Question

Which electronic level would allow the hydrogen atom to absorb a photon but not to emit a photon? (a) \(1 \mathrm{~s}\) (b) \(2 \mathrm{~s}\) (c) \(2 \mathrm{p}\) (d) \(3 \mathrm{~s}\)

Short answer

The (a) 1s level absorbs but does not emit a photon.

Step-by-step solution

Understanding Absorption and Emission

An atom absorbs a photon when an electron moves to a higher energy level, while it emits a photon when an electron moves to a lower energy level.

Considering the Ground State

In the ground state (1s for hydrogen), the electron is at the lowest energy level and can only absorb a photon to move to a higher state. Emission occurs from excited states moving to lower states.

Evaluating Higher Energy Levels

For levels higher than 1s (2s, 2p, 3s), an electron can either absorb a photon and move to an even higher level or emit a photon to move down.

Selecting the Correct Level

The ground state (1s) allows absorption of a photon to enter an excited state, but there is no lower level for the electron to drop to and emit a photon. Therefore, it can only absorb and not emit.

Key concepts

Photon Absorption

Photon absorption is a fundamental process by which an atom gains energy. When a photon, which is a particle of light, interacts with an atom, it can transfer its energy to an electron in the atom. This added energy allows the electron to move from a lower energy level to a higher one. This process is highly selective; the photon must have an energy exactly equal to the difference between the two energy levels of the electron.

The absorption of photons can bring electrons to increasingly higher energy states. This means that if an atom is in its ground state, the lowest energy state, it can absorb a photon and move the electron to an excited state. Absorption requires the photon's energy to match the gap between the current electron level and a higher level. If the photon's energy doesn't match, it simply passes by without being absorbed.

Here's a summary of photon absorption:

• Photon absorption occurs when the photon's energy matches the energy gap between two electron levels.
• The electron absorbs the photon and moves to a higher energy level.
• Not all photons will be absorbed; they must have the right energy.

Ground State of Hydrogen Atom

The ground state of a hydrogen atom is its most stable and lowest energy configuration. In this state, the electron resides in the 1s orbital, which is the closest orbital to the nucleus of the atom. This is the default state for a hydrogen atom when it is not interacting with any external energy sources, like light or heat.

In this state, the electron is closest to the nucleus, minimizing its potential energy. Since the ground state is the lowest energy state, absorption of a photon can move the electron to a higher energy level. However, since there are no lower states, emission cannot occur from the ground state.

Key points about the ground state of a hydrogen atom include:

• The 1s orbital is the lowest possible energy level.
• Electrons in the ground state can only absorb a photon to transition to an excited state.
• Emissions occur from higher energy levels back to this level, not from the ground state itself.

Excited Energy Levels

When an electron absorbs enough energy from a photon, it can move to what are called excited energy levels. These levels are higher in energy than the atom's ground state. In hydrogen, these excited states correspond to orbitals such as 2s, 2p, 3s, and so on.

In excited energy levels, the electron is found further from the nucleus, and this configuration is typically less stable compared to the ground state. Excited states are temporary and will often return to a lower energy state by emitting a photon. This emission releases energy equal to the difference between the two involved energy levels.

Key characteristics of excited energy levels include:

• Electrons in an excited state can emit photons to drop to lower energy levels.
• Excited states provide more versatility for energy absorption and emission.
• These states are pivotal in explaining phenomena such as spectral lines in hydrogen.