The formula of cesium phosphide is
a. Cs2P3
b. CSP3
c. Cs3P
d. CS3P2
The Correct Answer and Explanation is :
The correct formula for cesium phosphide is c. Cs₃P.
Explanation:
Cesium phosphide is an ionic compound formed between cesium (Cs) and phosphorus (P). To understand why the correct formula is Cs₃P, let’s break down the bonding and the valence electrons of each element involved:
- Cesium (Cs): Cesium is an alkali metal, located in Group 1 of the periodic table. Alkali metals typically form +1 cations because they have one electron in their outermost shell. When cesium loses this electron, it achieves a stable electron configuration similar to the nearest noble gas, xenon. Thus, the cesium ion is Cs⁺.
- Phosphorus (P): Phosphorus is in Group 15 of the periodic table. It typically forms anions with a charge of -3 (P³⁻) because it needs three electrons to complete its valence shell and achieve a stable electron configuration.
- Ionic Bond Formation: When cesium (Cs) combines with phosphorus (P), the cesium atoms donate one electron each to the phosphorus atom. Since phosphorus requires three electrons to achieve a stable configuration, three cesium ions (each contributing one electron) are needed to balance the charge of one phosphorus ion.
- Cs⁺ + Cs⁺ + Cs⁺ = P³⁻
Therefore, three cesium cations are required for every phosphorus anion to form a neutral compound, leading to the formula Cs₃P.
Why the Other Options Are Incorrect:
- a. Cs₂P₃: This would imply that two cesium ions balance three phosphorus ions, which is not the case. The charge balance does not work out because phosphorus needs three electrons, while two cesium ions would only provide two.
- b. CSP₃: This formula suggests one cesium ion for three phosphorus ions, which would not result in a neutral compound either.
- d. Cs₃P₂: This formula suggests three cesium ions balancing two phosphorus ions, which again doesn’t result in a charge balance.
Thus, the correct formula for cesium phosphide is Cs₃P, as it ensures charge neutrality between the cesium and phosphorus ions.