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Atomic TheoryThe Movers and Shakers of the Subatomic World.

Dalton In the early 1800s, the English chemist John Dalton did a number of experiments that eventually led to the acceptance of the idea of atoms.

Daltons Atomic Theory All elements are composed of atoms. Atoms are invisible and indestructible particles.

continued... Atoms of the same element are exactly alike.

H

H

continued... Atoms of different elements are different.

O

H

continued... Compounds are formed by the joining of atoms of two or more elements.

H

H

O

Questions... What were the four parts of the Daltons atomic theory? Say it again...

Was he right? Daltons atomic theory of matter became one of the foundations of chemistry.

BUT it needed workother

scientists had to modify the theory.

Thomson In 1897, the work of an English scientist J. J. Thompson provided the first hint that atoms were made up of even smaller particles Atoms are divisibleDalton was wrong!

Thompsons Model He stated that atoms are made up of positively (+) and negatively (-) charged particles

And... He thought the positive (+) and negative (-) particles were s p r e a d o u t in atoms like

ppuldudmisn

(plums in puddin)

Questions... What kind of particles did Thompson find in atoms? What did his idea of an atom look like?

Was Thomson Right? Not reallythere are positively (+) and negatively (-) charged particles inside atoms.

BUT...

Rutherfords Model In 1908, Rutherford discovered the nucleus. He stated that atoms have a small, dense, positively (+)

charged ce

nucleus.

nter called a

Questions... What did Rutherford find inside the atom? What did Rutherfords atom look like?

So... Particles are not spread out like plums in pudding Positive particles (protons)

are in the center (nucleus).

Where are the negative particles (electrons)?

Bohrs Model In 1913, Niels Bohr proposed an improvement to Rutherfords Model: Electrons move in definite orbits around the nucleus, like planets around the sun.

Questions... What did Bohr propose? Where were the particles in Bohrs model of an atom? What did it look like? What was special about the electrons in Bohrs model?

Are we there yet? Bohrs model was used for a long time

BUT...

Modern Atomic Model An atom has a small, positively charged nucleus surrounded

by a in which there are enough electrons (-) to make the atom neutral (0).

large region

E E E E

E

EPPP P PP P P PP P P E

E

E

EE

E

Questions... Do electrons have specific orbits in the modern model? What does the atom look like in the new model?

Make Your Timeline After the sheet is passed out: write your name on it! Fill out the timeline according to date, scientist, notes, and picture (if there is one) for each scientist we went over. Neatness counts!!!!! HAVE FUN