Which is the correct formula for strontium cyanide? SrCN Sr3(CN)2 Sr2(CN)3 SrCN2 Sr(CN)2
The Correct Answer and Explanation is:
The correct formula for strontium cyanide is:
✅ Sr(CN)₂
Explanation (300+ words):
To determine the correct formula for strontium cyanide, we need to understand how to form ionic compounds between a metal (strontium) and a polyatomic ion (cyanide).
Step 1: Understand the Ions
- Strontium (Sr):
- Strontium is an alkaline earth metal, found in Group 2 of the periodic table.
- Group 2 metals typically form +2 cations.
- So, strontium forms the ion Sr²⁺.
- Cyanide (CN):
- Cyanide is a polyatomic ion composed of one carbon atom and one nitrogen atom.
- Its formula is CN⁻, and it carries a -1 charge.
Step 2: Balance the Charges
To write the correct chemical formula, the total positive charge must balance the total negative charge.
- Sr²⁺ provides +2 charge.
- CN⁻ provides -1 charge per ion.
To balance the +2 from Sr²⁺, you need 2 cyanide ions:
- Sr²⁺ + 2 × CN⁻ → Sr(CN)₂
This gives us a neutral compound, where the charges cancel out:
- (+2) + (2 × -1) = 0
Step 3: Use Parentheses for Polyatomic Ions
Since cyanide is a polyatomic ion and you need more than one of them, you must enclose it in parentheses and add a subscript outside:
- Correct format: Sr(CN)₂
- Incorrect: SrCN₂ (suggests 1 Sr, 1 C, 2 N – not valid)
- Incorrect: Sr3(CN)₂ (implies 3 Sr²⁺ and 2 CN⁻ → charges don’t balance)
- Incorrect: Sr2(CN)3 (implies 2 Sr²⁺ = +4, 3 CN⁻ = -3 → not neutral)
✅ Final Answer:
Sr(CN)₂ is the correct formula for strontium cyanide, representing one Sr²⁺ ion and two CN⁻ ions, forming a neutral ionic compound.