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Valence electron

    == Definiton ==
    In chemistry valence electrons are the electrons located within the outermost energy level of an atom These electrons participate chemical reactions

    Determinging the Number of Valence Elections

    To determine the quantity of valence electrons an element has you must look at the family (vertical column) in which the element is categorized With the exception of families 3 - 12 (Transition Metals) the number within the units place identifies how many valence electrons are contained within the elements listed under that particular column
    Family Quantity of Valence Electrons
    Family One (Alkali Metals) One
    Family Two (Alkaline Earth Metals) Two
    Famlies Three - Twelve (Transition Metals) One - Two
    Family Thirteen (Boron Group) Three
    Family Fourteen (Carbon Group) Four
    Family Fifteen (Nitrogen Group) Five
    Family Sixteen (Oxygen Group) Six
    Family Seventeen (Halogens) Seven
    Family Eightteen (Noble Gases) *Eight

    The asterisk (*) is used to indicate that all of the noble gases contain eight valence electrons with the exception of helium (He) which only contains two

    Valence Electrons in Chemical Reactions

    The chemical behavior of atoms is largely due to interactions between electrons Electrons of an atom remain within certain predictable electron configurations Electrons fall into shell based on their relative energy level which is usually visualized as their mean distance from the nucleus The electrons in the outermost shell called the valence electrons have the greatest influence on chemical behavior Core electrons (those not in the outer shell) play a role but it is usually in terms of a secondary effect due to screening of the positive charge in the atomic nucleus
    wavefunctions of hydrogen hydrogen] The principal quantum number is at the right of each row and the azimuthal quantum number is denoted by letter at top of each column
    Each shell numbered from the one closest to the nucleus (lowest in energy) can hold up to a specific number of electrons due to its differing sublevel and orbital capacity:
    • Shell 1: 2 electron capacity - s sublevel - 1 orbital
    • Shell 2: 8 electron capacity - s and p sublevels - 4 orbitals
    • Shell 3: 18 electron capacity - s p and d sublevels - 9 orbitals
    • Shell 4: 32 electron capacity - s p d and f sublevels - 16 orbitals

    To determine the electron capacity of a shell the formula 2n² is used where n is the shell number or principle quantum number Electrons fill orbitals and shells from the inside out beginning with shell one Whichever occupied shell is currently most outward is the valence shell even if it only has one electron
    The reason why shells fill up in order is that the energy levels of electrons in the innermost shells are significantly lower than the energy levels of electrons in outer shells So if the inner shells were not completely full the electron in an outer shell would quickly "fall" into the inner shell (with the emission of a photon that would carry away the difference in the energy
    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 Group (ie column) 1 elements contain one electron on their outer shell; Group 2, two electrons; Group 3, three electrons; etc As a general rule the fewer electrons in an atom's valence shell the more reactive it is. Group 1 metals are therefore very reactive with caesium rubidium and francium being the most reactive of all metals
    Every atom is much more stable (ie less energetic) with a full valence shell This can be achieved one of two ways: an atom can either share electrons with neighboring atoms (a covalent bond) or it can remove electrons from other atoms (an ionic bond) Another form of ionic bonding involves an atom giving some of its electrons to another atom; this also works because it can end up with a full valence by giving up its entire outer shell By moving electrons the two atoms become linked This is known as chemical bonding and serves to build atoms into molecules or ionic compounds Five major types of bonds exist: