What is Energy State?

The energy state is also familiarly known as the energy level plays a vital role in explaining the atomic structure. The energy levels or the energy state is any discrete (definite) value from a set of values of total energy for a subatomic particle confined by a force to limited space or for a system of such particles, for example like an atom or a nucleus. The energy level is an old name used with the electron orbits of the Bohr model before quantum mechanics. In the quantum mechanical treatment and because of the uncertainty principle, thus we can not have orbits and hence the term energy states are used instead, thus technically there is not much of a difference between energy levels and energy states.

According to the photoelectric effect, we know that any electron striking on a metal surface can absorb the energy of one photon. In other words, an electron can absorb energy equal to h𝜈. An atom consists of a nucleus and free electrons revolving around the nucleus in discrete orbits. These valence electrons transition will cause different energy levels depending on the amount of energy being absorbed. In this article, we will have a deep insight into what is an energy state, energy levels, and its importance in understanding the atomic structures.


Energy Level

Let us have a look at the energy level with a simple illustration. Consider a positively charged nucleus such that an electron is revolving around it in its outermost orbital or shell. A photon is striking the electron and as a matter of fact, the electron will absorb the photon. As a result of the absorption of a photon by an electron one of the two things will occur:

  1. If the electron acquires more energy after absorption of a photon, then the electron will get excited and thus it will jump to a shell that is further away from the nucleus. That implies the electron is gone up by an energy level and this process is known as the excitation.

  2. If the electron was priorly having sufficient amount of energy to jump from present shell to another and as a result of absorption of photon electron will get furthermore energised in such a way that it will get away from shell or it gets removed from the energy level. This process is known as Ionisation. Basically, ionisation is a process in which when an electron is supplied with enough energy in such a way that it completely gets away from the atom and hence an ion will be created. The removal electron is known as ionization.

But the excited electrons will not stay in the excited energy level for a longer time, eventually, they will try to get back to their original state by de-excitation process. The electrons will lose their energy and transit back to the original state. Every transited level will be having a fixed value and these levels are generally known as the energy levels or the energy states.


What is an Energy Level?

Now, the question that arose is what is an energy level? Let us have a look at the actual meaning of the energy states and what is an energy level is. So, consider an atom with a nucleus and an electron is revolving around the nucleus in the specific shell or it can be anywhere above the considered shell depending upon the energy carried out by the electron itself and these energy levels are very particular for every atom. If we have a closer look at the shell where the electron is located and the levels above it, we observe a set of horizontal lines with definition spacing between them.

Energy levels (also called electron shells) are fixed distances from the nucleus of an atom where electrons can be located. Electrons are considerably small negatively charged particles in an atom that move around the positive nucleus at the centre. Energy level or the energy states are a little like the increments or steps of a staircase. You can stand on one particular step or another but can not stand in between the steps. The same goes for electrons. They can occupy only one energy level or another but not the space between energy levels.

A specific energy level corresponds to a specific value of n, in other words, all the energy levels are quantised in nature. For different integral values of n, we get different discrete energy levels. On the other hand, each discrete set of the four quantum numbers, i.e. {n, l, ml, mS}, designates each energy state. Let’s have a simple example to make these concepts more clear. Now, for n=2 energy level, we get eight distinct energy levels. But all these eight energy states or energy levels have the same value of the total energy because the total energy, as already stated, depends only on the principal quantum number n. Such types of distinct energy states having identical total energy are known as degenerate states and it is said that the energy level n = 2 is 8-fold degenerate. Similarly, we can prove that n = 3 energy level is 18-fold degenerate.


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Thus, Energy states (also known as the electron shells) are just fixed distances from the nucleus of an atom where the electron density is more. As we move farther away from the nucleus, electrons at higher energy (excited states) levels have more energy. Electrons are always added to the most possible lowest energy level first until it has the maximum number of possible electrons, and then electrons are added to the immediate next higher energy level until that level is full, and the process goes on. The maximum number of electrons at a given energy state depends on its number of orbitals. There are at most two electrons per orbital. Electrons in the outermost energy state of an atom are called valence electrons. They are helpful in determining many of the properties of an atom, including how reactive it is.


Did You Know?

One of the important concepts regarding energy levels is that with classical potentials, the potential energy is usually set to zero at infinity, leading to negative potential energy for bound electron states. This is found to be helpful in determining the many intrinsic properties of an atom.

FAQs (Frequently Asked Questions)

1. What is the Difference Between Energy Level and the Energy State?

Ans: There is no difference between energy levels and energy state, perhaps both mean the same. But, the energy level is an old name used with the electron orbits of the Bohr model before quantum mechanics. In the quantum mechanical treatment and because of the uncertainty principle, thus we can not have orbits and hence the term energy states are used instead, thus technically there is no major difference between energy levels and energy states.

2. What is the Allowed Energy State?

Ans: Allowed energies are determined by the principal quantum number (n), with n increasing as energy increases.