how does the number of electron pairs around a central atom determines its shape
Read about VSEPR theory.
The number of electron pairs around a central atom plays a crucial role in determining its shape. The arrangement of electron pairs is governed by the concept of valence shell electron pair repulsion theory (VSEPR theory), which states that valence electron pairs, whether bonding or non-bonding, repel each other and try to get as far away from each other as possible in three-dimensional space.
To determine the shape, follow these steps:
1. Draw the Lewis dot structure of the molecule or ion.
2. Determine the number of electron pairs around the central atom. Count both the bonding and non-bonding electron pairs.
3. Based on the number of electron pairs, use the following rules to predict the molecular geometry:
- 2 electron pairs: The molecular geometry will be linear.
- 3 electron pairs: The molecular geometry will be trigonal planar.
- 4 electron pairs: The molecular geometry will be tetrahedral.
- 5 electron pairs: The molecular geometry will be trigonal bipyramidal.
- 6 electron pairs: The molecular geometry will be octahedral.
4. Determine the steric number of the central atom, which is equivalent to the number of electron pairs around it. This will help you determine the hybridization of the central atom.
5. Identify the positions of electron pairs, including both bonding and non-bonding pairs, using the VSEPR theory. These positions define the molecular shape.
Remember, electron pairs can be either bonding pairs (shared electrons in covalent bonds) or non-bonding pairs (lone pairs of electrons that do not participate in bonding). Both types of electron pairs contribute to the overall shape of the molecule or ion.
Additionally, there might be slight deviations from the ideal bond angles due to factors such as lone pair repulsions, but generally, the number of electron pairs provides a good indication of the molecule's shape.