Question

In the Bohr model, what happens when an electron makes a transition between orbits?

Short answer

In the Bohr model, when an electron makes a transition between orbits, it either absorbs or emits a photon of energy that is equal to the difference in energy levels.

Step-by-step solution

Understanding the Bohr Model

In the Bohr model of the hydrogen atom, electrons orbit the nucleus in specific, defined orbits. Each orbit corresponds to a certain energy level. The orbits are often referred to as 'shells' or 'energy levels'.

Electron Transition Between Orbits

When an electron transitions between orbits or energy levels, it either absorbs or emits a photon of energy. If the electron moves to a higher energy level (further from the nucleus), it absorbs energy. Conversely, if it transitions to a lower energy level (closer to the nucleus), it emits energy in the form of a photon.

Quantization of Energy

The energy absorbed or emitted during an electron's transition is not arbitrary; it is quantized. This means the energy corresponds to the difference between the energy levels of the initial and final orbits. The frequencies of the absorbed or emitted photons can be calculated using the relation E = hf, where E is the energy difference, h is Planck's constant, and f is the frequency of the photon.

Key concepts

Quantization of Energy

Imagine that energy behaves much like the coins in your pocket; you can have one penny or two, but not a fraction of a penny. This is the essence of quantization of energy. It essentially means that energy comes in discrete 'packets' rather than being continuous. In the context of the Bohr model, this is crucial to understanding how atoms behave.

Each energy level in an atom is likened to a step on a ladder. An electron can be on one step or another, but not between the steps. The energy difference between steps is fixed, and when an electron jumps from one step to another, it must absorb or emit a specific amount of energy equal to the difference between these steps. This quantum leap results in the absorption or emission of a photon with energy \( E = h u \) where \( h \) is Planck's constant and \( u \) is the frequency of the photon.

• The energy is quantized, meaning that electrons can only exist at specific energy levels.
• A transition between these levels involves exact and discrete changes in energy.
• This quanta or specific amount of energy is what we observe as characteristic lines in an emission or absorption spectrum.

This understanding replaced the prior classical notion that energy could change smoothly and continuously.

Absorption and Emission of Photons

The colors we see in neon signs and the different lines in a spectral analysis result from the absorption and emission of photons. In the Bohr model, a photon is a quantum of light, a discrete bundle of electromagnetic energy. When an electron absorbs a photon, it gains the photon's energy and moves to a higher, more distant orbit from the nucleus.

Conversely, when an electron loses energy, it emits a photon and falls to a lower orbit closer to the nucleus. This electron behavior is like a dance - a step up in energy requires the electron to take in energy, and a step down requires the release of energy.

• Photon absorption occurs when an electron transitions to a higher energy level.
• Photon emission happens when an electron goes down to a lower energy level.
• The energy of the photon corresponds to the exact energy difference between the two levels involved in the transition.

The concept that energy absorption and emission occur only at specific, quantized energy levels is fundamental for technologies such as lasers and even explains why we see distinct colors in fireworks.

Hydrogen Atom Energy Levels

The simplest atom, hydrogen, serves as a great model system to showcase the principles of quantum mechanics. Hydrogen atom energy levels are critical to understanding electron behavior in quantum theory.

In the Bohr model, hydrogen's lone electron revolves in certain permitted orbits, each with a distinct energy level. These levels are labelled with an integer number, n, known as the principal quantum number. n=1 is the level closest to the nucleus, with the lowest energy, and as n increases, the electron moves further from the nucleus and the energy increases.

• The lowest energy state of the atom is called the ground state.
• As the principal quantum number, n, increases, the electron’s energy level increases.
• Energy level transitions produce spectral lines specific to hydrogen, visible in its emission or absorption spectrum.

Understanding these energy levels helps in fields ranging from astrophysics, where hydrogen's spectral lines serve as cosmic fingerprints, to medicine, with techniques like MRI using principles of quantum mechanics to diagnose conditions.