Potassium Charge: The Nuclear Charge, Effective Nuclear Charge & The Reactions

By itself, the potassium atom carries no charge. However, when it loses an electron to anions like the halides, it gets a positive charge. The potassium cation has a lot of biological importance to both plants and animals. But, this is not the case study here.

This article looks into the ionic charge, nuclear charge, effective nuclear charge, and unique characteristics of potassium.

Properties of potassium

  • Potassium is a soft silvery-white metal that turns bluish-purple when it comes in contact with air
  • It is a group 1 metal located in period 4
  • It has an atomic number of 19 and a mass number of 39
  • Potassium was first isolated from potash and it naturally occurs in ionic salts
  • Furthermore, upon exposure to atmospheric oxygen, potassium forms potassium peroxide, a white flaky substance
  • Potassium is one of those metals that exhibit only one oxidation state (+1)
  • Potassium has an electronic configuration of 1s22s22p63s23p64s1 with 2, 8, 8, 1 electrons in its shells
  • In addition, it is a solid at STP and has a boiling point of 1395.7°F (757.643°C), a melting point of ​146.3°F (63.5°C), and a density of 0.89 g/cm3 (near room temperature) and 0.82948 g/cm3 (when it turns liquid at its melting point)

What is the charge of potassium when it forms an ion?

The potassium ion, K+, has a +1 charge. As a metal, it forms a cation when it loses one electron and gains a positive charge. In its ionic form, potassium readily binds to anions to form organic and inorganic salts.

What is the nuclear charge of potassium?

The nuclear charge of potassium is the total amount of charge on the protons in the nucleus. It is also the same as the atomic number of that element. Therefore, the nuclear charge of potassium is 19.

What is the effective nuclear charge of potassium?

You can determine the effective nuclear charge, Zeff, of the valence electron in potassium as follows:

Zeff = Z – S

Z is the nuclear charge or the number of protons or the atomic number and S is the shielding constant which we can find using Slater’s rule as follows:

  • Electronic configuration of potassium: 1s22s22p6, 3s23p6, 4s1
  • Then, assign electron value to the electrons in the shells
  • 4s1, the electron of concern will have no electron value
  • Electrons in (n-1) shell (3s23p6) will have a shielding effect of 0.85
  • The electrons in the lower shell (n-2) (1s22s22p6) will have a shielding effect of 1
  • Therefore, the shielding constant will be (0.85 x 8) + (1 x 10) = 16.8

The nuclear charge, Z, is 19. Substitute the values into the formula for Zeff

Zeff = 19 – 16.8

Zeff= 2.20

What are the chemical reactions potassium undergoes?

Reaction with air

Potassium is a soft metal that quickly reacts with oxygen. Upon contact with oxygen, the silvery-white metal turns into a dull bluish-purple metal.

Potassium oxidizes into potassium superoxide upon contact with air.

K(s) + O2(g) → KO2(s)

Reaction with halogens

Just like sodium, potassium reacts with the halogens (F, Cl, Br, and I) to form potassium halides (KF, KCl, KBr, and KI).

Reaction with acids

When potassium metal dissolves in sulphuric acid, it forms a solution that contains aqueous potassium, aqueous sulfate, and hydrogen gas.

2K(s) + H2SO4(aq) → 2K+(aq) + SO42-(aq) + H2(g)

Reaction with bases

When potassium reacts with water, it rapidly forms a basic solution of potassium hydroxide and gives off hydrogen gas. This exothermic reaction resembles the dissolution of sodium in water that firms sodium hydroxide but it is more rapid.

2K(s) + 2H2O → 2KOH(aq) + H2(g)

Is the valency of potassium the same as its charge?

Yes. Although not all elements have the same valency and charge, potassium does. It has an electronic configuration of 1s22s22p63s23p64s1. It has only one electron in its valence shell, which implies a valency of +1.

Does potassium form salts?

Potassium forms salts with anions after it has lost one electron to form the K+ ion. In nature, potassium occurs in salts. It can bind with anions to form salts that range from edible to inedible.

Examples of salts of potassium include potassium chloride (KCl), potassium permanganate (KMnO4), potassium nitrate or saltpeter (KNO3), alum or potassium aluminum sulfate (KAl(SO4)2), potash or potassium carbonate (K2CO3).

Other salts of potassium include potassium salts of fatty acids that may include oleate, myristate, and laureate which are formed by adding potassium hydroxide to fatty acids.


What is the charge of K in K2Cr2O7?

The charge of potassium in K2Cr2O7 is +1. Substitute the oxidation state of all atoms in the compound. Cr is a +6 oxidation state in this compound and O is in an oxidation state of -2. The overall charge of the compound is 0.

2K + 2(6) + 2(-7) = 0

2K – 2 = 0

K = +1

What is the charge of K in KMnO4?

In KMnO4, K has a charge of +1. In potassium permanganate, Mn has an oxidation state of +7 and O is in its -2 oxidation state.

K + 7 + 4(-2) = 0

K = +1

Can potassium form anions?

Potassium is a metal and a member of the group one element, so it cannot form anions. Although, K has been seen to occur in some compounds but it is very rare. Potassium is a monovalent atom that loses one electron to form a cation.


Potassium does not have eight electrons in its outermost shell. To attain stability, it loses the single electron it has in its valence shell and the neutral atom carries a charge.

Many metals can exhibit multiple oxidation states and charges. Potassium is not one of these. Potassium ion is a monocation. However, in a few cases, it forms an anion.

Potassium is one of the very reactive metals. It readily forms salts with anions and fatty acids.

Read this article to learn about the charge of magnesium.

Thanks for reading.