Q68P - Chemistry: Molecular Nature Of Matter And Change

Question

Describe the formation of solid potassium sulfide (K₂S) from large numbers of potassium and sulfur atoms.

Step-by-Step Solution

Answer

Two potassium atoms transfer completely a single electron each to one sulfur atom to form ions (cations and anions) which attract each other to form potassium sulfide compound.

Step1: Definition of ionic compounds

The ionic compounds are chemical compounds that are formed from the reaction between reactive (electropositive) metals and reactive (electronegative) nonmetals as shown below. The general chemical formula for binary ionic compounds is expressed as ${\mathbf{M}}_{\mathbf{p}}{\mathbf{X}}_{\mathbf{q}}\mathbf{.}$ . 

 $\mathbf{pM}\mathbf{+}\mathbf{qX}\mathbf{\to }\mathbf{[}{\mathbf{pM}}^{\mathbf{q}\mathbf{+}}\mathbf{+}{\mathbf{qX}}^{\mathbf{P}\mathbf{-}}\mathbf{]}\mathbf{\to }{\mathbf{M}}_{\mathbf{p}}{\mathbf{X}}_{\mathbf{q}}$

Here,  $\mathbf{M}$ is a more electropositive metal and  $\mathbf{X}$ is a more electronegative nonmetal, $\mathbf{p}$ and $\mathbf{q}$  are coefficients/subscripts of $\mathbf{M}$  and $\mathbf{X}$ respectively.

Step 2: Formation of solid potassium sulfide

Solid potassium sulfide is an ionic compound that is formed from the chemical reaction between potassium metal and sulfur nonmetal. In this reaction, each potassium atom donates its single valence electron to form potassium cation, ${\mathbf{K}}^{\mathbf{+}}$  with a positive charge. At the same time, each sulfur atom accepts two electrons from potassium to form sulfur dianion as sulfide anion, ${\mathbf{S}}^{\mathbf{2}\mathbf{-}}$ . These ions are opposite in charges and combine electrostatically to produce solid potassium sulfide, ${\mathbf{K}}_{\mathbf{2}}\mathbf{S}\mathbf{.}$ .