Chemistry 11 Early 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

I could break you right down into atoms! (But nothing smaller!) 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 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.

HEY! Maybe I can get on the OPRAH show to help sell my book! In 1661, Boyle published a book called “The Sceptical Chymist” HEY! Maybe I can get on the OPRAH show to help sell my book!

Wait a minute! I wrote that song!!! 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….” Wait a minute! I wrote that song!!! Henry Cavendish

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

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!

Joseph Priestley (1733 – 1804)

Antoine Lavoisier experimented with Priestley’s gas 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! Hey! Have you heard about Priestley’s new gas?

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, by George! 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! Can someone help me? That was too bad. He contributed a lot to our knowledge of science and chemistry!

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

His main points were: Dalton’s Atomic Theory 1) 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. ?

I think I can help! Neils Bohr

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

This model is really cool !! 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??? ????????????