Consider the formaldehyde (CH2O molecule What is the central atom? Enter its chemical symbol How many lone pairs are around the central atom?I olo What is the ideal angle between the carbon-hdogen bonds? Compared to the ideal angle, you would expect the actual angle between the carbon-hydrogen bonds to
The Correct Answer and Explanation is :
Answer:
- Central atom: The central atom in the formaldehyde molecule (CH₂O) is carbon (C).
- Lone pairs around the central atom: There are zero (0) lone pairs around the carbon atom.
- Ideal angle between the carbon-hydrogen bonds: The ideal bond angle in a molecule with a trigonal planar geometry, such as CH₂O, is 120°.
- Comparison with the ideal angle: The actual angle between the carbon-hydrogen bonds is slightly less than 120° due to the repulsion caused by the double bond between carbon and oxygen.
Explanation:
Formaldehyde (CH₂O) has the molecular formula CH₂O and consists of one carbon atom, two hydrogen atoms, and one oxygen atom. Here’s a detailed breakdown:
- Central Atom:
- The carbon atom serves as the central atom because it can form the required number of bonds (four, via covalent bonding) and is the least electronegative element in the molecule.
- Lone Pairs Around Carbon:
- The central carbon atom is bonded to two hydrogen atoms and one oxygen atom (via a double bond). All four of carbon’s valence electrons are used in bonding, leaving no lone pairs on the carbon atom.
- Molecular Geometry:
- Formaldehyde adopts a trigonal planar geometry around the carbon atom because it has three regions of electron density (two C-H single bonds and one C=O double bond). This geometry minimizes electron repulsion, resulting in an ideal bond angle of approximately 120°.
- Deviation from the Ideal Angle:
- The double bond between carbon and oxygen introduces a greater electron density, causing stronger electron repulsion compared to the single bonds. This compresses the angle between the two C-H bonds, making it slightly less than 120°.
Importance of Bond Angles:
The bond angle affects the molecule’s polarity and reactivity. In CH₂O, the slight compression of bond angles contributes to its overall polar nature due to the unequal distribution of electrons between the carbon, oxygen, and hydrogen atoms.