The phosphonium ion, PH4+, is formed by reaction of phosphine, PH3, with an acid. (a) Draw the Lewis structure of the phosphonium ion. (b) Predict its molecular geometry. (c) Describe how a fourth hydrogen can be added to PH3. (d) Explain why the ion has a +1 charge
The correct answer and explanation is:
(a) Lewis Structure of PH₄⁺
To draw the Lewis structure of PH₄⁺, follow these steps:
- Determine the total valence electrons:
- Phosphorus (P) has 5 valence electrons.
- Hydrogen (H) has 1 valence electron each, contributing a total of 4 electrons.
- Since the ion has a +1 charge, one electron is removed.
- Total valence electrons = 5 + (4 × 1) – 1 = 8 electrons.
- Draw the skeletal structure:
- Phosphorus is the central atom.
- Four hydrogen atoms are bonded to phosphorus with single bonds.
- Assign electron pairs:
- All 8 electrons are used in bonding, forming four P–H bonds.
- There are no lone pairs on phosphorus.
The Lewis structure consists of a central phosphorus atom with four hydrogen atoms bonded to it through single bonds.
(b) Molecular Geometry
Using VSEPR theory:
- Phosphorus in PH₄⁺ forms four single bonds with hydrogen.
- No lone pairs remain on phosphorus.
- The molecular shape follows the tetrahedral geometry.
- Bond angles are approximately 109.5°.
(c) Addition of a Fourth Hydrogen to PH₃
- Phosphine (PH₃) has a lone pair on phosphorus, making it a Lewis base.
- When PH₃ reacts with a proton (H⁺) from an acid, it donates its lone pair to H⁺, forming a new P–H bond.
- This results in the formation of PH₄⁺.
(d) Charge Explanation
- Neutral PH₃ has 5 valence electrons on phosphorus.
- Upon adding a proton (H⁺), phosphorus shares its lone pair, forming an extra bond.
- Since H⁺ has no electrons, the overall charge increases by +1, leading to PH₄⁺.
Now, I’ll generate the image of the PH₄⁺ Lewis structure.
Here is the Lewis structure diagram of the phosphonium ion (PH₄⁺). Let me know if you need any modifications or further explanations!
