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( Valence electron)
In science, valence electrons are the electrons contained in the outermost, or valence, electron shell of an atom. Valence electrons are important in determining how an element reacts chemically with other elements The fewer valence electrons an atom holds, the less stable it becomes and the more likely it is to react. The reverse is also true, the more full/complete the valence shell is with valence electrons, the more inert an atom is and the less likely it is to chemically react with other chemical elements or with chemical elements of its own type. This is because it takes more transfer of energy (photons) to lose or gain an electron from or into a shell when that shell is more complete/full. Valence electrons have the ability like electrons in inner shells to absorb or release energy (photons). This gain or loss of energy can trigger an electron to move/jump to another shell or even break free from the atom and its valence shell. When an electron absorbs/gains more energy (photons), then it moves to a more outer shell depending on the amount of energy the electron contains and has gained due to the absorption of 1 or more photons. (Also see electrons in an excited state)
When an electron releases/loses energy(photons), then it moves to a more inner shell depending on the amount of energy the electron contains and has lost due to the release of 1 or more photons. The number of valence electrons of an element is determined by its periodic table group (vertical column) in which the element is categorized. With the exception of groups 3–12 (transition metals), the number within the unit's place identifies how many valence electrons are contained within the elements listed under that particular column. The number of electrons in an atom's outermost valence shell governs its bonding behavior. Therefore, elements with the same number of valence electrons are grouped together in the periodic table of the elements. As a general rule, the fewer electrons in an atom's valence shell, the more reactive it is. Group 1 alkali metals are therefore very reactive, with lithium, sodium, and potassium being the most reactive of all metals.
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