Structure of an Atom ( Class 9)

You have already studied about the structure of an atom and the various theories associated with it.
John Dalton, Rutherford and JJ Thomson conducted experiments and gave the structure of an atom. J.J. Thomson proposed that electrons are embedded in a positive sphere.
Rutherford’s alpha-particle scattering experiment led to the discovery of the atomic nucleus. Rutherford’s model of the atom proposed that a very tiny nucleus is present inside the atom and electrons revolve around this nucleus. The stability of the atom could not be explained by this model. It was Neils Bohr who explained that stability of an atom was related to attaining the Noble gas state where all the shells of the atom were filled with electrons according to their capacity. This was the electronic configuration and to attain this state atoms either gained or lost energy.
J. Chadwick discovered the presence of neutrons in the nucleus of an atom.
So, the three sub-atomic particles of an atom are: (i) electrons, (ii) protons and (iii) neutrons.

You also know that the metallic character represents a group of chemical properties of elements called metals. Metals lose their electrons rapidly and the tendency of an element to lose electrons and form positive ions (cations) is called electropositive or metallic character. For example,alkali metals ( Na, K ) are the most electropositive elements. They are good reducing agents.

"The tendency of an element to accept electrons to form an anion is called its non-metallic or electronegative character." For example, chlorine, oxygen and phosphorous show greater electronegative or non-metallic character. They are good oxidizing agents.

As I was going through some worksheets, I found this site which gives a good understanding of the concept of bonding, equations and also has some good practice sheets.Please do not go through the sheets related to emperical formulae and mole concept. They are for the next grade.

http://crescentok.com/staff/jaskew/isr/chemistry/class12.htm

Do visit this site and practice the worksheets given in it.