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:
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.
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.
[Image will be uploaded soon]
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 on Energy State
1. What is an energy state in the context of an atom?
An energy state, also known as an energy level, refers to one of the specific, discrete quantities of energy that an electron can possess within an atom. According to quantum mechanics, electrons do not orbit the nucleus at any random distance but are confined to these specific energy levels. Think of them like steps on a staircase; an electron can be on one step or another, but not in between. Each state is defined by a set of quantum numbers.
2. What is the unit used to measure the energy of an atomic energy state?
While the SI unit of energy is the Joule (J), the energy of an atomic state is more commonly expressed in electron-volts (eV). This unit is more convenient for the tiny energy values involved at the atomic scale. One electron-volt (1 eV) is the amount of energy gained by a single electron when it is accelerated through a potential difference of one volt.
3. What is the formula to calculate the energy of an electron in a specific energy state of a hydrogen atom?
For a hydrogen-like atom, the energy (E_n) of an electron in the n-th energy state is given by the Bohr model formula: E_n = -13.6 * (Z^2 / n^2) eV. Here, 'n' is the principal quantum number (n = 1, 2, 3,...), representing the energy level, and 'Z' is the atomic number of the element. For a hydrogen atom, Z=1.
4. Can you provide an example of energy states in a real atom?
The hydrogen atom provides the clearest example. Its single electron normally resides in the lowest energy state, called the ground state (n=1), with an energy of -13.6 eV. If it absorbs energy (e.g., from a photon), it can jump to a higher energy level, or an excited state, such as the n=2 level (-3.4 eV) or the n=3 level (-1.51 eV). It will later return to a lower state by emitting a photon with energy equal to the difference between the levels.
5. Is there a difference between the terms 'energy state' and 'energy level'?
In modern physics, the terms are often used interchangeably, but there's a subtle distinction that is important for a deeper understanding.
- Energy Level: This is an older term from the Bohr model, referring to the total energy associated with a principal quantum number (n). For example, all electrons with n=2 are at the same energy level.
- Energy State: This is a more precise term from quantum mechanics. It refers to a unique configuration defined by all four quantum numbers {n, l, m_l, m_s}. Multiple energy states can have the same energy level.
6. What is the difference between a ground state and an excited state of an atom?
The ground state is the lowest possible energy state of an atom, where all its electrons occupy the lowest available energy levels according to quantum rules. This is the most stable configuration for an atom. An excited state is any energy state with a higher energy than the ground state. An atom enters an excited state when one or more of its electrons absorb energy and jump to a higher, unoccupied energy level. Excited states are unstable, and the electron will quickly fall back to a lower level, emitting the excess energy as light.
7. What happens when an electron moves from a lower energy state to a higher one, and what happens when it returns?
The movement of an electron between energy states involves the absorption or emission of energy, typically in the form of a photon.
- Moving to a Higher State (Excitation): To jump from a lower to a higher energy state, an electron must absorb a precise amount of energy. This energy must exactly match the difference between the two levels. This process is called excitation.
- Returning to a Lower State (De-excitation): An electron in a higher, unstable energy state will eventually fall back to a lower, more stable state. In doing so, it emits the excess energy, usually as a photon of light with a specific frequency and wavelength corresponding to the energy difference.
8. What does it mean when energy states are 'degenerate'?
In quantum mechanics, degenerate energy states are distinct states that, despite having different quantum number configurations, share the exact same energy value. For example, in a hydrogen atom, the energy of a state primarily depends on the principal quantum number 'n'. The n=2 energy level includes multiple orbitals (2s and 2p). All the electron states within these orbitals (a total of 8 distinct states when considering spin) have the same energy. Therefore, the n=2 energy level is said to be 8-fold degenerate.
9. How is an atomic 'energy state' different from a 'state of matter' like solid, liquid, or gas?
These two concepts describe phenomena on completely different scales.
- An atomic energy state is a quantum mechanical property of a single atom, describing the discrete energy an electron can have within that atom. It is about the internal configuration of an atom.
- A state of matter (solid, liquid, gas, plasma) is a macroscopic property of a large collection of atoms or molecules. It describes their collective behaviour, such as their arrangement, spacing, and kinetic energy, which determines the overall physical form of a substance.
