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The Evolution of the Atom

Published byAlyson Hunt Modified over 8 years ago

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Presentation on theme: "The Evolution of the Atom"— Presentation transcript:

1 The Evolution of the Atom
From the Beginning to the End (so far…)

2 John Dalton ( 1766-1844) 1808 First to use the word atom
Featureless sphere Analogy = billiard ball

3 Dalton’s Atom

4 J.J. Thomson ( ) 1897 Positive sphere with negative charges embedded Analogy = Raisin bun or plum pudding

5 JJ Thomson Link to demo Used the technology of the cathode ray tube
It is a glass tube that puts gas under pressure, with electrodes attached at either end Gas conducts electricity when under pressure Link to demo

6 J.J. Thomson’s Atom

7 H. Nagoaka ( ) Saturnian model of the atom first proposed in 1904 Positive sphere with a ring of negative charges Negative charges = ELECTRONS Analogy = SATURN!

8 Rutherford 1909 – Gold Foil Experiment
Small positive nucleus surrounded by electrons ANALOGY = beehive

9 Gold Foil Experiment 1909 Used to “see” inside an atom
Alpha Particles = HIGH energy Used a beam of Alpha Particles from polonium Alpha particles were SHOT through a piece of GOLD foil

10

11 THE RESULTS Link to demo
MOST of the alpha particles went through the gold foil HOWEVER, a small number of the alpha particles BOUNCED back!!

12 Three Conclusions A NUCLEUS – a tiny core that is very small in volume BUT very DENSE and Positively charge ELECTRON CLOUD – a large volume containing electrons surrounding the nucleus NEUTRONS- the nucleus was heavier than expected, so there must be another particle that has a mass BUT NO CHARGE

13 Rutherford’s Atom

14 Bohr (1885-1962) 1921 PROBLEM WITH Rutherford's experiment
Why, if positive and negative attract, don’t the electrons negatively charged electrons CRASH into the positively charged nucleus ?

15 Reminder Opposite ATTRACT i.e. Positive attracts Negative Likes REPEL
i.e. Positive repels Negative

16 ANSWER! The electrons are traveling in orbits
The speed at which prevents them from crashing into the nucleus

17 Bohr’s Atom Positively charged particles (PROTONS) found in the nucleus Neutral charged particles (NEUTRONS) found in the nucleus Negatively charged particles (ELECTRONS) in orbits surrounding the nucleus

18

19 HOW SMALL IS AN ATOM? if the electrons was the diameter of a hair
then the entire atom's diameter would be greater than the length of thirty football fields! % of an atom's volume is just empty space!

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