Contributions to The Development of Atomic Model.docx

7/25/2019 Contributions to The Development of Atomic Model.docx

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Democritus Contribution to The Development of

Atomic Model

According to Democritus' atomic theory,

everything is made up of atoms, which are

physically indivisible: atoms are indestructible,

eternal and invisible, small and unable to be

diminished !e posited that atoms occupy space

and di"er in si#e, shape, magnitude, position and

arrangement $n his model, atoms are

homogeneous

%sing this as a basis to the physical world,

Democritus was able to e&plain all changes in the

world as changes in motion of atoms, or changesin the way the atoms were paced together The

theory e&plained physics and combined

mathematics, since its structure was (uantitative

and sub)ect to mathematical laws

The Democritus theory elaborated further on how

nature behaves According to the theory, nature


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is a highly comple& mechanism *hen it comes to

(ualities such as warmth and taste, atoms di"er

only in (uantity and the properties of these

(ualities are only by convention According toDemocritus, atoms and the +oid are the only

things that actually e&ist

$n his theory, he e&plained that by atoms moving

randomly and colliding to form larger bodies was

how the universe began According to

Democritus, the world always e&isted, will forevere&ist and is lled with atoms moving about

randomly

-ohn Daltons Contribution to The Development of

Atomic Model


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!is atomic theory said that elements consisted of

tiny particles called atoms $t states an element is

one of a ind .aa pure/ because all atoms of an

element are identical All the atoms that mae up

the element have the same mass All elementsare di"erent from each other due to di"ering

masses

A compound is a pure .one of a ind/ substance

due to di"erent elements bonded together They

are not easily separated from one another

Compounds have a &ed ratio of atoms 0ach

atom has its own characteristic weight, creating a

weight ratio between elements Also, his theory

said that chemical reactions involve the

rearrangement of combinations of atoms !is

atomic theory stated the general information on

the atom 0verything is made of atoms All atoms

of di"erent substances have di"erent weights


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-- Thomsons Contribution to The Development of

Atomic Model


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$n 1234 the 5ritish physicist -oseph -ohn .- -/

Thomson .12678139/ discovered the electron in

a series of e&periments designed to study thenature of electric discharge in a high;vacuum

cathode;ray tube, an area being investigated by

numerous scientists at the time Thomson

interpreted the de

that he calculated as having a very large value


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for the charge;to;mass ratio ?ater he estimated

the value of the charge itself

$n 139 Thomson suggested a model of the atom

as a sphere of positive matter in which electrons

are positioned by electrostatic forces !is e"orts

to estimate the number of electrons in an atom

from measurements of the scattering of light, @,

beta, and gamma rays initiated the research

tra)ectory along which his student 0rnestutherford moved Thomsons last important

e&perimental program focused on determining

the nature of positively charged particles !ere

his techni(ues led to the development of the

mass spectrograph !is assistant, Brancis Aston,

developed Thomson's instrument further and withthe improved version was able to discover

isotopesatoms of the same element with

di"erent atomic weightsin a large number of

nonradioactive elements


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0rnest utherfords Contribution to TheDevelopment of Atomic Model


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5y 1311 the components of the atom had beendiscovered The atom consisted of subatomic particlescalled protons and electrons !owever, it was not clearhow these protons and electrons were arranged within

the atom -- Thomson suggested theplum puddingmodel $n this model the electrons and protons areuniformly mi&ed throughout the atom:utherford tested Thomson's hypothesis by devising hisgold foil e&periment utherford reasoned that if

Thomson's model was correct then the mass of theatom was spread out throughout the atom Then, if he

shot high velocity alpha particles .helium nuclei/ at anatom then there would be very little to de


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alpha particles could be de


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that energy is transferred only in certain well dened(uantities 0lectrons should move around the nucleusbut only in prescribed orbits *hen )umping from oneorbit to another with lower energy, a light (uantum isemitted 5ohr's theory could e&plain why atoms emittedlight in &ed wavelengths

-ames Chadwics Contribution to The Development ofAtomic Model


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-ames Chadwic discovered the neutron using evidencecollected by $rene -oliot;Curie, who discovered thatwhen beryllium was bombarded with positively chargedalpha particles a beam with a high penetrating powerwas created -ames Chadwic discoverd that this beamwas not de


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Contributions to The Development of Atomic Model.docx

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