Question

Put the following three molecules in order of increasing h–x–h bond angle, where x is the central atom.

1) CH₄ < H₂S < PH₃
2) H₂S < PH₃ < CH₄
3) CH₄ < PH₃ < H₂S
4) PH₃ < CH₄ < H₂S

Answer 1

The molecules CH₄ (methane), H₂S (hydrogen sulfide), and PH₃ (phosphine) should be ordered based on their molecular geometries and the repulsion between electron pairs, resulting in the correct order of increasing H–X–H bond angle being H₂S < PH₃ < CH₄.

Step-by-step explanation:

The question asks to put the molecules CH₄ (methane), H₂S (hydrogen sulfide), and PH₃ (phosphine) in order of increasing H–X–H bond angle, where X represents the central atom. The bond angles are influenced by the electronegativity of the atoms and the molecular geometries. Methane (CH₄) has a tetrahedral geometry with bond angles of approximately 109.5 degrees. Phosphine (PH₃) has a trigonal pyramidal geometry with smaller bond angles due to the lone pair of electrons on the phosphorus atom, resulting in bond angles less than 109.5 degrees but greater than 90 degrees. Hydrogen sulfide (H₂S) has a bent geometry similar to water, with bond angles even smaller than PH₃ due to increased lone pair repulsion. Therefore, the correct order of increasing H–X–H bond angle is H₂S < PH₃ < CH₄.