Final answer:
Condensed structural formulas represent the arrangement of atoms in a molecule, and the molecular geometry around carbon atoms is typically tetrahedral for alkanes (single bonded) and trigonal planar for alkenes (double bonded).
Step-by-step explanation:
Molecular Geometry and Condensed Structural Formulas
The question asks for condensed structural formulas and the description of molecular geometry at each carbon atom for a series of compounds. In a condensed structural formula like CH3CH3, the molecular geometry around each carbon is tetrahedral, with bond angles close to 109.5°. For CH2CH2, the geometry is not given as trigonal planar; each carbon in ethene (ethylene) has a trigonal planar geometry because it is involved in a double bond. CH3CH2CH3 (propane) also has a tetrahedral geometry at each carbon atom since there are only single bonds present. For CH3CHO (acetaldehyde), the geometry around the methyl carbon is tetrahedral, while the carbonyl (C=O) carbon is trigonal planar due to the double bond.
The molecular geometry is dictated by the hybridization of the carbon atoms and the types and numbers of bonds they form. In alkanes with only single bonds (sp³ hybridized), the geometry is tetrahedral, while the presence of double bonds (sp² hybridized) in alkenes results in a trigonal planar geometry.