TwoOldGuys™ Study Guides
BI-122 Biology
Chemical Basis of Life

basic Chemistry

The chemical behavior of any element is determined by the number, and configuration of its electrons.
Mendeleev found that when the elements are arranged in order by their atomic number, the resulting pattern of chemical properties suggests that the outer most "shell" (a.k.a. energy level, orbital, valence shell) is 'filled' by 8 electrons as 4 paired electrons. He called this the Periodic Table of the Elements.

Periodic Table of the elements
i ii iii iv v vi vii viii
H He
Li Be B C N O F Ne
Na Mg Al Si P S Cl Ar
K Ca Sc Ti V Cr Mn Fe Co Ni Cu Zn Ga Ge As Se Br Kr
Rb Sr Y Zr Nb Mo Tc Ru Rh Pd Ag Cd In Sn Sb Te I Xe
Cs Ba La* Hf Ta W Re Os Ir Pt Au Hg Tl Pb Bi Po At Rn
Fr Ra Ac* Rf Ha
*Ce Pr Nd Pm Sm Eu Gd Tb Dy Ho Er Tm Yb Lu
*Th Pa U Np Pu Am Cm Bk Cf Es Fm Md No Lr

Most Periodic Tables now include additional information [for example Carbon]:

atomic mass symbol charge
atomic number number of atoms

for example Carbon:

12 C 0
6 1



Valence electrons

Chemical Bonds
covalent . strongest
polar covalent . .
ionic . .
hydrogen . weakest



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revised 19 aug 2006