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Chapter 12: Problem 10

What does it mean to say that a molecule is in an excited state?

Short Answer

Expert verified
When a molecule is in an 'excited state', it means that one or more of its electrons have absorbed energy and moved to a higher energy level. This is a less common state than the 'ground state', and typically a molecule will return to its ground state by emitting the extra energy.

Step by step solution

01

Define ground state

In chemistry, when a molecule is in its 'ground state', it means that all the electrons are in the lowest available energy levels. This is usually the most stable and common state for a molecule.
02

Define the excited state

When a molecule is in an 'excited state', it means that one or more electrons have absorbed enough energy to move to a higher energy level. This is a less stable state. The added energy can come from various sources including heat, light, or chemical reactions.
03

Explanation of transition

Usually, a molecule in an excited state will return to its ground state by emitting the absorbed energy, often in the form of light (which can be specific wavelengths or colors depending on the energy difference). This is how we get phenomena like neon lights or glow-in-the-dark materials.

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Key Concepts

These are the key concepts you need to understand to accurately answer the question.

Ground State
The ground state of a molecule is like its comfortable resting position. It's the place where all electrons are at their lowest possible energy levels. Think of it like electrons being cozy in the lowest spots available, as they prefer staying in the most stable positions.
This is the most common state for a molecule because it doesn't require additional energy 鈥� everything is calm and steady.
  • All electrons are in the lowest energy levels.
  • This state is stable and requires no extra energy.
  • Most molecules naturally stay in this state.
Understanding the ground state is crucial, as it sets the baseline for learning about excited states and electron transitions. Knowing that molecules prefer the ground state helps us grasp why changes occur when energy is absorbed.
Energy Levels
Energy levels in atoms or molecules can be visualized as the different floors of a building, where electrons reside. The lower floors represent lower energy levels, and the higher floors, higher levels. Electrons naturally prefer the lower floors or levels, just like in the ground state.
  • Each electron corresponds to a specific energy level.
  • The levels are distinct; electrons need a precise energy amount to move between them.
  • Higher energy levels mean less stability.
Energy levels play a key role in chemical reactions and behaviors of electrons within a molecule. They help us understand why electrons jump to higher levels and how molecules enter different states, influencing phenomena like color emission in certain materials.
Electron Transition
Electron transitions happen when electrons absorb or emit energy, causing them to shift between energy levels. Imagine climbing stairs: if you want to move to a higher stair, you need enough energy; similarly, electrons need energy to move to a higher energy level.
When a molecule is exposed to energy (from light, heat, etc.), electrons can jump to a higher level, putting the molecule in an excited state. This is less stable than the ground state.
  • Occurs when electrons absorb or release energy.
  • Transitions to higher energy levels make molecules less stable.
  • Returning to the ground state releases energy, often as light.
Understanding electron transitions explains how substances emit light and why they change appearance. It's a fundamental concept that helps us grasp molecular behavior in various conditions.

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Most popular questions from this chapter

Discuss the statement that the interatomic force law must be attractive to permit condensed phases and must be repulsive to avoid zero volume.

Show that the ratio \(R\) of the total number of molecules in all excited vibrational states to the number in the ground vibrational state is $$ R=\left(e^{h v_{0} / k T}-1\right)^{-1} $$ provided that the levels are assumed to be equally spaced.

From the value \(2940.8 \mathrm{~cm}^{-1}\) for the reciprocal wavelength equivalent to the fundamental vibration of a molecule \(\mathrm{Cl}_{2}\), each of whose atoms has an atomic weight 35 , determine the corresponding reciprocal wavelength for \(\mathrm{Cl}_{2}\) in which one atom has atomic weight 35 and the other 37 . What is the separation of spectral lines, in reciprocal wavelengths, due to this isotope effect?

(a) Specify the resolution, \(\Delta \lambda / \lambda\), of a spectrometer which can just resolve the rotational spectra of \(\mathrm{Na}^{23} \mathrm{Cl}^{35}\) and \(\mathrm{Na}^{23} \mathrm{Cl}^{37}\) assuming \(R_{0}\) to be the same for both molecules. (b) Would this spectrometer also resolve the vibrational spectra of the two molecules, assuming the force constants are the same?

(a) Show that the ratio of the number of molecules in rotational level \(r\) to the number in the \(r=0\) level, in a sample at thermal equilibrium, is a maximum for the level specified by $$ r=\left(k T I / \hbar^{2}\right)^{1 / 2}-1 / 2 $$ (b) For HCl, what is the most populated level at \(600^{\circ} \mathrm{K}\) ?
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