Atom
Atom is a Greek word which means indivisible they believed that matter can be broken down into very small indivisible particles .
1. In other words we can say atoms are fundamental building blocks of matters.
2. Matter composed of three subatomic particles the proton ,the neutron and therefore the electrons.
1. In other words we can say atoms are fundamental building blocks of matters.
2. Matter composed of three subatomic particles the proton ,the neutron and therefore the electrons.
Atomic theories.
The atomic theory given
by maharishi kanad . an ancient indian scientist and philosopher propounded a theory of atom.He explain the creation and existence of the universe.
1 . He explain his atomic theory of matter in his book vaisheshika Sutra also called kanad Sutra .
2 . According to kanad everything can be subdivided .
3 . That subdivision leads to creation of parmanu (atom) which are the smallest entities .
4 . Parmanu (atom) is not visible to the naked eye .
5 . Atom are indestructible, indivisible and it cannot be further divided.
6 . Earth ,fire ,water ,air those are made up of parmanu , but sky ,time ,space are not the combination of parmanu (atom) .
7 . Parmanu (atom) have two State
a. State of motion
b. Absolute rest
8. He explain nityam mandalam (in Sanskrit गोलाकार ) that means a atom has a spherical shape .
According to dalton's atomic theory :-
• the discovery of atomic theory is attributed to jhon Dalton English chemist, physicist, and meteorologist.
1. All matter made up of extremely small particles called atom.
2. It is indivisible.
3. It is indestructible.
4. Two or more diffrent kinds of atom form a compound.
5. A chemical reaction is a rearrangement of atoms .
6 . He explain the formation of different kinds of molecules by the combination of different atoms .
7. Understand the origin and nature of electromagnetic radiation absorbed or emitted by atoms .
Discovery of electron
Electron was discover by j.j Thomson in 1897 time .
J.J Thomson began experimenting with cathode ray tubes .
A cathode ray tube is made of glass containing two thin pieces of metal ,called electrodes, are vaccum- sealed glass tubes that have had most of the air removed At one end of the tube, a high voltage is placed between two electrodes causing a stream of particles to flow from the cathode ( the negative charged electrode) to the anode ( the positive charged electrode) because the particle beam . The flow of current from cathode to anode the ray can be detected by painting a material known as phosphorus onto the far end of the tube beyond the anode . The phosphorus spark ,or emit light when impacted by the cathode ray .
Thomson also placed two magnets on both side of the tube, and observed that this magnetic field also deflected the cathode ray with this information and Thomson's
mass of an electron .
Mass/charge ×charge =mass
Charge on the electron ÷
Thomson model of atom (plum pudding theory ):-
The plum pudding model given by j.j Thomson . It is a historical scientific model of the atom.
According to this model, the atom is a spehre who surrounded by a volume of positive charge like blue berries stuck into a muffins.or a plum pudding and negatively charged electrons are embedded in it to balance the positive charge . The electrons are like plum or blue berries in a pudding or muffins.
However this model was discarded when Rutherford performed the famous alpha particles scattering experiment. This model was simillar to our solar system . With electrons revolving around a positively charged,dense nucleus.
Rutherford's nuclear model of atom
Rutherford and his student (hans Geiger and Ernest Marsden )
Conducted his famous Alpha- particles scattering experiment in which a stream of high energy Alpha particles was directed at a thin foil of gold . The gold foil had a circular fluorescent zinc sulphide screen around it whenever Alpha - particles is the a particles struck the screen, a tiny flash of light was produced at that point.
Rutherford tested Thomson's hypoth-esis by devising his gold foil .
• the gold foil was selected so as to obtain an extremely thin layer. The thickness of the gold foil was about 1000 atoms .
• doubly - charged He (helium) ions are known as alpha particles, rapidly moving Alpha- particles possess a great deal of energy as, they have a mass of about 4amu .
--->> the hypothesis was that Alpha-particles would be deflected by the sub- atomic particles in the gold atoms .
Rutherford drew the following conc-lusions :-
1. Most of the space in the atom is empty as most of the Alpha- particles passed through the foil undeflected.
2. A few positively charged Alpha-particles were deflected.
The deflection due to the enormous repulsive force .
3. The positive charge has to be concentrated in a very small volume that repelled and deflected the positively charged Alpha-particles.
4. Rutherford showed the volume occupied bt the nucleus negligibly small as compared to the total volume of the atom .
Atomic number and mass number :-
Atomic number :- atomic no. Is defined as the total no. Of protons or electrons in an nucleus of each atom of the element.
It is represented by the latter Z
Example : - carbon atomic no. Is 6 and it has 6 no. Of protons.
Mass number :- an elements mass no. Is the total number of the protons and the number of neutrons .(the small role of mass from electrons ) .it is represented by the latter A
Example :- carbon atom no.
Of protons =6 , no. Of neutrons = 6
Mass = 12
Isotopes and isobars
Isotopes :- those elements that have the same atomic number but different mass number are referred to as isotopes.
Example :- considering of hydrogen (H) atom 99.985% of hydrogen atoms contain only one proton .
This isotope called protium ( H1) .
Rest of percentage of hydrogen atom contains two isotopes
1 proton and 1 neutron called deuterium .(D2)
And other one possessing 1 proton and 2 neutron called tritium .(T3)
Isobars :- the atoms having the same mass number . But a different atomic number.
Example :- atomic no. Of Argon (Ar) is 18 and mass number is 40 , the atomic number is Potassium (k) is 19 and the mass number is simillarly 40
And also calcium is 20 and the mass number is 40 .
So Ar, K Ca are the same mass number But different atomic number so they isobars .
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