Question

If an electron is promoted from \(n=2\) to \(n=5\), as Balmer observed, which of the following possibilities BEST describes the source of the line spectra observed? A. A photon is absorbed. B. A photon is emitted. C. An electron is absorbed. D. An electron is emitted.

Short answer

A. A photon is absorbed.

Step-by-step solution

Understand Energy Levels

The Balmer series describes the electron transitions in a hydrogen atom where electrons move between energy levels. Moving from lower energy level (n=2) to a higher energy level (n=5) requires energy.

Energy Absorption Principle

When an electron transitions to a higher energy level, it needs to absorb energy. This energy is in the form of a photon.

Determine the Correct Answer

Since the electron is moving from a lower energy level (n=2) to a higher one (n=5), it must absorb a photon to gain the necessary energy for this transition.

Review Alternatives

Evaluate the provided options: A photon is absorbed (A), a photon is emitted (B), an electron is absorbed (C), and an electron is emitted (D). Only the absorption of a photon (A) aligns with the described energy transition.

Key concepts

Electron Transitions

When we talk about electron transitions, we are referring to the movement of electrons between different energy levels within an atom. These transitions occur when an electron gains or loses energy.
For instance:

• If an electron absorbs energy, it moves to a higher energy level (further from the nucleus).
• If an electron loses energy, it moves to a lower energy level (closer to the nucleus).

The Balmer series specifically deals with electron transitions in a hydrogen atom. It typically involves electrons moving from higher energy levels (=3, 4, 5, etc.) to =2, emitting visible light in the process. However, for an electron to get to these higher energy levels in the first place, it must absorb energy, usually in the form of a photon.

Energy Levels

In an atom, electrons reside in specific regions called energy levels. These are like layers or shells around the nucleus of an atom. Each energy level has a specific energy associated with it:

• Lower energy levels are closer to the nucleus.
• Higher energy levels are further away from the nucleus.

Each electron transition involves a change in energy levels. When moving to a higher energy level, the electron must gain energy. Conversely, when moving to a lower energy level, the electron releases energy. This change in energy is quantified by the difference in energy between the two levels. Understanding energy levels is crucial for explaining electron transitions and photon interactions.

Photon Absorption

Photon absorption is a process where an electron takes in a photon, a particle of light, to gain energy. This absorbed energy propels the electron to a higher energy level. Using our example, if an electron in a hydrogen atom transitions from =2 to =5, it means the electron absorbs a photon with the right amount of energy.
Key points to remember about photon absorption include:

• The energy of the photon must match the energy gap between the two levels.
• Photon absorption results in an increase in the electron's energy.

This concept is important for understanding phenomena like line spectra. In line spectra, each absorbed photon leaves a dark line in the spectrum of light because that specific energy is missing. This is a direct result of the energy transition of the electron.