Energy Level

Niels Bohr proposed the concept of energy levels in his Bohr’s Atomic Model in 1913. His Hydrogen Model explained the stability of electrons revolving in orbits, called stationary orbits, around the nucleus. The energy level is the distance from the nucleus of an atom to the orbit in which the electrons revolve. An electron requires some energy to move from one energy level to another. They can acquire only one energy level at a time and cannot be found in space between two energy levels. These energy levels are also called electron shells.

Overview of Energy Level

The energy levels are represented by the Principal Quantum Number (n), where n=1,2,3…. and so on. The electrons in an energy level on n = 1 have comparatively less energy than electrons in n = 2. The first energy level can also be expressed as ‘K’, the second as ‘L’, the third as ‘M’, and so on. The electrons from the energy level closer to the nucleus have lesser energy, while the electrons farther from the nucleus have more energy. The electrons present in the outermost shell are known as valence electrons, and the outer shell is called the valence shell. Some fundamental properties of atoms are based on the valence shell electrons.

Importance of Energy Level

The study of energy levels is important for understanding the various chemical properties of an element. It helps in learning the chemical bonding of elements and understanding how molecular orbitals are formed.

Electron And Its Energy State

The electrons can absorb energy and jump from lower energy levels to higher energy levels. The electrons can also jump from higher to lower energy levels by emitting energy. The emission of energy is usually in the form of light. Hence, both of these processes require either emission or absorption of light. The lower energy level is known as the ground state, whereas the higher energy level is known as the excited state of an electron.

Quantum Numbers

An electron can be identified in an atom with the help of these four Quantum numbers: Principal quantum number (n): It tells us about the main shell in which the electron resides and the energy level of an electron. Azimuthal quantum number (l):  It tells us about the number of subshells (s,p,d,f) present in any main shell. It also represents the angular momentum of an electron and the shape of the subshell: l=0 for s, l=1 for p, and l=2 for d. Magnetic quantum number (m):  It tells us about the orbitals and orientation of each subshell. The value of m = -l to +l. The number of orbitals present in each subshell is given as (2l+1). Spin quantum number (s):  It indicates the direction of the spinning of electrons – clockwise or anticlockwise.

Energy Level Diagram

Energy level diagrams tell us that all the orbitals of the same energy level do not have the same energies.

• The orbitals 2s and 2p do not have the same energy as they are not placed together
• Orbitals having low energy are placed closer to the nucleus than the orbital having more energy, like s < p < d
• For energy level 3, 3s < 3p < 3d
• For energy level 4, 4s < 4p < 4d
• The outermost subshell of a lower energy level is more stable than the innermost subshell of a higher energy level

Electronic Configuration And Its Rules

The electronic configuration is the arrangement of electrons in an atom. The electrons are filled inside an atom according to their energy level as: 1s, 2s, 2p, 3s, 3p, 4s, 3d, 4p, 5s, 4d, 5p. The process of filling electrons in an atom and forming its electronic configuration is based on the following rules:

1. Pauli’s exclusion principle: “No two electrons have the same 4 quantum numbers and n,l,m,s”. If two electrons have to occupy the same orbital, they must have opposite spin. It also means that an orbital can be occupied by a maximum of two electrons only.
2. Hund’s rule of maximum multiplicity: “For a given electron configuration, the lowest energy term is the one with the greatest value of spin multiplicity”. It means, initially, only a single electron is filled in an orbital, and only if required, another electron is filled in the same orbital with opposite spin.
3. Aufbau principle: “Orbitals with lower energy are filled before the orbitals with higher energy”. It means that the orbitals with the lower energy are filled with electrons first, and then those with higher energy are filled. Half or fully filled orbitals have less energy than other orbitals; hence, they are more stable. Therefore, the configuration of elements with either half or fully-filled orbitals is different.

Conclusion

Energy levels are an essential part of the structure of an atom. It helps us in determining the electronic configuration of an atom. The energy level closer to the nucleus has lower energy than the energy level away from the nucleus. Understanding the importance of energy level is necessary to comprehend the type of bonding of an element. The three rules must be followed while determining the electronic configuration of an element. The arrangement of orbitals explains a lot about the chemical properties of different atoms.