The chemical properties of each element are determined by the number of electrons in the outermost shell which is called the valence shell. As a rule, atoms of two or more different elements will preferentially link together to form stable compounds when they can share a total of 8 electrons in their outermost (valence) shells.
For example hydrogen (H) has only one electron so it is normally linked to another H atom making a stable molecule (H2). If one of these meets an unaccompanied oxygen atom (O) which has 6 valence electrons, it links to it to form H2O releasing a burst of energy as it burns. The water molecule has a total of 8 electrons in the combined valence shells.
Sodium (1 electron) and chlorine (7 electrons) combine readily to form common salt.
Carbon (4 electrons in the outer shell) combines with four hydrogen atoms to make methane (sharing 8 electrons in their outer shells).
Helium with only 2 electrons and elements that have 8 electrons in the outer shell (neon, argon, krypton, xenon and radon) do not combine with other elements. They are chemically inert.
Element Shell number % of human body mass
1 2 3 4 5
1 hydrogen H 1 - - - - 9.5
2 helium He 2 - - - -
3 lithium Li 2 1 - - - trace
4 beryllium Be 2 2 - - -
5 boron Bo 2 3 - - -
6 carbon C 2 4 - - - 18.5
7 nitrogen N 2 5 - - - 3.2
8 oxygen O 2 6 - - - 65.0
9 fluorine F 2 7 - - - trace
10 neon Ne 2 8 - - -
11 sodium Na 2 8 1 - - 0.2
12 magnesium Mg 2 8 2 - - 0.1
13 aluminum Al 2 8 3 - -
14 silicon Si 2 8 4 - -
15 phosphorus P 2 8 5 - - 1.0
16 sulphur S 2 8 6 - - 0.3
YOU ARE READING
Supernovae and Life
Non-FictionSpace and time began about 13.7 billion years ago but it consisted almost exclusively of hydrogen until some stars grew sufficiently massive to create the heavier elements in gigantic explosions called supernovae. The Sun formed about 4.6 billion...
Part 5 - Carbon
Start from the beginning
