Quantum Theory, Part 1

Development of the Atom

History400 B.C. LEUCIPPOS and DEMOCRITUS

– Greek Philosophers– Everything that is tangible (able to be touched) is made

of atoms, everything else is empty space.– Matter can be broken down into atoms, which are the

smallest particles of matter. “ATOMOS”– Solid and Indestructable– Different materials are made up of different types and

mixtures of atoms.– Different sizes and shapes of atoms lead to different

properties. – NO EXPERIMENTAL EVIDENCE

“To understand the very large,

we must understand the very small.”

DEMOCRITUS (400 BC) – First Atomic Hypothesis

Atomos: Greek for “uncuttable”. Chop up a piece of matter until you reach the atomos.

Properties of atoms:• indestructible.• changeable, however, into different forms.• an infinite number of kinds so there are an infinite number of elements.• hard substances have rough, prickly atoms that stick together.• liquids have round, smooth atoms that slide over one another.• smell is caused by atoms interacting with the nose – rough atoms hurt.• sleep is caused by atoms escaping the brain.• death – too many escaped or didn’t return.• the heart is the center of anger.• the brain is the center of thought.• the liver is the seat of desire.

“Nothing exists but atoms and space, all else is opinion”.

Democritus

History of the Atom• Looked at beach

– Made of sand• Cut sand

– Smaller sand• Smallest possible

piece?– Yes!!!!– “Atomos” -

indivisible

Some Early Ideas on Matter

Empedocles (Greek, born in Sicily, 490 B.C.)– Suggested there were only four basic seeds

– earth, air, fire, and water. – The elementary substances (atoms to us) combined in

various ways to make everything.

Aristotle (Greek, born 384 B.C.)– Added the idea of “qualities”

– heat, cold, dryness, moisture – as basic elements which combined as shown in the diagram (previous page).

– Hot + dry made fire; hot + wet made air, and so on.

HistoryAristotle (prized pupil of Plato)

– Greek Philosopher– Matter is made of a continuous substance

called “hyle”– Matter can be infinitesimally broken down.

There is no such thing as a smallest particle.– 4 elements make up all substances.

» Fire - hot» Air - light» Earth - cool, heavy» Water - wet» Blend these in different proportions to get all

substances – NO EXPERIMENTAL EVIDENCE

Who Was Right?• Greek society was slave

based.• Beneath the “Famous” to work

with hands.– Thus, they did not

experiment.• Greeks settled disagreements

by argument.• Aristotle was more famous.• He won.• His ideas carried through until

the 17th century.

Followed by the onset of alchemy and The Sceptical Chymist

“The Alchemist”

Transmutation: changing one substance into another

• Beginnings of modern chemistry were seen in the 16th and 17th centuries, where great advances were made in metallurgy, the extraction of metals from ores.

• In the 17th century, Boyle described the relationship between the pressure and volume of air and defined an element as a substance that cannot be broken down into two or more simpler substances by chemical means.

Modern Chemistry

↑ Pressure = ↓ Volume

Early Ideas on Elements

Robert Boyle stated...

– Air therefore could not be an element because it could be broken down into many pure substances.

Robert Boyle

Laws1782 Antoine Lavoisier

– FrenchLaw of Conservation of Mass (Matter)

– Matter can not be created nor destroyed.

– Translation: In ordinary chemical reactions, the total mass of the reactants is equal to the total mass of the products.

– First Experimental evidence:

Mass of Sn + Mass of O = Mass of Sn and O

45 g H2O? g H2O

Conservation of MassHigh

voltage

Before reaction

electrodes

glasschamber

5.0 g H2

80. g O2

300. g (mass of chamber)+

385 g total

H2O2

Highvoltage

After reaction

0. g H2

40. g O2

300. g (mass of chamber)+

385 g total

O2

H2O

Law of Conservation of Matter

+

10.00 g of lead 1.56 g ofsulfur

11.56 g of lead sulfide

+ +

10.00 g of lead 3.00 g ofsulfur

11.56 g of lead sulfide

1.44 g of sulfur(leftovers)

Pb – soft, grayish metalS – pale yellow solid

PbS – lustrous, black solid

1799 Joseph Louis Proust– FrenchLaw of Definite Proportions (Constant Composition)

– Each compound has a specific ratio of elements» Translation: Compounds have an unchanging chemical

formula.

– It is a ratio (proportion) by mass

– This holds true regardless of the origin, how it was obtained, or how large a sample.

» Water is always 8 grams of oxygen for every one gram of hydrogen (8:1)

» NaCl is table salt. It is always 1.54 g Cl (chlorine) for every 1.0 g Na (sodium).

Modern Chemistry

Law of Definite Proportions

Malachite

Law of Definite Proportions

+

10.00 g of lead 1.56 g ofsulfur

11.56 g of lead sulfide

+ +

10.00 g of lead 3.00 g ofsulfur

11.56 g of lead sulfide

1.44 g of sulfur(leftovers)

+ +

18 g of lead 1.56 g ofsulfur

11.56 g of lead sulfide

8.00 g of lead(leftovers)

Pb – soft, grayish metalS – pale yellow solidPbS – lustrous, black

solid

Dalton’s Atomic Theory1803 John Dalton English School Teacher

– Created the first logical hypothesis about the existence of atoms.

– This was called his ATOMIC THEORY.

1) All matter is composed of small particles called atoms, that are indivisible and indestructible.

2) Atoms of each element are identical. In particular, they have the same mass and properties. Atoms of different elements are different. They have different masses and properties.

3) Chemical changes involve the combination, separation, or rearrangement of atoms. Atoms are not created, destroyed, divided into parts, or converted into other kinds of atoms.

4) Compounds are formed when atoms combine. Each compound has a specific number and kinds of atom. They are combined in definite whole-number ratios.

Dalton’s Model of the Atom

Dalton’s Law of Multiple Proportions

• Dalton could not use his theory to determine the elemental compositions of chemical compounds because he had no reliable scale of atomic masses.

• Dalton’s data led to a general statement known as the law of multiple proportions.

• Law states that when two elements form a series of compounds, the ratios of the masses of the second element that are present per gram of the first element can almost always be expressed as the ratios of integers.

Law of Multiple ProportionsJohn Dalton (1766 – 1844)

If two elements form more than one compound, the ratio of the second element that combines with 1 gram of the first element in each is a simple whole number.

Two substances are decomposed and determined to be made of both oxygen and hydrogen. When the masses of the elements are analyzed, it is found out the

O:H O:H

16:2

= 8:1

32:2

= 16:1

What?

• Water is 8 grams of oxygen per gram of hydrogen.

• Hydrogen peroxide is 16 grams of oxygen per gram of hydrogen.

• 16 g to 8 g is a 2:1 ratio

• True, because you have to add a whole atom, you can’t add a piece of an atom.

If the formula for water is H2O,

then the formula for hydrogen peroxide is

H2O2

Law of Multiple Proportions

1.3333 2.6667Law of Conservation

of Matter

Law of Conservation

of Matter

Law of Conservation

of Matter

Law of Conservation

of Matter

What are the masses of the compounds?

Law of Multiple Proportions

What does this tell us?

1.3333 2.6667

According to the Law of Definite

Proportions these two substances

are different

According to the Law of Definite

Proportions these two substances

are different

Law of Multiple Proportions

1.3333 2.6667

#1

#2What makes them different?

What could their formulae be?

The second compound has twice as much O as the first

Proof• Mercury has two oxides. One is 96.2 % mercury by

mass, the other is 92.6 % mercury by mass.

For every 100. grams of substance

A: B:

96.2 g Hg 92.6 g Hg

3.8 g O 7.4 g O

• Show that these compounds follow the Laws of Conservation of Matter, Definite Proportions, and Multiple Proportions.

• How much oxygen must there be? WHY?!?!?

ProofRatio of Hg:O

= 25.315789 g Hg / g O = 12.513513 g Hg / g O

25.315789 / 12.513513= 2.02 = 2.0

Substance A has 2x as much Hg to O as Substance B

• Speculate on the formula of the two oxides.

If Substance B = HgO then Substance A = Hg2O

96.2 g Hg

3.8 g O

92.6 g Hg

7.4 g O

What is the significance

of these values?

What does this

mean?

Gay-Lussac– French

• Attempted to establish the formulas of chemical compounds by measuring, under constant temperature and pressure conditions, the volumes of gases that reacted to make a given chemical compound, together with the volumes of the products if they were gases.

– Compounds always react in whole number ratios by volume.

Avogadro– Italian

• Gay-Lussac’s results were explained by Avogadro’s hypothesis, which proposed that equal volumes of different gases contain equal numbers of gas particles when measured at the same temperature and pressure.

Avogadro’s Hypothesis

Gay-Lussac

Avogadro

History1833 Michael Faraday

– British– Proved that electricity is made of fundamental

particles.

1886 Eugene Goldstein– English

Used Crooke’s tube (cathode ray tube) to study canal rays.

These rays were oppositely charged cathode rays. Credited with the discovery of the proton.

Goldstein’s Experiment

Voltage source

+--

Cathode Anode

Cathode Ray Tube

Metal

Goldstein’s Experiment

Voltage source

+--

Cathode Rays

Goldstein’s Experiment

Voltage source

+--

Cathode Rays• Attracted to positively charged Anode, these rays must be negatively charged.

Goldstein’s Experiment

Voltage source

+--

Goldstein’s Experiment

Canal Rays

Voltage source

+--

Attracted to negatively charged plate, hence they must be positively

charged.

1895 Wilhelm Conrad Röntgen – German

Discovered X-rays by accident Covered the Lenard tube with lightproof paper and projected the

cathode rays onto various objects. Piece of fluorescent material glowed under exposure to the

cathode rays. Moving the fluorescent material further and further away from

the Lenard tube -- glowed up to 2 meters away. Röntgen knew that the cathode rays could not penetrate the

lightproof covering over the Lenard tube Hypothesized that the glowing of the fluorescent material

must be the result of some new kind of radiation. He began experimenting with putting different materials and

objects between the Lenard tube and the fluorescent material and observing how the radiation passed through them.

His wife put her hand in the path of the cathode ray. The shadows from his wife’s hand over a photographic

plate clearly showed the bones inside her hand and her wedding ring, while her flesh became transparent.

Röntgen named his discovery X-rays because of their unknown properties.

1896 Henri Becquerel– French

Discovered radioactivity by accident Fascinated by the strange ghostly images and the mysterious

emanations produced from Röntgen's X-rays. Both he and his father had studied the phenomenon of

phosphorescence . When exposed to sunlight, material gives off light.

Laboratory filled with lumps of stone and wood that shone in the dark.

He thought immediately of putting some phosphorescent rock on photographic paper to see if it would darken it in the same way as one of Röntgen's X-ray sources.

He exposed the material to sunlight and placed it on photographic plates wrapped in black paper.

When developed, the plates revealed an image of the uranium crystals.

Becquerel concluded "that the phosphorescent substance in question emits radiation which penetrates paper opaque to light."

Initially he believed that the sun's energy was being absorbed by the uranium which then emitted X rays.

Further investigation was delayed because the skies over Paris were overcast and the uranium-covered plates Becquerel intended to expose to the sun were returned to a drawer.

As a check, he then developed the photographic plate and found that the fogging had again occurred, even though the uranium salt could not have phosphoresced since it had been in darkness for some days. This meant that the uranium emitted radiation without an external source of energy such as the sun.

To see whether the effect depended on the uranium salts having previously been exposed to sunlight at all, Becquerel next prepared the salts in darkness.

He also performed the experiment in darkness, but found the same result – the fogging of the photographic plate did not depend on phosphorescence.

After further work, his newly discovered rays could pass through metal plates and still fog the photographic plate, though less intensely.

Becquerel had discovered radioactivity, the spontaneous emission of radiation by a material.

"There is an emission of rays without apparent cause. The sun has been excluded."

The phenomenon was found to be common to all the uranium salts studied and was concluded to be a property of the uranium atom.

Rays emitted by uranium caused gases to ionize They differed from X-rays in that they could be deflected by electric

or magnetic fields. Must be charged particles.

Maltese Cross

Anyone for a Curie Somehow, the uranium was able to give off rays

of energy spontaneously. He suspected some unknown element in uranium

ore to be the cause. Becquerel hired Marie Curie as an assistant to

isolate this unknown element which spontaneously gave off high amounts of energy.

With her husband Pierre, Madame Curie took Pitchblende, which contained the radioactive element Uranium by the ton and carefully isolated the radioactive components over several years.

What they found was that there were more than one radioactive element in it because they found an element that was far more radioactive than the element uranium.

The Curies isolated a new chemical element which spontaneously emitted energy. They named it Polonium after their native country.

Four years later, the Curies isolated another substance that released lots of energy. This new element was called radium. The Curies coined the terms “radiation” and “radioactivity.”