Question

In what ways do atoms in a diatomic molecule behave as though they were held together by a spring? In what ways is this a poor description of the interaction between the atoms?

Short answer

This assumption leads to harmonic oscillator model. It is a poor description of a diatomic molecule because this model has less accurate results and the two chemically bonded atoms with masses do not behave in the same way as the two masses that are connected by a spring.

Step-by-step solution

Determine the way in which atoms in a diatomic molecule behave

If the two atoms with masses are assumed to be chemically bonded by a perfectly elastic massless spring, the diatomic molecule behaves as a harmonic oscillator model.

Determine the reason why the model is a poor description

The harmonic oscillator model yields less accurate results than the rigid rotator. On a macroscopic level, the two chemically bonded atoms with masses do not behave the same way as the two masses that are connected by a spring. Vibrational motion of diatomic molecule cannot be fully explained by harmonic oscillator model because the atoms act differently at the quantum level.

Therefore, harmonic oscillator model has less accurate results and the two chemically bonded atoms with masses do not behave in the same way as the two masses that are connected by a spring.