a. Why is the SO₃ molecule trigonal planar but the SO₃^2– ion is trigonal pyramidal?

검증된 단계별 안내

Determine the number of valence electrons for each species: SO_3 and SO_3^{2-}.

For SO_3, sulfur (S) has 6 valence electrons and each oxygen (O) has 6 valence electrons, totaling 24 valence electrons.

For SO_3^{2-}, add 2 extra electrons to the total from SO_3 due to the 2- charge, resulting in 26 valence electrons.

Draw the Lewis structures for both SO_3 and SO_3^{2-}, ensuring to distribute electrons to satisfy the octet rule where possible.

Use VSEPR theory to determine the molecular geometry: SO_3 has no lone pairs on the central sulfur, resulting in a trigonal planar shape, while SO_3^{2-} has one lone pair on sulfur, leading to a trigonal pyramidal shape.

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주요 개념

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Molecular Geometry

Molecular geometry refers to the three-dimensional arrangement of atoms within a molecule. It is determined by the number of bonding pairs and lone pairs of electrons around the central atom, which influence the shape due to repulsion between electron pairs. Understanding molecular geometry is crucial for predicting the physical and chemical properties of substances.

VSEPR Theory

Valence Shell Electron Pair Repulsion (VSEPR) theory is a model used to predict the geometry of individual molecules based on the repulsion between electron pairs in the valence shell of the central atom. According to VSEPR, electron pairs will arrange themselves to minimize repulsion, leading to specific molecular shapes, such as trigonal planar or trigonal pyramidal.

Formal Charge and Ion Stability

Formal charge is a concept used to determine the distribution of electrons in a molecule or ion, helping to assess its stability. In the case of the SO3 molecule and the SO3^2– ion, the formal charge influences the arrangement of electrons and the resulting molecular shape. Understanding formal charge is essential for predicting the behavior of ions and their geometries.

a. Why is the SO3 molecule trigonal planar but the SO32– ion is trigonal pyramidal?