Energy levels for an electron in an atom: ground state and excited states. After absorbing energy, an electron may "jump" from the ground state to a higher energy excited state.
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A quantum mechanical system or particle that is bound—that is, confined spatially—can only take on certain discrete values of energy, called energy levels. This contrasts with classical particles, which can have any amount of energy. The term is commonly used for the energy levels of the electrons in atoms, ions, or molecules, which are bound by the electric field of the nucleus, but can also refer to energy levels of nuclei or vibrational or rotational energy levels in molecules. The energy spectrum of a system with such discrete energy levels is said to be quantized.
In chemistry and atomic physics, an electron shell, or principal energy level, may be thought of as the orbit of one or more electrons around an atom's nucleus. The closest shell to the nucleus is called the "1 shell" (also called "K shell"), followed by the "2 shell" (or "L shell"), then the "3 shell" (or "M shell"), and so on farther and farther from the nucleus. The shells correspond with the principal quantum numbers (n = 1, 2, 3, 4 ...) or are labeled alphabetically with letters used in the X-ray notation (K, L, M, N...).
Each shell can contain only a fixed number of electrons: The first shell can hold up to two electrons, the second shell can hold up to eight (2 + 6) electrons, the third shell can hold up to 18 (2 + 6 + 10) and so on. The general formula is that the nth shell can in principle hold up to 2n2 electrons.[1] Since electrons are electrically attracted to the nucleus, an atom's electrons will generally occupy outer shells only if the more inner shells have already been completely filled by other electrons. However, this is not a strict requirement: atoms may have two or even three incomplete outer shells. (See Madelung rule for more details.) For an explanation of why electrons exist in these shells see electron configuration.[2]
If the potential energy is set to zero at infinite distance from the atomic nucleus or molecule, the usual convention, then bound electron states have negative potential energy.
If an atom, ion, or molecule is at the lowest possible energy level, it and its electrons are said to be in the ground state. If it is at a higher energy level, it is said to be excited, or any electrons that have higher energy than the ground state are excited. An energy level is regarded as degenerate if there is more than one measurable quantum mechanical state associated with it.
^Re: Why do electron shells have set limits ? madsci.org, 17 March 1999, Dan Berger, Faculty Chemistry/Science, Bluffton College
^Electron Subshells. Corrosion Source. Retrieved on 1 December 2011.
energy, called energylevels. This contrasts with classical particles, which can have any amount of energy. The term is commonly used for the energy levels...
In quantum mechanics, an energylevel is degenerate if it corresponds to two or more different measurable states of a quantum system. Conversely, two or...
state physics to analyze the energylevels in a solid, the Fermi level can be considered to be a hypothetical energylevel of an electron, such that at...
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and in the form of heat and light. Energy is a conserved quantity—the law of conservation of energy states that energy can be converted in form, but not...
corresponding to a kinetic energy), whereas the Fermi level is a total energylevel including kinetic energy and potential energy. The Fermi energy can only be defined...
using the below description of the rotational energylevels. While the study of vibrational energylevel of the diatomic molecules can be described using...
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of a solid describes the range of energylevels that electrons may have within it, as well as the ranges of energy that they may not have (called band...
typically at a lower energylevel than its unbound constituents. According to relativity theory, a ΔE decrease in the total energy of a system is accompanied...
neon. However, transition elements have (n−1)d energylevels that are very close in energy to the ns level. So as opposed to main-group elements, a valence...
still commonly taught to introduce students to quantum mechanics or energylevel diagrams before moving on to the more accurate, but more complex, valence...
spectrum. In addition to the electronic energylevels shared with atoms, molecules have additional quantized energylevels corresponding to vibrational and rotational...
sound energy density: P = A c w , {\displaystyle P=Acw,} where c stands for the speed of sound; w stands for the sound energy density. Sound power level (SWL)...
matter on an atomic level. Quantum effects provide additional sources of EMR, such as the transition of electrons to lower energylevels in an atom and black-body...
The particle may only occupy certain positive energylevels. Likewise, it can never have zero energy, meaning that the particle can never "sit still"...
spectral lines are due to the electron making transitions between two energylevels in an atom. The classification of the series by the Rydberg formula...
matching energylevel. For this to occur, the electron must drop to a lower energy state that has an energy difference matching the energy of the interacting...
band diagram is a diagram plotting various key electron energylevels (Fermi level and nearby energy band edges) as a function of some spatial dimension,...
for the "Protection Levels for Occupants of Logistic and Light Armored Vehicles". The standard covers strikes from kinetic energy, artillery and IED blasts...
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one-dimensional potential energy box is the most mathematically simple example where restraints lead to the quantization of energylevels. The box is defined...
two or three gamma-rays, depending on the relative spin states. The energylevels of the two particles are similar to that of the hydrogen atom (which...
discrete energylevels are equally spaced, unlike in the Bohr model of the atom, or the particle in a box. Third, the lowest achievable energy (the energy of...
During a molecular, atomic or nuclear transition to a lower energylevel, photons of various energy will be emitted, ranging from radio waves to gamma rays...
levelized cost of energy may include the costs of either electricity or heat. The latter is also referred to as levelized cost of heat or levelized cost...
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