A question that bugged me the minute i heard the word atom

[stunner5000pt]

i asked my tenth grade teacher this question but he kept chaning the subject!
I am not really familiar with the 'intense' math (im still in my thrid year of undergrad physics) that goes into solid state physics (if this is a question relating to that field of study) so if possible try and explain in layman's terms.
anyway... what gives atoms their properties?
For example why would something like Mercury have such a low melting point but something adjacent to it on the periodic table have a considerably higher melting point? I do know that trends seem to be carried in the columns of the periodic table... but why would something with +/- 1 atomic number have starkly (once again, i m not sure if that is the case) different properties? I mena its only ONE electron and one proton? How could One electron change the structure of some metal for example?

 

[Gokul43201]

For the most part, atomic properties vary only gradually from one group to the next. There are some exceptions to this however (such as, for instance, the MP of Hg). These exceptions typically occur at electronic configurations involving fully or half-filled sub-shells or shells (and it takes only one electron to go from a partly filled subshell to a fully filled subshell).

In the case of the Hg group of elements, the culprit is the fully filled 5d orbitals. This makes Zn, Cd and Hg relatively inert compared to their neighbors. This is exhibited in their very small bond enthalpies in gaseous diatomic species and their large ionization energies, for instance.

 

[Mk]

Chemical properties of atoms are derived from the electron shells, mostly the valance shell, or the electrons with the most energy and are farther away.