Red = electro positivity Blue = Electro negativity.

Fig.2. The  elements of the first 3 periods of  Periodic Table.

In this section of the Periodic Table, ( Atomic numbers 1 to 18 )  it is possible to observe some of the magical features.  

Mendeleev , in 1869,  without an idea of the internal structure of the atom,  (even the plum pudding model was proposed in 1904)  simply using only the properties of elements figured out the Periodic Table.

This most amazing structure has become an encyclopedia for chemistry.

In science, a Theory or a Law,  generally corrodes with time.   The Periodic Table has got highly polished and glitters in the light of modern technology.

In  Fig 2. The columns  are the groups  according to the number of electrons in the outer shell (shown by dots.  The horizontal rows are periods according to the number of orbits shown in black circles. The atomic number given for each element is equal to the number of positive charges, protons. In the nucleus.

All the properties of each element can be explained according to the electrical charges inside the atoms.  Those shaded in red have less than 4 e –  in their outer shells.  They  can shed  e – to  get the structure of an inert gas.

Taking examples from group 1  and 2 we get:-

1. H  -   e –  = H e +     ( Similar to Helium)

2. Na - e –    =  Na +     (Similar to Neon)

3. Mg - 2 e –     =   Mg ++   (similar to Neon)

The atoms that donate e – to form ions are  metals.  Shaded red.  Darker the colour easier to give e–.. This tendency is described as electropositive.

Those that have an affinity to get e – are in blue.   They are electronegative.

Example:-

• Br  +  e –   = Br +   ( similar to Argon)

( Hydrogen is an exception, It has metallic properties)

Atoms wish to acquire  a  complete outer shell either by accepting or donating electrons.

The periodic table depicts a beautiful gradation of properties.  As you move to the right the affinity for electrons increase. This is due to the increasing number of protons.  Just as the electron number increases the volume of the atom increases due to repulsion.   Group 7 and 8  become gaseous.

As you come down the groups it become easy for them to donate electrons as extra shells are added.

Changing the size along Periods and Groups

Fig. 3   Atomic volume.

Trends in Gropup !A and 2 A.

Trends in Group 1A.