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Quantum Theory, Part 1. Development of the Atom. History. 400 B.C. LEUCIPPOS and DEMOCRITUS Greek Philosophers Everything that is tangible (able to be touched) is made of atoms, everything else is empty space.

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Quantum theory part 1

Quantum Theory, Part 1


Development of the atom

Development of the Atom


History

History

400 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

Democritus

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”.


History of the atom

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

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.


History1

History

Aristotle (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

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


Quantum theory part 1

“The Alchemist”

Transmutation: changing one substance into another


Quantum theory part 1

Modern Chemistry

• 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.

↑ Pressure = ↓ Volume


Early ideas on elements

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


Quantum theory part 1

Laws

1782 Antoine Lavoisier

  • French

    Law 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


Conservation of mass

High

voltage

High

voltage

After reaction

O2

H2O

0. g H2

40. g O2

300. g (mass of chamber)

+

385 g total

Conservation of Mass

Before reaction

electrodes

glass

chamber

5.0 g H2

O2

H2

80. g O2

45 g H2O

? g H2O

+

300. g (mass of chamber)

385 g total


Law of conservation of matter

10.00 g of lead

11.56 g of

lead sulfide

3.00 g of

sulfur

10.00 g of lead

11.56 g of

lead sulfide

1.44 g of sulfur

(leftovers)

1.56 g of

sulfur

Law of Conservation of Matter

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

+

+

+


Quantum theory part 1

Modern Chemistry

1799 Joseph Louis Proust

  • French

    Law 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)

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


Law of definite proportions

Law of Definite Proportions

Malachite


Law of definite proportions1

10.00 g of lead

11.56 g of

lead sulfide

3.00 g of

sulfur

10.00 g of lead

11.56 g of

lead sulfide

1.44 g of sulfur

(leftovers)

1.56 g of

sulfur

1.56 g of

sulfur

18 g of lead

11.56 g of

lead sulfide

8.00 g of lead

(leftovers)

Law of Definite Proportions

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

+

+

+

+

+


Dalton s atomic theory

Dalton’s Atomic Theory

1803 John Dalton

English School Teacher

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

  • This was called his ATOMIC THEORY.

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

  • 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.

  • 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.

  • 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 Model of the Atom


    Dalton s law of multiple proportions

    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 proportions john dalton 1766 1844

    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


    Quantum theory part 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


    Quantum theory part 1

    Law of Multiple Proportions

    What are the masses of the compounds?

    Law of Conservation of Matter

    Law of Conservation of Matter

    Law of Conservation of Matter

    Law of Conservation of Matter

    1.3333

    2.6667


    Quantum theory part 1

    Law of Multiple Proportions

    According to the Law of Definite Proportions these two substances are different

    According to the Law of Definite Proportions these two substances are different

    1.3333

    2.6667

    What does this tell us?


    Quantum theory part 1

    Law of Multiple Proportions

    1.3333

    2.6667

    What could their formulae be?

    What makes them different?

    #2

    #1

    The second compound has twice as much O as the first


    Proof

    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?!?!?


    Proof1

    What is the significance of these values?

    Proof

    Ratio 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

    What does this mean?


    Quantum theory part 1

    Avogadro’s Hypothesis

    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.

    Gay-Lussac

    Avogadro


    History2

    History

    1833 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

    +

    -

    -

    Goldstein’s Experiment

    Metal

    Cathode

    Anode

    Cathode Ray Tube


    Goldstein s experiment1

    Voltage source

    +

    -

    -

    Goldstein’s Experiment

    Cathode Rays


    Goldstein s experiment2

    Goldstein’s Experiment

    Voltage source

    +

    -

    -

    • Cathode Rays

    • Attracted to positively charged Anode,

    • these rays must be negatively charged.


    Goldstein s experiment3

    Voltage source

    +

    -

    -

    Goldstein’s Experiment


    Goldstein s experiment4

    Voltage source

    +

    -

    -

    Goldstein’s Experiment

    CanalRays

    Attracted to negatively charged plate, hence they must be positively

    charged.


    Quantum theory part 1

    1895Wilhelm 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.


    Quantum theory part 1

    • 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.


    Quantum theory part 1

    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.


    Quantum theory part 1

    • 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.


    Quantum theory part 1

    • 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

    Maltese Cross


    Anyone for a curie

    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.


    Quantum theory part 1

    • 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.”


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