Chemical Reactivity

 General rules:

a)      metal atoms tend to transfer electrons to nonmetals when they react.

b)      nonmetal atoms tend to gain or share electrons when they react.

 c) to determine which metal or nonmetal is more reactive, compare elements within groups or periods (for diagonal predictions use Reactivity Series)

Chemical Reactivity in a given period:

_ For metals in a given period reactivity is determined by the number of electrons that must be transferred to a nonmetal.  Those metals with only 1 outer shell electron will be more reactive than metals with two or more electrons.  It takes less energy to remove one electron (lower first ionization energy).

_ For nonmetals in a given period the greater the number of electrons already in the outer shell the more reactive that element will be.  If a nonmetal has seven outer shell electrons it will only need to gain 1 electron to reach its octet.  This nonmetal will be more reactive than a nonmetal that must gain two or more electrons.

 Summary:  In the same period, it is the number of electrons that chiefly determines reactivity.  The smaller the number of electrons transferred between reacting atoms, the more vigorous the reaction.

 Chemical Reactivity in a given group:

_We already know that the negatively charged electrons are held in orbit by their attraction to the positively charged nucleus.  This force of attraction decreases considerable as the distance from the nucleus increases.  Therefore, electrons that are more distant from the nucleus are held less tightly and are more easily lost that are electrons closer to the nucleus.

_Since the more distant electrons are more easily lost, metals having distant electrons (at the bottom of the group) react readily with other nonmetallic elements.

_ Nonmetals combine chemically by gaining or sharing electrons (from metals or other nonmetallic elements).  Since the attraction for electrons is greater when the atomic radius is small, the closer the outermost orbit (called the valence shell) is to the nucleus of a nonmetal, the more reactive it is.  A small radius means that the nucleus pulls strongly on any electrons near it and strongly desires to fill its outer shell (Octet rule).  The more reactive nonmetals will be found near the top of the group.

 Summary:   In the same group, elements have the same number of outershell electrons and it is the atomic radius which largely determines reactivity.  The larger metals loose outer shell electrons more easily and smaller nonmetals (whose attraction for electrons by the nucleus is greater) are more likely to take electrons away from other metals (or share with other nonmetals).

The Reactivity Series

             By studying replacement reactions we can arrange the metals in decreasing order of reactivity.  The reactivity series list the different metals (and hydrogen) in order of their decreasing tendency to lose electrons in water solutions at specified temperatures.  Hydrogen is on the list because it behaves as though it were a metal in certain reactions.  Metals found above hydrogen will replace hydrogen in acid solutions, while those below will not. 

            As we know the tendency of metals to lose electrons depends chiefly on the nuclear charge and on the atomic radius of the metal atom.  The reactivity series may be used to make reasonable predictions concerning the reactivity of different metals.  According to the table, for example, aluminum will replace mercury in an aqueous solution of a mercury compound.  Silver will not replace tin.

 Li   K   Ba   Sr Ca   Na   Mg   Al  Mn  Zn  Cr   Fe  Cd  Co  Ni  Sn   Pb   *H  Sb  As  Bi   Cu    Ag  Pd  Hg  Pt    Au

Most Reactive -------------------------------------------------------------------------------à  Least Reactive

Page Last Updated: Friday March 02, 2007           Webmaster: Larry Jones                 Pickens County School District