Atom 

Derived from Greek word atomas means indivisble 

Its basic building block of all matters

Consitss of 3 particles : Proton, electron and neutron

Proton : positive charged particle

Electron : negative charged particle

Neutron : Neutral particle

                

ATOMIC STRUCTURES

Structure of atom is replica of our solar system. In solar system sun is present at the center and all the planets revolve around sun in elliptical orbit. Similary atom has a nucleus at centre where as the negative charged particle known as electron revolve around atom in elliptical orbit. Nuclues consits of positive charged paticle proton and neutral charge particle neutrom

ATOMIC NUMBER

Atomic number represents number of protons in an atom. Atomic number of hydrogen is 1(nucleus has 1 proton). Atomic number of helium is 2(nucleus has 2 proton). Number of electrons and protons will equal in an atom, make it neutral

ORBIT SHELL ENERGY LEVEL

The path at which an electron revolves is known as orbit or shells. Shells are named as K,L,M,N,.. orbits are named as first, second, thrid. The K shell or first orbit can hold only 2 electrons. Other shells or orbit can have only 8 electrons even though it can accomodate more number of electrons as per the formula 2*n*n, where n is the order of the orbit.