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Different Models of Atom
1. Dalton's Atomic Model:
Dalton’s atomic model is one of the fundamentals of physics and chemistry. This theory of atomic composition was hypothesized and partially confirmed by the English chemist and Physicist John Dalton. Dalton came with his Atomic theory as a result of his research into gases. He discovered that certain gases only could be combined in certain proportions even if two different compounds shared the same common element or group of elements. Through deductive reasoning and experimentation, he made an interesting discovery. His findings led him to hypothesize that elements combine at the atomic level in fixed ratios.
This ratio would naturally differ in compounds due to the unique atomic weights of the elements being combined. This was a revolutionary idea but further experimentation by himself and others confirmed his theory. The findings became the basis of Dalton’s Atomic Laws or Model. These laws focus on five basic theorems.
2. Thomson’s model or Plum Pudding model or Raisin Pudding model or water melon model:
Thomson stated that atom is uniform sphere of positive charge with negatively charged electron embedded in it in such a way that atom becomes electrically neutral.
Rutherford’s Nuclear Model of Atom:
α-Particle scattering experiment:-
A beam of α-Particle was projected towards this gold foil. The foil was surrounded by circular fluorescent ZnS screen which produces flash when α -Particle collides with it.
Observations of experiment:
On the basis of scattering experiment, Rutherford proposed an atomic model or nuclear atomic model or nuclear model of atoms.
Radius of nucleus
Radius of nucleus is of the order of 10-15m and radius of atom is order of 10-10m
A= Mass number=no. of protons + no. of neutrons.
Failures of Rutherford’s Model:
Waves and its characteristics:
It is a periodical disturbance causing transfer of energy without transfer of matter.
Amplitude: Maximum displacement from mean position it remains constant with distance except stationary or standing waves.
Wavelength: It is the distance between two adjacent crest or troughs.
Frequency (): The no of waves passing through a point in 1 second, unit-sec-1 or Hz
Wave number: No. of waves present in unit distance.
Velocity: linear distance travelled by wave in one second.
NATURE OF LIGHT
An accelerated electrically charged particle produces and transmits electrical and magnetic field. These are transmitted in the form of waves known as electromagnetic waves or electromagnetic radiations. He stated that light also possess electrical and magnetic field and therefore it is also known as electromagnetic radiations or e.m.w.
But Maxwell theory couldn’t explain the results of photoelectric effect and black body radiations.
Photon Energies for EM Spectrum
A blackbody is an object that emits a well-defined spectrum of radiation solely based on its temperature. We see from figure at right that the hotter the blackbody, the more intense it is, and the shorter the peak wavelength. The picture does not say anything about what the object is made of, or how heavy it is, etc. It doesn't matter! The only property that determines the spectrum of a blackbody is its temperature. Brick, iron or a dense gas will emit the same spectrum as long as they are at the same temperature. That spectrum will have a peak that lies at a particular wavelength.
[Particle nature of light];
He stated that a radiates energy in the form of discontinuous energy packets or bundles. Each bundle of energy is known as quantum and quantum of light is known as photons.
Energy of each quantum is directly proportional to frequency of radiation.
Total energy absorbed or emitted by a body will be whole no. integral multiple of energy of quantum
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