The Evolution of the The Evolution of the AtomAtom

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Unit Essential Unit Essential QuestionQuestion

What ideas lead to the What ideas lead to the modern concept of the modern concept of the

atom?atom?

The Atom GuysThe Atom Guys

Democritus was a pre-Socratic Greek philosopher. Democritus was a student of Leucippus, and co-originator of the belief that all matter is made up of various imperishable indivisible (or perhaps undivided) elements which he called "atoma", from which we get the English word atom. It is virtually impossible to tell which of these ideas were unique to Democritus, and which are attributable to Leucippus.According to legend, Democritus was thought to be mad because he laughed at everything, and so he was sent to Hippocrates to be cured. Hippocrates pointed out that he was not mad, but, instead, had a happy disposition. That is why Democritus is sometimes called the “laughing philosopher.”

450 to 370 BC

“Nothing exists except atoms and empty space;

everything else is opinion”

““What if you cut some cheese? What if you cut some cheese? What I mean is…What I mean is…How many times can you How many times can you

cut it until it is no longer a piece of cut it until it is no longer a piece of cheese?” cheese?”

And concluded….And concluded…. ““There is a limit of how far something can be divided”There is a limit of how far something can be divided” The smallest divisionThe smallest division

(the part where it can no longer be cut)(the part where it can no longer be cut) would be the “Atoma” (Atom)would be the “Atoma” (Atom) ““All matter is made up of atoms”All matter is made up of atoms” ““Different combination of these atoms result in Different combination of these atoms result in

different types of matterdifferent types of matter.” .” (Fire -Water – Earth – Air)(Fire -Water – Earth – Air)

EQ: What ideas lead to the modern concept of the atom?

For 2300 years Democritus’ concept of the Atomos was believed then…

EQ: What ideas lead to the modern concept of the atom?

John Dalton, British chemist and physicist is known as one of the fathers of modern physical science. One if his major accomplishments is the development of Dalton's Atomic Theory (Don’t copy, look it up) 1. Elements are made of tiny particles called atoms 2. All atoms of a given element are identical 3. The atoms of a given element are different from those of any other element 4. Atoms can combine form compounds. 5. Atoms cannot be created, divided or destroyed. Amazingly, all but two of the statements in Dalton's Atomic Theory are still believed to be true by scientists today. The 3rd statement is not precisely true, as the different isotopes of an element have varying numbers of neutrons in their nuclei, though the number of protons remains consistent. In addition, the 5th statement is inconsistent with the discovery of the p+, no & e- and the existence of nuclear fusion and fission.

1766 to 1844

“This paper will no doubt be found interesting by

those who take an interest in it”

Daltonism – color blindness

John Daltons’ 1803 Atomic TheoryJohn Daltons’ 1803 Atomic Theorya. Elements are made of tiny particles called

atoms

carbon-carbon- oxygen-oxygen-

b.b. Atoms of the same element have the same Atoms of the same element have the same massmass

and atoms of different elements have and atoms of different elements have differentdifferent

massesmasses

c. c. Compounds contain atoms of more than oneCompounds contain atoms of more than one elementelement carbon dioxide-carbon dioxide-

d. d. Atoms of different elements always combine Atoms of different elements always combine inin

the same waythe same way CO CO2 2 -- COCO22

e. e. Atoms are the smallest particle of matter and cannot be created, divided or destroyed.

C O

C C CO

CO O

CO O CO O

Amidst glowing glass tubes and the hum of electricity, the British physicist J.J. Thomson was venturing into the interior of the atom. His experiments prompted him to make a bold proposal: these mysterious rays are streams of particles much smaller than atoms, they are in fact minuscule pieces of atoms. He called these particles "corpuscles," and suggested that they might make up all of the matter in atoms. It was startling to imagine a particle residing inside the atom--most people thought that the atom was indivisible, the most fundamental unit of matter. Thompson had discovered the electron. Thompson declared that the electrons was suspended in a mass of + charged matter.

1856 to1940

Thompson’s Plum Pudding model

Research in applied science leads to reforms, research inpure science leads to revolutions, and revolutions are exceedingly profitable things if you are on the winning side.

First to look inside the atom.First to look inside the atom. Atoms have an equal number of Positively and Atoms have an equal number of Positively and

Negatively charged particles. (making it Negatively charged particles. (making it neutral)neutral)

DISCOVERED THE ELECTRON!DISCOVERED THE ELECTRON! Negative particles are suspended in a Positive Negative particles are suspended in a Positive pudding-like masspudding-like mass

Plum Pudding modelPlum Pudding model

Electrons

Positive Pudding

EQ: What ideas lead to the modern concept of the atom?

Real plum pudding

Return to presentation

This is the Cathode Ray experiment that Thomson did.-The green beam is an electric charge (electrons) sent through a gas filled tube.1.The positive side of a magnet is introduced to the tube and the beam is attracted to it.2.The magnet is flipped to the negative side. Observe what happens to the beam.

1871 - 1937

Ernest Rutherford described the atom as having a central positive nucleus surrounded by negative orbiting electrons. This model suggested that most of the mass of the atom was contained in the small nucleus, and that the rest of the atom was mostly empty space. Rutherford came to this conclusion following the results of his famous gold foil experiment. This experiment involved the firing of particles through minutely thin metal foils (Au) and detecting them using screens coated with zinc sulfide. Rutherford found that although the vast majority of particles passed straight through the foil approximately 1 in 8000 were deflected leading him to his theory that most of the atom was made up of 'empty space'.

“In science there is Physics, and the rest is just stamp

collecting.” Rutherford earned 3 university degrees but could not get hired as a school teacher

Ernest RutherfordErnest Rutherford Rutherford didn’t believe there was any Rutherford didn’t believe there was any

“Pudding”. The positive charges were “Pudding”. The positive charges were particles.particles.

Rutherford asked one of his students Rutherford asked one of his students Robert Marsden, to test Thompson’s Robert Marsden, to test Thompson’s Plum Pudding model by firing model by firing alpha alpha particlesparticles through gold foil to see if how through gold foil to see if how much deflection there was.much deflection there was.

A small deflection was expectedA small deflection was expectedMarsden

What was happening?

e-

Hard, dense nucleus

Missed me!

Ouch!

Stop that!

Foul Ball!

Thomson’s Positive Pudding

ConclusionConclusion About 1 in every 20,000 particles were About 1 in every 20,000 particles were

deflected. (more than Rutherford had deflected. (more than Rutherford had expected)expected)

Not all of the positive charge is spread Not all of the positive charge is spread throughout the atom. (there’s no pudding)throughout the atom. (there’s no pudding)

There was something in the middle that was There was something in the middle that was hard and dense (Nucleus)hard and dense (Nucleus)

Also reveals that the nucleus is positively Also reveals that the nucleus is positively charged, and claims discovery of the charged, and claims discovery of the proton.proton.

Those particles not deflected passed Those particles not deflected passed through the LARGE open space between the through the LARGE open space between the electron and nucleus.electron and nucleus.

“There are some things so serious that you have to

laugh at them.”

1885 to 1962

Niels Bohr, born in Denmark, made numerous contributions to our understanding of atomic structure and quantum mechanics. He won the 1922 Nobel Prize for physics, chiefly for his work on the structure of atoms. In 1913 Bohr published a theory about the structure of the atom based on an earlier theory of Rutherford's. Bohr expanded upon this theory by proposing that electrons travel only in certain successively larger orbits. He suggested that the outer orbits could hold more electrons than the inner ones, and that these outer orbits determine the atom's chemical properties. Bohr also described the way atoms emit radiation by suggesting that when an electron jumps from an outer orbit to an inner one, that it emits light. Later other physicists expanded his theory into quantum mechanics. This theory explains the structure and actions of complex atoms.

Fun fact: http://tenonline.org/art/usa/0009.html

Agreed with Rutherford, but focused Agreed with Rutherford, but focused on Electronson Electrons

- outer orbits hold more e- and have - outer orbits hold more e- and have more energymore energy

- e- gain/lose energy and change - e- gain/lose energy and change energy levelsenergy levels Developed the Developed the

Planetary ModelPlanetary Model

EQ: What ideas lead to the modern concept of the atom?

“Thus, the task is, not so much to see what no one has yet seen; but to think what nobody has yet thought, about that which everybody sees.”

1887 to 1961

The Austrian theoretical physicist Erwin Schrodinger laid the foundation of the wave-mechanics approach to quantum theory and set forth his now-famous wave equation. Schrodinger shared the Nobel Prize for physics with Paul Dirac for his contributions to atomic theory. He continued his studies of the application and statistical interpretation of wave mechanics, the mathematical character of the new statistics, and the relationship of these statistics to statistical thermodynamics. He also worked on problems of general relativity and cosmology and on a unified field theory. Late in his life Schrodinger studied the foundations of physics and their implications for philosophy

It’s possible that he disliked cats.

Extended the ideas of Bohr and the Extended the ideas of Bohr and the electronelectron

Electrons are particles AND wavesElectrons are particles AND waves Electrons are never in one place Electrons are never in one place

(probability)(probability) If we try to observe them, they may no If we try to observe them, they may no

longer be there. longer be there. It doesn’t matter where the e- is – It It doesn’t matter where the e- is – It

doesdoes matter how much energy it has. matter how much energy it has.Schrödinger's cat

EQ: What ideas lead to the modern

concept of the atom?

Is it dead?

Is it alive?

Is it both?

1891 to 1974

For four years, James Chadwick was a prisoner of war in Germany. When World War I ended, he returned to his native England to rejoin the mentor of his undergraduate days, Ernest Rutherford. Rutherford had discovered the nucleus, but they and other researchers were finding that the proton did not seem to be the only particle in the nucleus. Chadwick was able to determine that the neutron did exist and that its mass was about equal to the proton's. He published his findings with characteristic modesty in a first paper entitled "Possible Existence of Neutron." In 1935 he received the Nobel Prize for his discovery. His findings showed that the neutron had to be its own unique particle -- the third piece of the atom to be found. Physicists soon found that the neutron made an ideal "bullet" for bombarding other nuclei, splitting the atom and releasing the huge amounts of energy predicted by Einstein's equation E = mc2 in 1905.

Worked with Rutherford on Nucleus ideasWorked with Rutherford on Nucleus ideas They found that the They found that the Atomic numberAtomic number (#P)was (#P)was

much smaller than much smaller than Atomic massAtomic mass (???) (???) Repeated the radiation experiments of Fred Repeated the radiation experiments of Fred

and Joliot (Madame) Curie, and found another and Joliot (Madame) Curie, and found another particle with the same mass as the proton, but particle with the same mass as the proton, but with with no charge!no charge!

FOUND THE NEUTRON!FOUND THE NEUTRON! Received the Nobel Prize for finding the Received the Nobel Prize for finding the

Neutron.Neutron. His discovery allowed E=MCHis discovery allowed E=MC22 to create the to create the

Atom Bomb.Atom Bomb.EQ: What ideas lead to the modern concept of the atom?

1929 -

Gell-Mann entered Yale University at the age of 15.

If someone says that he can think or talk about

quantum physics without becoming dizzy, that

shows only that he has not understood anything whatever about it.

In 1963, Gell-Mann and American physicist George Zweig independently postulated the existence of the quark, an even more fundamental elementary particle, inside the proton and neutron, with a fractional electric charge; quarks are confined in protons, neutrons, and other particles by forces associated with the exchange of gluons. Gell-Mann and others later constructed the quantum field theory, or the field of Quantum Physics. Gell-Mann was awarded the 1969 Nobel Prize for Physics.

Quarks are fundamental matter particles that Quarks are fundamental matter particles that make up pmake up p++ and n and n00. There are six different . There are six different types of quarks. Each quark type is called a types of quarks. Each quark type is called a flavor.flavor.

Ups and Downs make upUps and Downs make up P+ and NP+ and N00

Flavor Mass(GeV/c2)

Electric Charge(e)

u up 0.004 +2/3

d down 0.008 -1/3

c charm 1.5 +2/3

s strange 0.15 -1/3

t top 176 +2/3

b bottom 4.7 -1/3

What three quarks are in a P+?

What three quarks are in a N0?

Up + Up + Down

+2/3 +2/3 -1/3 = +1Up + Down + Down

+2/3 - 1/3 - 1/3 = 0 EQ: What ideas lead to the modern concept

of the atom?

The EndThe End