Energy levels – Class 12 | Chapter – 12 | Physics Short Notes Series PDF for NEET & JEE

Energy levels: In atomic physics, energy levels refer to the different quantized energy states that an electron can occupy within an atom. These energy levels are determined by the interactions between the electrons and the positively charged atomic nucleus.

The energy levels in an atom are typically represented as a series of discrete energy states, each with a different energy level. The lowest energy state is called the ground state, while higher energy states are called excited states. The energy levels are quantized, meaning that electrons can only occupy certain discrete energy levels and cannot exist in between these levels.

Equation of Energy levels

The energy levels of the hydrogen atom were given by the formula:

E = -13.6 eV/n2


  • E is the energy of the level,
  • n is a positive integer known as the principal quantum number, and
  • eV is an electron volt, a unit of energy commonly used in atomic physics

Importance of Energy levels

The energy levels of an atom are important because they determine the properties and behavior of the atom. Here are some of the key reasons why energy levels are important in atomic physics:

  • Electronic structure: The energy levels of an atom determine the electronic structure of the atom, which is the arrangement of electrons in the atom’s orbitals. The electronic structure of an atom plays a critical role in determining its chemical properties and reactivity.
  • Spectroscopy: The energy levels of an atom are responsible for the characteristic spectral lines that atoms emit and absorb. By measuring the wavelengths of these lines, scientists can determine the energy levels and electronic structure of the atoms, and use this information to study the properties of atoms and molecules.
  • Chemical bonding: The energy levels of the atoms in a molecule determine how the atoms bond to each other and the resulting chemical properties of the molecule. The distribution of electrons in the different energy levels of the atoms in a molecule determines the molecule’s geometry and stability.
  • Excited states: Excited states are higher energy levels that an atom can occupy when it absorbs energy. The properties of excited states play an important role in processes such as fluorescence and phosphorescence, where an atom emits light after being excited.
  • Quantum mechanics: The energy levels of an atom are a key concept in quantum mechanics, which is the branch of physics that describes the behavior of particles at the atomic and subatomic level. The quantized nature of energy levels is a fundamental aspect of quantum mechanics and has wide-ranging implications in physics, chemistry, and other fields.

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By Team Learning Mantras