In potassium chloride (KCl), the potassium atom (K) and the chlorine atom (Cl) both contribute valence electrons.
Potassium (K) is located in Group 1 of the periodic table, also known as the alkali metals. The atomic number of potassium is 19, indicating that a neutral potassium atom has 19 electrons. The electron configuration of potassium is [Ar] 4s¹, which means it has one valence electron in the 4s orbital.
Chlorine (Cl) is located in Group 17, also known as the halogens. The atomic number of chlorine is 17, indicating that a neutral chlorine atom has 17 electrons. The electron configuration of chlorine is [Ne] 3s² 3p⁵, which means it has seven valence electrons in the 3s and 3p orbitals.
When potassium and chlorine combine to form KCl, potassium donates its one valence electron to chlorine. As a result, potassium forms a positive ion with a charge of +1 (K⁺), and chlorine forms a negative ion with a charge of -1 (Cl⁻). The ionic bond between K⁺ and Cl⁻ leads to the formation of potassium chloride (KCl).
Therefore, in KCl, the potassium ion (K⁺) has lost its one valence electron, while the chloride ion (Cl⁻) has gained one electron.