Chemistry 11Early Models of the Atom

A Short History of Investigating Matter

Around 450 BC, Empedocles suggested that all matter was made of 4 elements:

Earth, Air, Water and Fire

I think this pretty well covers everything!

Empedocles

LOOK OUT SONNY!I could break you right down into atoms! (But

nothing smaller!)

In 500 BC , Democritus proposed that all matter could be broken down into atoms. These atoms could not be broken down farther.

Sorry Democritus!

I am the famous Aristotle and I don’t like your “atom” idea. I disagree and people are going to believe me for 2000 years. So take THAT!

Guys, if we could just

change this lead and copper into GOLD, we’ll be filthy rich! We

can drive around in brand new

SUV’s listening to SIRIUS

satellite radio!Some Alchemists

In the Middle Ages scholars searched for the “Philosopher’s Stone” which would help them change Lead or Copper into GOLD!

Much later, Harry Potter became involved in the same search?????

In 1669, Hennig Brandt distilled some urine. He found a pasty white solid which glowed in the dark!

He had actually discovered a new element “phosphorus”. He didn’t think about it being a new element because he still believed there were only the four.

Hey! This came from pee !!!

NO! I am NOT cutting my hair!!

I also disagree with Aristotle! I think

there are WAY more than four elements!

Sir Robert Boyle

Robert Boyle (1627-1691), an English scientist thought air was a mixture rather than an element. He also thought Brandt’s white paste and gold were elements.

In 1661, Boyle published a book called “The Sceptical Chymist”

HEY! Maybe I can get on the OPRAH

show to help sell my book!

In the late 1700’s the Scientific Revolution was taking place. Many old ideas were being challenged!

“You say you want a revolution, wa-ell you

know-oh oh, we all wanna change the

world….”

Henry Cavendish

Wait a minute! I wrote that song!!!

In 1766, Henry Cavendish mixed a metal with acid making flammable gas which was lighter than air. We now know the gas was _________________

(another element is discovered)

hydrogen

Joseph Priestley (1733 – 1804)

In 1774, Joseph Priestley decomposed mercuric oxide into liquid mercury and a gas. He called the gas “lively air” because it made mice move around faster!

Antoine Lavoisier experimented with Priestley’s gas. He concluded that air must be a mixture of at least 2 gases, one that supports burning and one that does not.Antoine Lavoisier

(1743 – 1794)

Hey! Have you heard about Priestley’s new

gas?

Yeah, sounds cool!

Cavendish took some of his “own” gas (hydrogen) and using Priestley’s method produced some oxygen. He then burned the hydrogen in oxygen and got none other than water! Of course, he wrote a report on this!

I’ve read Cavendish’s report and I think I’ve got

it! When matter is

broken down, the final form is an

element. You can’t break it down any

more!

Antoine Lavoisier

Lavoisier’s wife, Marie also helped in his research but her contribution is seldom mentioned!

I’m going to publish all this

stuff, but I don’t think I’ll mention

Priestley or Cavendish, or even

Marie, for that matter. I’ll also take credit for naming the two gases, hydrogen

and oxygen!

During the French Revolution, Lavoisier was unfortunately executed by the guillotine!That was too bad. He contributed a lot to our knowledge of science and chemistry!

Can someone help me?

In the early 1800’s, John Dalton came up with the ATOMIC THEORY.

 

His main points were:

Dalton’s Atomic Theory1) All matter is made of atoms. Atoms

are indivisible and indestructible.2) All atoms of a given element are

identical in mass and properties 3) Compounds are formed by a

combination of two or more different kinds of atoms.

4) A chemical reaction is a rearrangement of atoms.

Compounds are composed of little “balls” called

atoms, joined together by “bonds” to form molecules.

crookes tube

J.J. Thomson's Experiments

Using Crooke’s tubes and other equipment, J.J. Thomson discovered the electron and measured its e/m (charge to mass) ratio.

Later, “e” was found and the mass of an electron was found to be 9.10938188 × 10-28 grams (much lighter than H)

Thomson’s Plum Pudding Model

Ernest Rutherford

Rutherford’s Scattering Experiment

Applet on Rutherford's Experiment

Rutherford could not explain why the

electron didn’t fall into the nucleus and

destroy the atom.

?

Neils Bohr

I think I can help!

spectra and bohr

Bohr pictured the hydrogen atom as having discrete energy “levels” which the electron could “inhabit”. In it’s ground state, the electron would be in the lowest level (n=1)

When the atom was “excited” the electron could “jump” to a higher level.

When the electron came back down, it released energy in the form of light.

Each “jump” would give off light of a particular wavelength or colour. This gave rise to hydrogen’s spectrum.

According to Bohr, each energy “level” corresponded to a different “orbit” of an electron around the atom. (Like planets around the sun.)

This model is really cool !!

Bohr even calculated what the radii of these orbits would be.

Element 107 on the Periodic Table is called Bohrium (Bh)

In the 1920’s things changed!

Although Bohr’s idea of energy levels was still accepted, his idea of planetary orbits for electrons was rejected!

REJECT ! !

So……

What’s Next???????????????