# What is an Energy Level of an Atom? - Definition & Equation

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• 0:03 The Bohr Atomic Model:…
• 1:46 Emission of Light and…
• 3:17 Emission Spectra of…
• 3:58 Lesson Summary

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Lesson Transcript
Instructor: Alfonso Reina
In this lesson, you will learn about the possible energy states that an electron can have in an atom. You will also understand how these energy levels give rise to the light emission spectra of individual atoms.

## The Bohr Atomic Model: Electron Energy Levels

At the beginning of this century, it was already known that atoms were made of protons at the center (the nucleus) and electrons orbiting around them. Scientists later realized that the light emitted from a particular type of atom occurred at specific frequencies. That is, the light given off by a collection of atoms in the gas phase could only be of certain colors. To explain this observation, Niels Bohr proposed that electrons inside an atom occupy only certain allowed orbitals with a specific energy. In other words, the energy of an electron in an atom is not continuous, but 'quantized.' The energies corresponding to each of the allowed orbitals are called energy levels.

To understand this better, think about a bookshelf. Each shelf contains books just like how each possible orbital in an atom contains electrons. Each shelf is different from the others just like how each orbital represents different energy levels for electrons. An electron can't have an energy value half way between two energy levels in an atom. Similarly, a book cannot be placed half way between consecutive shelves. It can only be placed within one shelf.

Each energy level is labeled with the quantum number n (n=1, 2, 3,...) and the energy of a particular level can be determined by the following:

En=-Rh (1/n^2)

This is where Rh is the Rydberg constant of the element. For the simplest atom, the hydrogen atom, Rh=2.18*10^-18 J.

## Emission of Light and Transitions Between Energy Levels

The electrons of individual atoms can be excited from a lower energy state to a higher energy state as shown in the image below. This happens, for example, when a high voltage is applied through a collection of atoms in the gas phase. However, electrons tend to avoid excited states, so after a short time they transition to a lower energy state called relaxation. Because energy was absorbed to excite the electron, energy has to be emitted after the electron transitions to its initial state. The energy is then released in the form of light (electromagnetic waves). The energy difference between the two energy levels involved in the transition defines the color of the light emitted from the atoms. Each color of light has a particular energy and frequency.

The energy of the light emitted from a particular transition can be calculated in the following way:

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