Question

what is the formula of the predicted product from heating potassium metal and powdered phosphorous?

k₂p₃

kp₃

kp

k₃p₂

k₃p

Explanation:

Step1: Determine the charges of ions

Potassium (\(K\)) is in Group 1 of the periodic table. So, it forms \(K^{+}\) ion (charge \(+ 1\)). Phosphorus (\(P\)) is in Group 15. It gains 3 electrons to achieve a stable octet and forms \(P^{3 -}\) ion (charge \(-3\)).

Step2: Use the criss - cross method for formula writing

For an ionic compound, the formula is determined by balancing the charges. We need to find the ratio of \(K^{+}\) and \(P^{3-}\) such that the overall charge is zero. Let the number of \(K^{+}\) ions be \(x\) and \(P^{3-}\) ions be \(y\). Then \(x\times(+1)+y\times(- 3)=0\). If \(y = 1\), then \(x=3\).

Answer:

\(K_{3}P\)