John Dalton atomic theory.
John Dalton was a well known scientist he gavw his atomic theory in year 1808.
(photo below)

He gave following points.

• Matter is made of atoms.
• Atom cannot be seen and divided.(proved wrong later)
• Atom of same element are identical that they have same mass and chemical property and atom of different element are different.
• An atom can neither be creted nor destroyed.

Discovery of electron by JJ Thomson.
JJ Thomson discover a subparticle of an atom and proved Daltons point of an atom cannot be divided into further particle wrong .

 

Experiment by which electron was discoverd.

 

JJ Thomson took a discharge tube and connected it with high voltage battery, one end with anode and another with cathode and on reducing pressure from tube he saw some greenish ray coming out from cathode he then placed a plate of negetive and positive charge on upper side and below it repectively.

He saw that these ray is attracted on positive side, and he named it cathode rays. These rays consist of negetive charge called electron.(fig of experiment is below)

 

 

JJ Thomson also gave a model of his own on which electrons are embeded on uniform positive shpere this model was called plum pudding on which raisins are like electron embeded on spherical pudding which was positive sphere.(image below)

 

 

What is an atom?
An atom is the smallest part of an element which takes part in chemical reaction.

an atom

An atom has 3 subatomic particles they are Proton(p+),neutron which makes nucleus and electron(e-)
An atom is electrically neutral because there are the same number of positive and negetive particles which are electron and proton. Neutron is electrically neutral and help in not repulsing proton in nucleus because they have same charge.


Shells or Orbit.
These shells are fixed and on which electron revolve they have fixed amount of energy and different radius. There are 4 shells they are K,L,M,N.
These shells are further divided into subshells which are s,p,d,f,g.
there are some limit to store electron in them and can be calculated by formula 2n*n
there filling is by law of filling of subshell this is represented in below figure.

 

 

and fig of subshellis below.

fig of subshell below.