Main Difference – Excitation vs Ionization Potential
Excitation and ionization potential are two terms used in chemistry to explain the relationship between electrons and atomic nuclei of chemical elements. Atomic nuclei are composed of protons and neutrons. Hence, they are positively charged. There are electrons in movement around the nucleus along certain energy levels. Electrons are negatively charged. Excitation is the movement of an electron from a lower energy level to a higher energy level by absorbing energy. It makes an atom move from a ground state to an excited state. Ionization energy is the removal of an electron from a neutral gaseous atom. This makes a cation; when an electron is removed, the atom does not have a negative charge to neutralize the positive charge of the atom. The main difference between excitation and ionization potential is that excitation explains the movement of an electron from a lower energy level to a higher energy level whereas ionization potential explains the complete removal of an electron from an energy level.
Key Areas Covered
1. What is Excitation
– Definition, Explanation, Electromagnetic Spectrum
2. What is Ionization Potential
– Definition, First Ionization Energy, Second Ionization Energy
3. What is the Difference Between Excitation and Ionization Potential
– Comparison of Key Differences
Key Terms: Atomic Nuclei, Electromagnetic Spectrum, Electron, Excitation, Excited State, Ground State, Ionization Energy, Ionization Potential
What is Excitation
In chemistry, excitation is the addition of a discrete amount of energy to a system such as an atomic nucleus, an atom or a molecule. Excitation causes the change of the energy of the system from a ground energy state to an excited energy state.
The excited states of systems have discrete values rather than a distribution of energies. This is because excitation occurs only when an atom (or any other system mentioned above) absorbs a certain portion of energy. For example, in order to make an electron move to an excited state, the amount of energy that should be given is equal to the energy difference between the ground state and the excited state. If the given energy is not equal to this energy difference excitation does not occur.
Same as for electrons, protons and neutrons in atomic nuclei can be excited when they are given the required amount of energy. But the energy required to make the nucleus move to an excited state is very high when compared to that of electrons.
A system does not remain in the excited state for a long time since an excited state having a high energy is not stable. Therefore, the system needs to release this energy and come back to the ground state. The energy is released in the form of emission of quantum energy, as photons. It occurs usually in the form of visible light or gamma radiation. This return is called decay. Decay is the inverse of excitation.
Electromagnetic Spectrum
Figure 1: Electromagnetic Spectrum of Hydrogen
When an electron has absorbed energy and comes to an excited state, it returns to its ground state by emitting the same amount of energy. This emitted energy leads to the formation of an electromagnetic spectrum. The electromagnetic spectrum is a series of lines. Each line indicates the energy emitted when returning to the ground state.
What is Ionization Potential
Ionization potential or ionization energy is the amount of energy required to remove the most loosely bound electron from a neutral, gaseous atom. This electron is a valence electron because it is the electron that resides farthest from the atomic nucleus. The ionization of a neutral atom causes the formation of a cation.
The removal of this electron is an endothermic process, in which energy is absorbed from the outside. Therefore, the ionization potential is a positive value. In general, closer the electron to the atomic nucleus, higher the ionization potential.
For elements in the periodic table, there are ionization potentials given as first ionization energy, second ionization energy, third ionization energy and so on. First ionization energy is the amount of energy required to remove an electron from a neutral gaseous atom, forming a cation. Second ionization energy of that atom is the amount of energy required to remove an electron from the cation formed after first ionization.
Figure 2: First Ionization Energy Variations in Periodic Table
In general, ionization energy decreases down the group of the periodic table. This is due to the increase in atomic size. When the atomic size increases, the attraction to the farthest electron from atomic nucleus decreases. Then it is easy to remove that electron. Hence, a less energy is required, resulting in a decreased ionization potential.
But when going from left to right along a period of the periodic table, there is a pattern of ionization energy. The ionization energies vary based on the electronic configuration of elements. For example, the ionization energy of group 2 elements is higher than that of group 1 elements and group 3 elements as well.
Difference Between Excitation and Ionization Potential
Definition
Excitation: Excitation is the addition of a discrete amount of energy to a system such as an atomic nucleus, an atom or a molecule.
Ionization Potential: Ionization potential is the amount of energy required to remove the most loosely bound electron from a neutral, gaseous atom.
Purpose
Excitation: Excitation explains the movement of an electron from a lower energy level to a higher energy level.
Ionization Potential: Ionization potential explains the removal of an electron from an energy level completely.
Energy Change
Excitation: Excitation requires energy from outside, but this energy is soon released as photons.
Ionization Potential: Ionization potential is the amount of energy absorbed by an atom, and it is not released again.
End Product Stability
Excitation: Excitation forms an excited state which is unstable and has a short lifetime.
Ionization Potential: Ionization potential forms a cation which most of the times is stable after removal of an electron.
Conclusion
Excitation and ionization potential in chemistry are two terms used to explain the relationship between energy changes and atomic behavior of chemical elements. The main difference between excitation and ionization potential is that excitation explains the movement of an electron from a lower energy level to a higher energy level whereas ionization potential explains the complete removal of an electron from an energy level.
Reference:
1. “Excitation.” Encyclopædia Britannica, Encyclopædia Britannica, inc., 17 Aug. 2006, Available here.
2. “Excited state.” Wikipedia, Wikimedia Foundation, 22 Jan. 2018, Available here.
3. “Ionization Energies.” Ionization Energy, Available here.
Image Courtesy:
1. “Hydrogen spectrum” By OrangeDog – Own work by uploader. A logarithmic plot of λ for , where n′ ranges from 1 to 6, n ranges from n′ + 1 to , and R is the w:Rydberg constant (CC BY-SA 3.0) via Commons Wikimedia
2. “First Ionization Energy” By Sponk (PNG file)Glrx (SVG file)Wylve (zh-Hans, zh-Hant)Palosirkka (fi)Michel Djerzinski (vi)TFerenczy (cz)Obsuser (sr-EC, sr-EL, hr, bs, sh)DePiep (elements 104–108)Bob Saint Clar (fr)Shizhao (zh-Hans)Wiki LIC (es)Agung karjono (id)Szaszicska (hu) – Own work based on: Erste Ionisierungsenergie PSE color coded.png by Sponk (CC BY 3.0) via Commons Wikimedia
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