Problem 106 - Chemistry Matter and Change

Question

According to the quantum mechanical model of the atom, what happens when an atom absorbs a quantum of energy?

Step-by-Step Solution

Answer

An atom absorbs a photon, causing an electron to move to a higher energy level temporarily.

Step 1: Understanding Quantum Absorption

When an atom absorbs a quantum of energy, also known as a photon, the energy is taken up by one of the atom's electrons, causing it to move to a higher energy level or orbital. This specific jump to a higher state is called an electronic transition.

Step 2: Moving to an Excited State

In the excited state, the electron occupies a higher orbital than in the ground state. This state is less stable compared to the original, or ground, state of the atom.

Step 3: Conservation of Energy

According to the conservation of energy, the energy of the absorbed photon is equal to the energy difference between the initial (ground state) and the final (excited state) energy levels, denoted by ΔE = E_final - E_initial.

Step 4: Temporary State and Subsequent Actions

The excited state is temporary. The electron will usually release the absorbed energy and drop back to its lower energy level (ground state), often emitting a photon in the process.

Key Concepts

Quantum Absorption

Quantum absorption is a fundamental concept in the quantum mechanical model of the atom. Simply put, when an atom absorbs energy in the form of light or another electromagnetic wave, this occurs through a process called quantum absorption. A particular energy packet, known as a photon, is absorbed, resulting in a distinct increase in the energy of the atom. Specifically, this energy is transferred to one of the electrons orbiting the nucleus.
The absorption is not random; only specific amounts of energy are accepted. Each type of atom or molecule has particular energy levels. Thus, only photons with the right amount of energy—matching the difference between these energy levels—can be absorbed by the atom.

• Quantum absorption happens when an electron absorbs a photon.
• This energy must exactly match the energy difference between two levels.
• Quantum absorption leads to a change in the energy state of the electron.

Excited State

After absorbing energy through quantum absorption, the electron isn't just in a random position. It enters a state known as the excited state. An excited state occurs when an electron has absorbed sufficient energy to move from its lowest energy level, or ground state, to a higher energy level.
This higher energy level is less stable. Electrons in the excited state tend to want to return to their previous ground state because that state is more stable energetically. The time an electron stays excited is very short, typically fractions of a second, making this state temporary.

• An excited state is when an electron gains energy and moves to a higher orbital.
• Excited states are always temporary.
• Electrons naturally return to their ground state by releasing energy.

Electronic Transition

Electronic transition describes the movement of an electron from one energy level to another within an atom. When quantum absorption causes an electron to move from a lower energy to a higher energy level, we say that an electronic transition has occurred. The concept of an electronic transition is crucial for understanding how atoms interact with light and other forms of energy.
The transition is akin to jumping from one step on a stairway to another—it’s discrete and well-defined, aligned with the quantized nature of atomic energy levels.

• Electronic transitions involve the movement of electrons between energy levels.
• They occur due to the absorption or emission of energy.
• These transitions are the basis for many phenomena, such as the emission of light.

Conservation of Energy

The conservation of energy principle is a key aspect in understanding quantum absorption and electronic transitions. This law states that energy cannot be created or destroyed—only transformed from one form to another. In the context of an atom, when a photon of energy is absorbed, the total energy before and after this process must remain constant.
The energy of the absorbed photon equals the difference in energy between the electron's initial energy level and its final energy level (denoted as \( \Delta E = E_{\text{final}} - E_{\text{initial}} \)). This ensures that no energy is lost or created during the transition.

• Energy conservation means the total energy in a system remains constant.
• The energy absorbed by the electron equals the energy difference between levels.
• Energy conservation governs how and why electrons transition between levels.