Limitations of valence bond theory:

Lack of quantitative predictions:
Valence bond theory does not provide quantitative predictions of bond lengths, bond angles, and other properties. It only provides qualitative explanations for the formation of covalent bonds. This limitation makes it difficult to compare with experimental data and make accurate predictions.

Difficulty in dealing with resonance and delocalization:
Valence bond theory struggles to explain the phenomenon of resonance and delocalization of electrons. It fails to account for the multiple resonance structures and the delocalization of electrons across different atoms. These concepts are better explained by molecular orbital theory.

Overlapping atomic orbitals:
Valence bond theory assumes that covalent bonds are formed by the overlapping of atomic orbitals. However, it does not provide a clear explanation of how atomic orbitals overlap and which orbitals are involved in bonding. This limitation restricts the theory's ability to accurately describe the geometry and bonding in complex molecules.

Difficulty in describing excited states and bond dissociation:
Valence bond theory primarily focuses on the ground state of molecules and struggles to describe excited states and bond dissociation. It fails to explain the behavior of molecules under different energy conditions, limiting its applicability to certain chemical reactions.

Weakness in predicting magnetic properties:
Valence bond theory does not provide a satisfactory explanation for the magnetic properties of molecules. It cannot accurately predict whether a molecule will be paramagnetic or diamagnetic, as it does not consider the concept of molecular orbitals and their spin properties.

Dependence on empirical parameters:
Valence bond theory often relies on empirical parameters to explain certain phenomena. This dependence on empirical data makes it less rigorous and limits its ability to provide a comprehensive understanding of chemical bonding.

Lack of mathematical rigor:
Valence bond theory lacks the mathematical rigor and formalism of other theories such as molecular orbital theory. It relies more on qualitative reasoning and visual representations, which may not be sufficient for a complete understanding of chemical bonding.

In conclusion, while valence bond theory provides a useful qualitative framework for understanding covalent bonding, it has several limitations in terms of quantitative predictions, resonance and delocalization, treatment of excited states and bond dissociation, prediction of magnetic properties, reliance on empirical parameters, and mathematical rigor. These limitations highlight the need for more comprehensive theories like molecular orbital theory to fully understand chemical bonding.