How many “central” atoms are part of methanol (CH3OH)? What are the molecular geometries of each central atom?
The correct answer and explanation is:
Methanol (CH₃OH) has two central atoms: carbon (C) and oxygen (O). These atoms are considered central because they are bonded to other atoms and form the core structure of the molecule.
- Carbon (C): The carbon atom in methanol is bonded to three hydrogen atoms and one hydroxyl group (-OH). Carbon has four bonds in total, fulfilling its requirement of four valence electrons. Since the carbon atom is bonded to four atoms, it adopts a tetrahedral geometry. This means that the bond angles around the carbon atom are approximately 109.5°, which is characteristic of a tetrahedral shape.
- Oxygen (O): The oxygen atom in methanol is bonded to one hydrogen atom and to the carbon atom via a single bond. Oxygen has two lone pairs of electrons in addition to the bonds it forms. Given that it has two bonds and two lone pairs, the oxygen atom adopts a bent (or angular) geometry. The bond angles around oxygen are slightly less than 109.5° because lone pairs exert more repulsive forces than bonding pairs. This results in a bond angle closer to 104.5°.
To summarize:
- Carbon (C): Tetrahedral geometry with bond angles around 109.5°.
- Oxygen (O): Bent geometry with bond angles around 104.5°.
Both atoms follow the principles of valence shell electron pair repulsion (VSEPR) theory, which helps determine the geometries by considering the repulsion between bonding and nonbonding electron pairs. In methanol, the tetrahedral shape of carbon and the bent shape of oxygen allow the molecule to maintain its stable structure and exhibit its characteristic properties.