The net charge on a sulfide ion (S^2-) is 2-. How does this ion obtain its charge?

The sulfide ion, denoted as S²⁻, carries a net charge of 2- due to the gain of electrons. To understand how this happens, let's break it down step by step.

Understanding Atomic Structure

Every atom consists of protons, neutrons, and electrons. Protons, which are positively charged, reside in the nucleus, while negatively charged electrons orbit around the nucleus. In a neutral atom, the number of protons equals the number of electrons, balancing the overall charge.

The Sulfur Atom

Sulfur, with the atomic number 16, has 16 protons and, in its neutral state, also has 16 electrons. This balance means that the sulfur atom has no net charge.

The Process of Ion Formation

When sulfur forms an ion, it can either lose or gain electrons. In the case of the sulfide ion, sulfur gains electrons. This process typically occurs when sulfur reacts with metals or other elements that have a tendency to donate electrons.

Gaining Electrons

To achieve a more stable electron configuration, sulfur tends to gain two additional electrons. This is because sulfur is in Group 16 of the periodic table and needs two more electrons to fill its outer shell, achieving the stable electron configuration similar to that of noble gases.

• Neutral Sulfur Atom: 16 protons, 16 electrons (0 charge)
• After Gaining Electrons: 16 protons, 18 electrons (2- charge)

Resulting Charge of the Sulfide Ion

By gaining these two electrons, the sulfide ion now has a total of 18 electrons. Since there are still only 16 protons in the nucleus, the overall charge becomes negative. Specifically, the charge is calculated as follows:

Charge = Number of Protons - Number of Electrons

Charge = 16 - 18 = -2

Stability of the Ion

This 2- charge indicates that the sulfide ion is now more stable in chemical reactions, particularly with metals that can lose electrons easily, forming ionic compounds. For example, when sulfide ions combine with metal ions like sodium (Na⁺), they form sodium sulfide (Na₂S), a stable compound.

In summary, the sulfide ion obtains its 2- charge by gaining two electrons, leading to an imbalance between the number of protons and electrons. This process is a fundamental aspect of how elements interact to achieve stability through ionic bonding.