A. What is the electron pair geometry for Be in BeCl2?
There are lone pair(s) around the central atom, so the geometry of BeCl2 is _
B. What is the electron pair geometry for P in POCl3?
There are _ lone pairs around the central atom, so the geometry of POCl3 is __
The Correct Answer and Explanation is:
A.
- Electron pair geometry for Be in BeCl₂: Linear
- There are 0 lone pair(s) around the central atom, so the geometry of BeCl₂ is Linear
B.
- Electron pair geometry for P in POCl₃: Tetrahedral
- There are 0 lone pairs around the central atom, so the geometry of POCl₃ is Tetrahedral
Explanation:
To determine molecular geometry, we use the Valence Shell Electron Pair Repulsion (VSEPR) theory, which predicts the spatial arrangement of atoms based on repulsions between electron pairs around a central atom.
A. BeCl₂ (Beryllium Dichloride):
Beryllium (Be) is the central atom, bonded to two chlorine (Cl) atoms. Be has 2 valence electrons and forms two single bonds with Cl atoms, using up all its valence electrons. Importantly, beryllium does not follow the octet rule — it is stable with only 4 electrons. Since there are no lone pairs on Be, the two bonding electron pairs repel each other and move as far apart as possible, resulting in a linear geometry with a bond angle of 180°.
- Electron domains: 2 (both bonding)
- Lone pairs on Be: 0
- Electron pair geometry: Linear
- Molecular geometry: Linear
B. POCl₃ (Phosphoryl Chloride):
Phosphorus (P) is the central atom bonded to one oxygen (double bond) and three chlorine atoms (single bonds). This gives a total of 4 regions of electron density around phosphorus: one double bond and three single bonds. Each double or single bond counts as one electron domain in VSEPR theory. There are no lone pairs on phosphorus.
With 4 electron domains and no lone pairs, the electron pair geometry is tetrahedral. Since all electron domains are bonding and there are no lone pairs to distort the shape, the molecular geometry is also tetrahedral, with bond angles close to 109.5°.
- Electron domains: 4 (1 double bond, 3 single bonds)
- Lone pairs on P: 0
- Electron pair geometry: Tetrahedral
- Molecular geometry: Tetrahedral
These geometries determine physical properties like polarity and molecular interactions, which are vital in chemical reactivity and function.
