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6_Energy levels.html
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<p class="head">Energy Levels</p>
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<p><a class="black" href="https://cvertan.github.io/physics4dh.github.io/5_Atom.html" target="frameterms">Electrons</a> revolve around the <a class="black" href="https://cvertan.github.io/physics4dh.github.io/5_Atom.html" target="frameterms">nucleus</a> in an <a class="black" href="https://cvertan.github.io/physics4dh.github.io/5_Atom.html" target="frameterms">atom</a> at different orbits. Each orbit has a unique <a class="black" href="https://cvertan.github.io/physics4dh.github.io/20_Energy.html" target="frameterms">energy</a>. Certain discrete values of energy are called <a class="def">energy levels</a>. The electrons orbiting at a larger distance from the nucleus have higher energy (are at higher energy level) whereas the electrons orbiting at a smaller distance from the nucleus have lower energy (are at lower energy level). </p>
<p>An energy level of the electron with the lowest energy is the <a class="def">ground level</a> (or <a class="def">ground state</a>) of the electron. All other energy levels with higher energies are called <a class="def">excited levels</a> (or <a class="def">excited state</a>). The electron being in the excited state is called <a class="def">excited electron</a> or “electron is excited”. When an electron in an atom is in an excited state, then the whole atom is in an excited state. An atom is said to be in a ground state only if all its electrons are in ground states.</p>
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<div class="desc">Ground and excited energy states of electron in an atom.</div>
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<p>Under normal conditions (in the absence of external influences) an electron cannot stay in an excited state for a long time and will always tend to move to the ground or lower levels, what is determined by the laws of physics. The average time up to which an electron can stay at higher energy level is called <a class="def">lifetime of an electron</a> on the certain excited energy level. Usually, the lifetime of electrons in excited state is very short ranging between 10<a class ="super">-8</a> and 10<a class ="super">-3</a> s.</p>
<p>After completing its lifetime, the electron returns to the lower state. Transition of the electron from the excited state to lower state can result in the release of a <a class="black" href="https://cvertan.github.io/physics4dh.github.io/2_Photon.html" target="frameterms">photon</a>. In this case, the transition of the electron is called <a class="def">radiative</a> and the process of releasing a photon is called <a class="black" href="https://cvertan.github.io/physics4dh.github.io/8_Emission.html" target="frameterms">spontaneous emission</a>. <a class="def">Non-radiative</a> transitions of electron between energy levels without the emission of photon are also possible.</p>
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