Potassium (K)

Potassium is a chemical element with the atomic number 19 in the periodic table of elements. With about 2.0 to 2.5 percent occurrence in the Earth’s crust, it’s the eighth most abundant element found in the layers of our planet. As a member of the alkali metals family in the periodic table, potassium has one valence electron in its outermost shell. 

This extremely reactive chemical is also one of the most essential trace minerals found in the human body, and it’s responsible for some vital processes. Most notably, it’s responsible for the control and regulation of the exchange of electrical impulses in the heart’s cells and within other muscles, as well as the regulation of the fluid balance within the body.

Chemical and Physical Properties of Potassium

Atomic number19
Atomic weight (mass)39.0983 g.mol-1
UsesUsed as potash in making glass & soap. Also as saltpeter, potassium nitrate (KNO3) to make explosives and to color fireworks in mauve. Formerly called kalium (K). Vital to function of nerve and muscle tissues.
DescriptionFairly hard, silvery-white metal. Fifth most abundant element in the earth’s crust (41,500 ppm). Occurs only in compounds.
Group1 (Alkali Metals)
Physical stateA soft metal at room temperature
Half-lifeFrom less than 10 picoseconds to 1.248×109 years
Density0.862 g.cm-3
Melting point336.9°C
Boiling point1038.7°C
Van der Waals radius0.235 nm
Ionic radius1.51 (+1) Å
Most characteristic isotope39K
Electronic shell[Ar] 4s1
The energy of the first ionization418.6 kj.mol-1
Covalent Radius2.03 Å
Atomic Radius2.77 Å
Atomic Volume45.46 cm³/mol
Name OriginEnglish: pot ash; symbol from Latin: kalium, (alkali).
Discovery dateIn 1807 by Sir Humphrey Davy
Oxidation States1

Represented by the symbol K, the chemical element potassium has the atomic number 19, an atomic mass of 39.0983 g.mol-1, and electron configuration [Ar] 4s1. Potassium is a soft, silvery-white metal that reaches its boiling point at 759°C (1398°F or 1032 K), while the melting point is achieved at 63.5°C (146.3°F or 336.7 K).

This alkali element of the periodic table has an electronegativity of 0.8 according to Pauling, whereas the atomic radius according to van der Waals is 0.235 nm. 

As it has a lower density than water, potassium can actually float on it. However, when it comes into contact with H2O (water) molecules, this soft metal reacts violently by releasing hydrogen and emitting a purple flame. In contact with air, the elemental potassium oxidizes and tarnishes very quickly.                         

How Was Potassium Discovered?

Since 500 A.D., people would collect the ashes from burnt wood and wash them in order to obtain potash, also referred to as vegetable alkali. This is a potassium compound called potassium carbonate (K2 CO3), which was used as a cleaning agent. At the time, people were also familiar with another similar substance that they obtained from a specific type of rock with mineral alkali properties. They called it soda ash (sodium carbonate, Na2 CO3). The two substances differed only based on the source they were obtained from. 

Contributions by Sir Humphry Davy

In 1806, the English chemist Sir Humphry Davy attempted to distinguish these two substances by isolating the compounding elements. To that end, Davy attempted electrolysis on both compounds. However, due to the high reactivity of potassium and sodium, the first experiment of the English chemist left no significant results. Namely, although the electric current indeed freed potassium and sodium from the compound, they instantly reacted with the H2O (water) molecules.

Luckily, this didn’t discourage Davy. During his second attempt to separate the elements from the potash and soda ash compounds, he decided to leave out the water. This time, he passed the electric current through molten samples of both compounds, which resulted in a metal droplet formed by each substance – a pure elemental form of potassium that was isolated from the potash and a pure sodium metal was isolated from the soda ash.

How Did Potassium Get Its Name?

Sir Humphrey Davy kept the old English name for the newly discovered element, calling it ‘potash’, which is short for ‘pot of ash’ – the method previously used to obtain this chemical.

The chemical symbol of potassium (K) represents the initial letter of kalium – the Medieval Latin word for potash. A deeper etymological analysis of this term leads to the Arabic word ‘quali’ that means alkali, i.e. a soluble salt.

Where Can You Find Potassium?

Potassium cannot be found freely in nature. It mostly occurs as a part of mineral formations, such as clay or feldspar. With the weathering of these rock-forming tectosilicate minerals, potassium finds its way to surface waters. Thus, the average potassium concentration in the sea amounts to 0.75 grams per liter.

For commercial purposes, this alkali metal is most often obtained by mining the minerals alunite, carnallite, langbeinite, polyhalite, and sylvite. The largest potassium mines in the world are located in the United States, Germany, Canada, New Mexico, Utah, and Chile.  

Element 19 is also found in almost all plants and animals, as well as inside the human body. Since it reacts strongly with water, potassium is one of the most important minerals that support various biological functions in living organisms.

Potassium in Everyday Life

Although the pure, elemental form of potassium has limited use in everyday life, the various compounds of this chemical element have numerous applications. Especially notable are the uses of potassium chloride, potassium sulfate, and potassium nitrate. These compounds have been extensively used in agriculture as soil fertilizers.

Potassium and Health

The most vital role of this alkali is in the biological processes of living organisms, especially humans. According to the American Heart Association, potassium is responsible for lowering blood pressure, maintaining a balanced water level, muscle contractions, activation of nerve impulses, brain and heart function, reflexes, maintaining the brain-blood supply system, etc. 

Moreover, potassium is considered to be a nutrient of public health concern by the United States Department of Agriculture (USDA), as failing to consume sufficient levels of the nutrient can increase the risk of stroke, hypertension, heart failure, and other types of cardiac diseases.

Potassium-Rich Foods

Since it’s not normally produced in the body, the daily intake of foods that contain a high level of potassium is strongly recommended. Some great sources of potassium include:

  • Bananas;
  • Avocados;
  • Oranges;
  • Cantaloupe;
  • Apricots;
  • Grapefruit;
  • Prunes;
  • Raisins;
  • Dates;
  • Sweet potatoes;
  • Mushrooms;
  • Peas;
  • Cucumbers;
  • Zucchini;
  • Pumpkins;
  • Leafy greens;
  • Orange juice;
  • Tomato juice;
  • Tuna;
  • Halibut;
  • Cod;
  • Trout;
  • Rockfish;
  • Kidney beans;
  • Soybeans;
  • Lima beans;
  • Lentils;
  • Nuts;
  • Low-fat dairy products;
  • Meat and poultry;
  • Brown and wild rice;
  • Bran cereal;
  • Whole-wheat bread.

There are many benefits of consuming potassium in daily nutrition. A potassium-rich diet may prevent strokes, high blood pressure, osteoporosis, and the formation of kidney stones; it can improve bone health, and it can reduce water retention by lowering sodium levels in the body. However, it’s important that these potassium-rich foods are consumed fresh. Processing them decreases their level of dietary potassium.

You may wish to seek medical advice from your healthcare practitioner on the recommended daily intake of potassium for your body.

How Dangerous Is Potassium?

A balanced diet with an adequate intake of potassium is certainly something that we should strive for in order to maintain optimal health, as both low blood potassium levels (hypokalemia) and excess blood potassium levels can lead to adverse medical conditions. The potassium concentration is typically determined by blood tests that measure the levels of potassium contained in your blood. These tests are labeled as ‘serum potassium tests’. 

Hyperkalemia (High Potassium Levels)

Accumulation of high levels of potassium (hyperkalemia) in the body due to the intake of potassium-rich foods typically has no adverse health effects on people with normal kidney function, as the excess amount of this element can be excreted from the body through urine. However, for people with chronic kidney disease (CKD), this function may be disrupted. These individuals may experience:

  • Excess levels of potassium in their blood;
  • Abnormal heartbeat, i.e. cardiac arrhythmia;
  • Constricted brain-blood supply.

In the case of hyperkalemia, it’s strongly advised for the potassium intake to be controlled. In this regard, high-potassium foods, salt substitutes, potassium supplements, and herbal remedies are to be avoided. 

Hypokalemia (Low Potassium Levels)

According to the National Institutes of Health, a normal potassium level is considered to be between 3.5 and 5.0 millimoles per liter (mmol/L). If the potassium levels fall below 3.5 mmol/L, hypokalemia occurs. Potassium deficiency in the blood typically triggers the following side-effects and health conditions: 

  • Kidney disease;
  • Extreme tiredness; 
  • Diarrhea; 
  • Muscle weakness;
  • Vomiting; 
  • Magnesium deficiency; 
  • Irregular heartbeat;
  • Cardiovascular diseases;
  • Excessive sweating;
  • Inability of the body to generate nerve impulses.

Environmental Effects of Potassium

As a macronutrient that is necessary for the life of all living beings, potassium isotopes are included in the nutrient cycling studies. Along with nitrogen and phosphorus, potassium is one of the most essential elements for the growth and survival of plants, since it participates in the maintenance of the osmotic pressure and regulates cell size. This process promotes the growth of plants.

Isotopes of Potassium

Potassium (K) has 26 forms, of which only three isotopes occur naturally: 39K (93.3%), 41K (6.7%), and 40K (0.012%). While the potassium-39 and potassium-41 isotopes are stable, the 40K isotope is a radioactive form of potassium. This radioisotope characterizes an extremely long half-life of decay, which amounts to 1.248×109 years. The least stable potassium isotope is 31K. Its half-life to decay is less than 10 picoseconds. 


[n 1]

ZNIsotopic mass (Da)[7]

[n 2][n 3]


[n 4][n 5]





[n 6]

Spin and


[n 7][n 5]

Natural abundance (mole fraction)
Excitation energy[n 5]Normal proportionRange of variation
31K[4][5]1912 <10 ps3p28S   
33K191433.00756(21)#<25 nsp32Ar3/2+#  
34K191533.99869(21)#<40 nsp33Ar1+#  
35K191634.9880054(6)178(8) msβ+ (99.63%)35Ar3/2+  
β+, p (.37%)34Cl 
36K191735.9813020(4)341(3) msβ+ (99.95%)36Ar2+  
β+, p (.048%)35Cl 
β+, α (.0034%)32S 
37K191836.97337589(10)1.2365(9) sβ+37Ar3/2+  
38K191937.96908112(21)7.636(18) minβ+38Ar3+  
40K[n 8][n 9]192139.96399817(6)1.248(3)×109 yβ (89.28%)40Ca4−1.17(1)×10−4 
EC (10.72%)40Ar 
β+ (0.001%)[8] 
42K192341.96240231(11)12.355(7) hβ42Ca2−  
43K192442.9607347(4)22.3(1) hβ43Ca3/2+  
44K192543.9615870(5)22.13(19) minβ44Ca2−  
45K192644.9606915(6)17.8(6) minβ45Ca3/2+  
46K192745.9619816(8)105(10) sβ46Ca2−  
47K192846.9616616(15)17.50(24) sβ47Ca1/2+  
48K192947.9653412(8)6.8(2) sβ (98.86%)48Ca1−  
β, n (1.14%)47Ca 
49K193048.9682108(9)1.26(5) sβ, n (86%)48Ca(3/2+)  
β (14%)49Ca 
50K193149.972380(8)472(4) msβ (71%)50Ca0−  
β, n (29%)49Ca 
51K193250.975828(14)365(5) msβ, n (65%)50Ca3/2+  
β (35%)51Ca 
52K193351.98160(4)110(4) msβ, n (74%)51Ca2−#  
β (23.7%)52Ca 
β, 2n (2.3%)50Ca 
53K193452.98680(12)30(5) msβ, n (64%)52Ca(3/2+)  
β (26%)53Ca 
β, 2n (10%)51Ca 
54K193553.99463(64)#10(5) msβ (>99.9%)54Ca2−#  
β, n (<.1%)53Ca 
55K193655.00076(75)#3# msβ55Ca3/2+#  
β, n54Ca 
56K193756.00851(86)#1# msβ56Ca2−#  
β, n55Ca 
57K[9][2]1938  β57Ca   
59K[2][n 10]1940       

Source: Wikipedia

List of Potassium Compounds 

Since it’s a highly reactive chemical element, potassium forms a great variety of compounds. The list of more significant potassium compounds includes the following substances:

  • Potassium Permanganate
  • Potassium Iodite
  • Potassium Hypochlorite
  • Potassium Phosphate
  • Potassium Oxalate
  • Potassium Chromate
  • Potassium Hydrogen Phthalate
  • Potassium Dichromate
  • Potassium Chloride
  • Potassium Nitrate
  • Potassium Carbonate
  • Potassium Hydroxide
  • Potassium Sulfate
  • Potassium Bromite
  • Potassium Hydrogen Phosphate
  • Potassium Hydrogen Carbonate
  • Potassium Iodide
  • Monopotassium Phosphate
  • Potassium Chlorate
  • Potassium Hypoiodite
  • Potassium Oxide
  • Potassium Hydrogen Sulfate
  • Potassium Perchlorate
  • Potassium Bromide
  • Potassium Hypobromite
  • Potassium Perbromate
  • Potassium Sulfite
  • Potassium Phosphide
  • Potassium Sulfide
  • Potassium Acetate
  • Potassium Dihydrogen Phosphite

5 Interesting Facts and Explanations

  1. Potassium is the first metal that was isolated through electrolysis. 
  2. About 98% of the potassium in our body is found inside our cells. The muscle-building cells use up the largest quantity of this trace element, which is over 80%. 
  3. The toxins released in our body by a snake bite, a scorpio sting, or a bee sting disrupt the cells’ mechanism for the integration of potassium during some of the most vital biological processes. This is why those bites and stings can sometimes be deadly. 
  4. The term alkali refers to a soluble salt obtained from the ashes of plants. It’s mostly made up of potassium and sodium carbonate. 
  5. Due to the fact that it has less electrons, a potassium ion (K+) has a smaller ionic radius than a potassium atom (K)