The chemical formula of Rubidium (Rb) sulfide is Rb2S.
The Correct Answer and Explanation is:
The chemical formula of Rubidium (Rb) sulfide is Rb₂S.
Explanation
The chemical formula for an ionic compound like rubidium sulfide is determined by the principle of charge neutrality. This principle states that for a stable compound to form, the total positive charge from the cations must exactly balance the total negative charge from the anions.
1. Identifying the Ions and Their Charges:
First, the constituent elements must be identified as a metal and a non-metal, which indicates an ionic bond will form through the transfer of electrons.
- Rubidium (Rb): Rubidium is an element in Group 1 of the periodic table, the alkali metals. Elements in this group have one valence electron. To achieve a stable electron configuration, similar to the nearest noble gas, rubidium will readily lose this single electron. Losing one negatively charged electron results in the formation of a cation with a positive charge of 1+. The rubidium ion is therefore written as Rb⁺.
- Sulfur (S): Sulfur is in Group 16 of the periodic table. Elements in this group have six valence electrons. To achieve a stable octet, sulfur has a strong tendency to gain two electrons. Gaining two negatively charged electrons results in the formation of an anion with a charge of 2-. This ion is called the sulfide ion and is written as S²⁻.
2. Balancing the Charges:
The next step is to combine these ions in a ratio that results in a net charge of zero. A single rubidium ion (Rb⁺) has a +1 charge, while a single sulfide ion (S²⁻) has a –2 charge. These do not balance.
To achieve neutrality, two rubidium ions are required to balance the charge of one sulfide ion. The total positive charge from two Rb⁺ ions is (2 × +1) = +2. This +2 charge perfectly cancels out the –2 charge of a single S²⁻ ion.
(2 × Rb⁺) + (1 × S²⁻) → (+2) + (–2) = 0
3. Writing the Chemical Formula:
The chemical formula reflects this simplest whole-number ratio of ions. By convention, the cation is written first, followed by the anion. The number of each ion required for neutrality is written as a subscript after the element’s symbol. In this case, the ratio is two rubidium ions to one sulfide ion.
Therefore, the formula is written as Rb₂S. The subscript ‘2’ applies to rubidium, and the subscript for sulfur is ‘1’, which is implied and not written.
