Potassium has an atomic number 19 and is located in group 1 of the s-block. It is located in the fourth period. It is classified under alkali earth metals as it belongs to group one. Though potassium is very abundant in nature, it is usually never found in the free state due to its high reactivity.
Like other elements of group 1, potassium has incompletely filled s orbital. The electronic configuration of potassium is 1s2 2s2 2p6 3s2 3p6 4s1. The electrons per shell are 2,8,8,1.
Thus we can see that by losing only one electron, it can achieve a stable noble gas configuration. Thus potassium is highly electropositive. It also has a large radius(atomic radius =227 pm) and can lose one electron easily.
Potassium is designated with the symbol K. K stands for Kalium which is the Latin name for potassium. The atomic mass of potassium is 39.09 AMU. Three isotopes (of mass numbers 39,40 and 41) of potassium can be found in nature. The isotope with mass number =40 is radioactive in nature.
Potassium is silvery gray in appearance. On exposure to oxygen in the air, it begins to tarnish. Potassium is the lightest metal after lithium, so it has a very low density. It melts at around 63 degrees Celsius and is a soft solid metal at room temperature.
Since there is only one electron in its outer shell, it has low ionization enthalpy and loses an electron easily. Thus it is highly reactive. During flame, test potassium gives a lilac color as the electrons get excited to the empty orbitals present.
Due to potassium’s large size and low ionization enthalpy, potassium is highly reactive and gets oxidized easily. Potassium can lose one electron easily to form a potassium cation. However, after losing one electron, it attains a stable noble gas configuration, and thus second ionization enthalpy is very high. Potassium forms ionic compounds.
Potassium tarnishes easily in the air due to its high reactivity to form potassium peroxide. Potassium may also form superoxides. The O2 – ion is only stable when bonded to large cations like K+.
2K+ O2 →K2O2 (peroxide)
K+ O2 →KO2 (superoxide)
Potassium, like other alkali metals, reacts with water to give potassium hydroxide and dihydrogen.
2K + 2H2O→2K+ + 2OH- +H2
Potassium reacts explosively with water releasing much heat (exothermic reaction).
Due to potassium’s highly reactive nature, potassium is usually stored in kerosene oil so that it does not react to oxygen and moisture in the air.
Potassium reacts readily with halogens (releasing heat, exothermic reaction) to form ionic halides. The halides include potassium fluoride, potassium chloride, potassium bromide, and potassium iodide. Potassium loses one electron easily to achieve the closest noble gas configuration, thus donating this electron to a halogen atom so that they also attain stable electronic configuration. The potassium cation and halide anion then bond due to ionic forces.
Potassium reacts with dihydrogen gas to form potassium hydride at a temperature of about 680 Kelvin. Potassium hydride is an ionic solid at room temperature.
2K + H2→ 2 KH
As it donates an electron easily, it has a basic nature. Oxides and carbonates of potassium are basic in nature. Potassium hydroxide is a highly alkaline compound.
Potassium can donate electrons easily(to achieve stable configuration) thus, it gets oxidized and acts as a reducing agent. Potassium has a high negative electrode potential; thus, it is a good reducing agent.
Compounds of potassium
It is paramagnetic in nature because it has an unpaired electron in π*2p orbital. In water, it gets hydrolyzed and gives potassium hydroxide.
2KO2 +2H2O→ 2KOH + H2O2 + O2
This KOH is highly basic.
It has a crystalline structure and is white in color. It is a strong base and is alkaline in nature. When dissolved in water, potassium hydroxide releases much heat due to hydration. It is a popular reagent in qualitative analysis and is used to make multiple salts. It is also used to produce a basic medium.
All the potassium halides are soluble in water. They are all ionic. The halides have a crystalline structure and have high melting points. They are solids at room temperature. Potassium forms halides easily on reacting with the respective hydrogen acid.
Carbonates and bicarbonates
Potassium carbonate and potassium bicarbonate are both basic salts. They are stable to thermal decomposition.
1. Potassium is a major chemical in most fertilizers. It is a macro-mineral. Compounds of potassium that are used are potassium nitrate, potassium chloride, etc.
2. Potassium is used to make glass. In this case, potassium carbonate is used.
3. Potassium hydroxide and potassium carbonate are used to make specific kinds of soap and detergents.
4. In nuclear reactors as potassium alloy is used where it is mixed with sodium. It acts as a heat transfer medium.
5. Potassium superoxide is used in respiratory equipment. It can release oxygen from water vapor and carbon dioxide.
2KO2 + H2O + 2CO2 => 2KHCO3 + O2
6. Potassium is used to make batteries, gun powder, dyes, etc.
Potassium is used in the extraction of valuable minerals like gold mining.
7. It is used to regulate the pH of different mediums and provide a basic medium. It is also used as a catalyst in multiple reactions.
8. Potassium is used to regulate high blood pressure and stroke.
9. Potassium is used to make Benedict’s reagent used for qualitative analysis.
Potassium in the body
The concentration of potassium is more in the intracellular fluid than in the extracellular fluid. The kidney regulates potassium balance in the blood. Potassium is essential for preventing the formation of kidney stones.
Potassium is involved in maintaining the osmotic pressure of blood. It is involved in maintaining the balance between extracellular fluid and intracellular fluid. It maintains the pH balance of the blood.
Potassium is essential in transferring nerve and muscle impulses. It is essential for muscle contraction.
When a nerve gets stimulated, three sodium ions are pumped out, and two potassium ions are pumped in (via sodium-potassium pump). This forms a potential difference at that point and current flow, thus conducting the nerve impulse from that point to the adjacent point. Thus the nerve impulse gets transmitted.