​1398 °F)
Density (near r.t.)	0.862 g/cm3
when liquid (at m.p.)	0.828 g/cm3
Critical point	2223 K, 16 MPa
Heat of fusion	2.33 kJ/mol
Heat of vaporization	76.9 kJ/mol
Molar heat capacity	29.6 J/(mol·K)
Atomic properties
Oxidation states	−1, +1 (a strongly basic oxide)
Electronegativity	Pauling scale: 0.82
Ionization energies	1st: 418.8 kJ/mol 2nd: 3052 kJ/mol 3rd: 4420 kJ/mol (more)
Atomic radius	empirical: 227 pm
Covalent radius	203±12 pm
Van der Waals radius	275 pm
Spectral lines of potassium
Other properties
Natural occurrence	primordial
Crystal structure	​body-centered cubic (bcc)
Speed of sound thin rod	2000 m/s (at 20 °C)
Thermal expansion	83.3 µm/(m⋅K) (at 25 °C)
Thermal conductivity	102.5 W/(m⋅K)
Electrical resistivity	72 nΩおめが⋅m (at 20 °C)
Magnetic ordering	paramagnetic
Molar magnetic susceptibility	+20.8·10−6 cm3/mol (298 K)
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 Number	7440-09-7
History
Discovery and first isolation	Humphry Davy (1807)
Symbol	"K": from New Latin kalium
Isotopes of potassium
Main isotopes Decay abun­dance half-life (t1/2) mode pro­duct 39K 93.3% stable 40K 0.0120% 1.248×109 y βべーた− 40Ca εいぷしろん 40Ar βべーた+ 40Ar 41K 6.73% stable

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. The unstable isotope with 21 neutrons is one of the most common radioactive materials.

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. The pink or lilac flame comes from 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.

• Chrome alum
• Potash alum
• Potassium arsenate, oxidizing agent, toxic
• Potassium arsenite, colorless solid, toxic
• Potassium bromate, colorless, oxidizing agent, used in flour
• Potassium bromide, colorless, used as sedative
• Potassium carbonate, colorless, reacts with acids
• Potassium chlorate, used in matches and explosives
• Potassium chloride, salt substitute
• Potassium chromate, yellow solid, oxidizing agent, toxic
• Potassium dichromate, red solid, oxidizing agent, toxic
• Potassium fluoride, used to make fluorine, corrosive
• Potassium hydroxide, also known as potash, caustic, strong base, white solid
• Potassium hypomanganate, bright blue hypomanganate, rare
• Potassium iodate, used to supply iodine
• Potassium iodide, used to supply iodine
• Potassium manganate, used to make potassium permanganate
• Potassium nitrate, used in gunpowder
• Potassium perchlorate, used in some rockets
• Potassium periodate
• Potassium permanganate, purple, disinfectant, oxidizing agent
• Potassium sulfide, reacts with water
• Potassium sulfite, used in food preservation
• Potassium sulfate, colorless, used in fertilizers

• 
  Potassium hydroxide
• 
  Potassium chlorate
• 
  Potassium chloride
• 
  Potassium chromate

Name

The word potassium comes from the word "potash". Potash is a mixture of potassium carbonate and potassium hydroxide that has been used for a very long time. In past centuries potash was made from ashes in pots. It is used to make fertilizer, soap, and glass.

Occurrence

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.

Uses

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

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

Nutrition

Potassium ions are very important to organisms. That is why fertilizers have potassium compounds in them. The ions 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. Potassium compounds are not normally dangerous, unless they contain a toxic anion like chromate or chlorate.

Related pages

• Lithium
• Rubidium
• Caesium
• Alkali metal

Other websites

• Potassium -Citizendium