Hazardous Chemicals Handbook (pdf) - CCC

22 GENERAL PRINCIPLES OF CHEMISTRY
Table 3.1 Electronic configuration of selected elements
Element Symbol Atomic No. electrons No. electrons No. electrons No. electrons in
(proton) in 1st shell in 2nd shell in 3rd shell 4th shell
number
Hydrogen H 1 1
Helium He 2 2
Lithium Li 3 2 1
Beryllium Be 4 2 2
Boron B 5 2 3
Carbon C 6 2 4
Nitrogen N 7 2 5
Oxygen O 8 2 6
Fluorine F 9 2 7
Neon Ne 10 2 8
Sodium Na 11 2 8 1
Magnesium Mg 12 2 8 2
Aluminium Al 13 2 8 3
Silicon Si 14 2 8 4
Phosphorus P 15 2 8 5
Sulphur S 16 2 8 6
Chlorine Cl 17 2 8 7
Argon Ar 18 2 8 8
Potassium K 19 2 8 8 1
Calcium Ca 20 2 8 8 2
Scandium Sc 21 2 8 9 2
Titanium Ti 22 2 8 10 2
Vanadium Va 23 2 8 11 2
Chromium Cr 24 2 8 13 1
Manganese Mn 25 2 8 13 2
between brands. It is possible to isolate the different chemical components from mixtures by
physical means.
Periodic table
The number of protons plus neutrons in an atom is termed the mass number. The number of
protons (which also equals the number of electrons) is the atomic number. When elements are
arranged in order of their atomic numbers and then arranged in rows, with a new row starting after
each noble gas, the scheme is termed the periodic table. A simplified version is shown in Table 3.2.
The following generalizations can be made. Period 2 elements at the top of Groups I to VII
tend to be anomalous. Atomic and ionic radii decrease across a period but increase down a group.
Elements in a period have similar electronic configurations and those in groups have the same
outer electronic arrangements. Elements at the top of a group tend to differ more from the
succeeding elements in the group than they do from one another. Metals are on the left of the table
and non-metals on the right. Elements such as silicon and germanium are borderline. Elements
become less metallic on crossing a period and more metallic on descending a group. The Group
I elements are alkali metals with reactivity increasing from top to bottom of the table. So the
exothermic reaction of potassium (K) with water is more vigorous than that of lithium (Li).
Electronegativities increase across a period to a maximum with Group VII, the halogens, for
which reactivity decreases from top to bottom of the table. Elements in Group 0 are unreactive