How to identify the shape of all non terminal atoms ?
The correct answer and explanation is:
To identify the shape of all non-terminal atoms in a molecule, you must use the Valence Shell Electron Pair Repulsion (VSEPR) theory. This theory helps predict the geometric arrangement of atoms based on the repulsion between electron pairs in the valence shell of the central atom. The steps to determine the shape are as follows:
- Determine the Lewis Structure: Start by drawing the Lewis structure of the molecule, ensuring that the valence electrons are properly placed around the atoms. Non-terminal atoms are typically those that are bonded to more than one atom.
- Identify the Electron Pairs: Count the total number of bonding pairs and lone pairs of electrons around the central atom and the non-terminal atoms. This includes both single, double, and triple bonds as bonding pairs, and any lone pairs of electrons on the atoms.
- Apply the VSEPR Model:
- For each non-terminal atom, consider the number of regions of electron density (bonding or lone pairs) around it.
- Based on the number of electron pairs, the shape of the atom will be determined:
- 2 regions of electron density: linear (180° angle)
- 3 regions: trigonal planar (120° angle)
- 4 regions: tetrahedral (109.5° angle)
- 5 regions: trigonal bipyramidal (90° and 120° angles)
- 6 regions: octahedral (90° angles)
- Account for Lone Pairs: If the non-terminal atom has lone pairs, these influence the geometry. Lone pairs require more space than bonding pairs, and thus may slightly distort the ideal bond angles. For example, in the case of ammonia (NH₃), the nitrogen atom has one lone pair, which leads to a pyramidal shape instead of a perfect tetrahedral arrangement.
- Double and Triple Bonds: Treat double and triple bonds as one region of electron density when determining the shape.
By following these steps, you can identify the molecular shapes of non-terminal atoms, which can then help understand the overall geometry of the molecule and its chemical properties.