Atom is an indivisible and tiny particle.According to RUTHERFORD, an atom mainly contains two parts.
The central part of the atom is known as nucleus.
It possesses net positive charge.
Its radius is 10-8 cm.
It consists of two charged particles.They are 1) Postively charged particle called proton.2)Neutrally charged particle called neutron.
2. Energy levels :
The levels which are arranged around the nucleus are known as energy levels.
The energy levels are also called as shells or orbits.
These levels or shells are denoted as K-shell,L-shell,M-shell,N-shell and so on...
The maximum number of electrons in a shell is determined by 2n2
Maximum number of electrons present in first shell or K-shell = 2n2 =2*12 =2
Maximum number of electrons present in second shell or L-shell =2*22 =8
Maximum number of electrons present in third shell or M-shell =2 * 32 =18
Maximum number of electrons present in fourth shell or N-shell =2* 42 =32
Lithium atomic number is 3.It consists of 3 protons and 3 neutons inside the nucleus of an atom.and 3 electons are present around the nucleus which is said to be energy levels.The maximum number of elecctrons present in lithium is Two electrons are present in K-shell and one electron is present in L-shell.