3.the Development of Atomic Theory

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The DevelopmentOfAtomic Theory

SMA N 3 SEMARANGSekolah Bertaraf Internasional

2011
http://2.bp.blogspot.com/_HKPlxeYBrS8/TCMD88F5Z8I/AAAAAAAAAGY/8e05ftpHW7s/s1600/smaga.jpghttp://2.bp.blogspot.com/_HKPlxeYBrS8/TCMD88F5Z8I/AAAAAAAAAGY/8e05ftpHW7s/s1600/smaga.jpg


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DEVELOPMENT OF ATOMS MODELS

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Dalton(1803)

Thomson(1897)

Rutherford(1910)

Model atomNiels Bohr

(1913)

MekanikaKuantum(1926)

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Aristotle

400 B.C. - Democritus thought matter couldnot be divided indefinitely.

350 B.C - Aristotle modified an earliertheory that matter was made of four

elements: earth, fire, water, air.

Democritus

Aristotle was wrong. However, his

theory persisted for 2000 years.

fire

air

water

earth

This led to the idea of atoms in a void.

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Development of Atomic

Models

Model Characteristics

Dalton's Atomic Theory stated that:

(a)An element comprises tiny invisible

particles called atoms.(b) Atoms cannot be created nor

destroyed



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Development of Atomic

Models

Model Characteristics

Dalton's Atomic Theory stated that:

(a) An element comprises tiny invisible particles

called atoms.

(b) Atoms cannot be created nor destroyed.

(c) All atoms of a particular element are the

same and have the same mass and physical

features.

(d) Atoms of different elements are differentwith different masses.

(e) Atoms of different elements can combine

chemically in fixed ratios to form compounds.



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Atom is a sphere in which the positive charges spread out evenly in the

atom are neutralized by the negative charges positioned among thepositive charges. Electrons in an atom are like raisins in plum pudding.

Atomic

model Are like

Raisins in

Plum pudding

electron

Positive charges spreadout evenly in the atom

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http://en.wikipedia.org/wiki/Image:Jj-thomson2.jpg


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Electrons

Positively charged goo

A.K.A. the Plum-Pudding Model



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A large fraction of the room in an atom is empty.

Atom has a tiny yet very dense core called thenucleus.

The charge of the nucleus is the same as that of

the alfa particle, which is positive. Atom is composed of a positively charged

nucleus surrounded by negatively chargedelectrons.

Most of the mass in an atom is consentrated inthe nucleus.

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A beam of alfa particles is directed towards the

thin gold plate through alfa slit in the lead plate.Alpha particles that pass the empty space

Go straight through.

Alpha particles that approachthe nucleus are deflected.

Alpha particles that hit thenucleus are bounced back

nucleon

electron

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Sumber sinar Alpha

Lempeng Emas

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Sinar

alfa

Diteruskan

Dibelokkan

Dipantulkan

Atom Logam



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Bohrs Model

Nucleus

Electron

Orbit

Energy Levels17/04/2012 14PPL IAIN WALISONGO_2011


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Bohr Model of Atom

The Bohr model of the atom, like many ideas inthe history of science, was at first prompted by

and later partially disproved by experimentation.

http://en.wikipedia.org/wiki/Category:Chemistry

Increasing energyof orbits

n = 1

n = 2

n = 3

A photon is emittedwith energy E = hf

e- e-

e-

e-

e-

e-

e-

e-

e-

e-

e-

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http://en.wikipedia.org/wiki/Category:Chemistryhttp://en.wikipedia.org/wiki/Category:Chemistry


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An unsatisfactory model

for the hydrogen atom

According to classical physics, lightshould be emitted as the electroncircles the nucleus. A loss of energywould cause the electron to be drawncloser to the nucleus and eventually

spiral into it.

Hill, Petrucci, General Chemistry An Integrated Approach 2nd Edition, page 29417/04/2012 16PPL IAIN WALISONGO_2011


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Modern atomic theory describes theelectronic structure of the atom as the

probability of finding electrons within

certain regions of space (orbitals).

Niels Bohr &Albert Einstein



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The atom is mostly emptyspace

Two regions Nucleus protons and neutrons

Electron cloud region where you might find an

electron



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3.the Development of Atomic Theory

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