To draw the Lewis structure for PH3 (phosphine), follow these steps:
1. **Count the total number of valence electrons**: Phosphorus (P) has 5 valence electrons, and each hydrogen (H) has 1 valence electron. Since there are 3 hydrogen atoms, the total number of valence electrons is 5 + (3 × 1) = 8.
2. **Place the least electronegative atom in the center**: Phosphorus is less electronegative than hydrogen, so it will be the central atom.
3. **Connect the atoms with single bonds**: Draw single bonds between the phosphorus atom and each hydrogen atom. This uses 6 of the 8 valence electrons (3 bonds × 2 electrons each).
4. **Distribute the remaining electrons**: The remaining 2 electrons are placed as a lone pair on the phosphorus atom.
**Bonds and Non-Bonding Pairs**:
– **Bonds**: There are 3 single bonds between phosphorus and each hydrogen atom.
– **Non-Bonding Pairs**: There is 1 lone pair of electrons on the phosphorus atom.
**Molecular Shape**:
The shape of PH3 is **trigonal pyramidal**. This is because the lone pair on the phosphorus atom repels the bonding pairs, causing the hydrogen atoms to arrange themselves in a pyramidal shape around the phosphorus atom.
In summary, the Lewis structure for PH3 shows 3 bonds and 1 non-bonding pair around the central phosphorus atom, resulting in a trigonal pyramidal molecular shape.