Download Unit 4: History of the Atom

UNIT 4:
HISTORY OF THE ATOM
HISTORY OF THE ATOM
MODELS OF THE ATOM
DALTON’S ATOMIC THEORY
MODERN ATOMIC THEORY
LEARNING TARGETS FOR TODAY:
• I can state which scientist discovered each particle and cite evidence
for how each particle was discovered (DOK 1 and DOK 3).
• I can explain the historical models of the atom (DOK 2)
• I can state the charge of each atomic particle (DOK 1)
• I can locate each atomic particle in the atom (DOK 1)
ANCIENT GREEKS
• There was no science
• No controlled experiments
• Little Technology
• Ideas came from life experiences
DEMOCRITUS (460-370 B.C.)
• First to suggest that matter was NOT indefinitely divisible.
• Matter was made up of atomos – that which cannot be split
• Atomos moved through empty space
• Atomos could not be created nor destroyed, or divided.
ARISTOTLE (384-322 B.C.)
• Did not believe in Democritus’s atoms
• Did not believe in empty space
• Matter was indefinitely divisible
• Believed all matter was: Earth, Fire, Water and Air
• Since he was the leading mind, at the time, no one
challenged his ideas of 2000 years.
THE ALCHEMIST: 400-1400 AD
• First to do “science”
• First to use experimentation to prove ideas
• First to use symbols to identify elements
• Attempted to turn lead into gold
• Many of their discoveries lead to the modern
science of Chemistry
JOHN DALTON 1766 – 1844 AD
• English chemist and meterologist
• Revived and revised Democritus’s ideas using scientific
research
• Matter is made up of atoms
• Matter is indivisible and indestructible
• Developed the first atomic theory
DALTON’S ATOMIC THEORY (1808)
• Atoms of given elements (the same element) are identical in size,
mass, and chemical properties.
• Atoms of one element differ from those another element.
• Atoms combine in simple whole number ratios to form compounds
• In reactions, atoms are separated, combined, or rearranged.
*Had to be revised as new data was collected.
MODERN ATOMIC THEORY
*Started with Dalton’s Atomic Theory, and was only changed slightly, through new discoveries.
• Matter is indestructible and made up of atoms
• Atoms are the smallest particle of an element that retains the properties of a
specific element
• Atoms of the same element can vary in mass
• Atoms are divisible, into smaller subatomic particles – protons, neutrons,
electrons
• Atoms combine in simple whole number ratios to form compounds
• In reactions, atoms are separated, combined, or rearranged. (Law of
Conservation of Matter)
DALTON’S ATOMIC THEORY
VS.
MODERN ATOMIC THEORY
Dalton’s Atomic Theory
Modern Atomic Theory
• Matter is indivisible and indestructible
• Matter is indestructible and made up of atoms
• Matter is made up of atoms
• Atoms are the smallest particle of an element that retains
the properties of a specific element
• Atoms of given elements (the same element) are
identical in size, mass, and chemical properties.
• Atoms of one element differ from those another
element.
• Atoms combine in simple whole number ratios to
form compounds
• In reactions, atoms are separated, combined, or
rearranged.
• Atoms of the same element can vary in mass
• Atoms are divisible, into smaller subatomic particles –
protons, neutrons, electrons
• Atoms combine in simple whole number ratios to form
compounds
• In reactions, atoms are separated, combined, or
rearranged. (Law of Conservation of Matter)
HOW DOES THE ATOM LOOK?
• Scientist wanted to know what the atom looked like.
• Scientist knew a couple things, and those became the basis for their
models:
• Matter was neutral
• Matter has mass
Atoms
J.J. THOMSON (1897)
• Plum Pudding Model:
• Believed the atom was like plum pudding (said the pudding was the
positive matter and the plums were negative particles)
• The atom was mostly positively charged, but had negatively charged
particles embedded in it. (Like chocolate chips in a chocolate chip cookie)
• Believed it was spherical shaped
• Cathode Ray Experiment
• Discovered the Electron
J.J. Thomson
ERNEST RUTHERFORD (1911)
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Gold Foil Experiment
Disproved his professor/teacher J.J. Thomson
Suggested that atoms have a nucleus
Suggested another subatomic particle
Hinted to a 3rd subatomic particle
Suggested electrons were “orbiting” the nucleus
Proton – Electron Attraction
GOLD FOIL EXPERIMENT
• Shot a beam of radiation at a thin sheet of gold
• Hypothesis was based on the Plum Pudding Model
• Expected particles to go straight through the piece of gold foil, unless they hit an electron
• Some particles were reflected back to the firing machine, and then deflected in different
directions.
• He expected that some would be deflected as they hit an electron here and there, but he did
not expect ANY to be reflected.
GOLD FOIL EXPERIMENT
• Shot a beam of radiation at a thin sheet of gold
• Hypothesis was based on the Plum Pudding Model
• Expected particles to go straight through the piece of gold foil, unless they hit an electron
• Some particles were reflected back to the firing machine, and then deflected in different
directions.
• He expected that some would be deflected as they hit an electron here and there, but he did not
expect ANY to be reflected.
*Lead to Rutherford’s model and idea about the Atom – giving shape to the Modern Atomic Theory.
ERNEST RUTHERFORD (1911)
• Atom is made up of mostly empty space
• Electrons moved around in the empty space
• Positive part of the atom was at it’s center
• Nucleus – a small dense positively charged space at the center of an atom
• Electrons were held within the atom due to their attraction to the nucleus
• Electrons are attracted to the positive charge of the nucleus, keeping them
attached to that atom, and not drifting in space.
• The diameter of the atom was calculated to be 10,000 times the diameter of the
nucleus
• If an atom were 2 football fields, the nucleus would be a nickel
ERNEST RUTHERFORD (1920)
• The Nucleus
• Made up of protons and another subatomic particle
• Makes up 99.97% of the atom’s mass
• Protons are a positively charged subatomic particle
• Another subatomic particle with a neutral charge
• Electrons
• Negatively charged
• Surround the nucleus, not in the nucleus
• Found on the electron cloud
• Negligible to the mass of an atom
• Attracted to the positive charge of the protons in the nucleus
• Protons and electrons are attracted to each other
• Atoms are mostly empty space
Rutherford
JAMES CHADWICK (1932)
• English Physicist
• Won the Nobel Prize in Physics in 1932
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For his discovery of the neutron
• Student of Rutherford
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Cofound the neutron
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Proved the existence of the 3rd subatomic particle – Rutherford’s idea
• The Neutron
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Contributes, almost equally as the proton does, to the atom’s mass
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Electrically neutral – how it got it’s name
GELL-MANN AND ZWEIG (1964)
• Proposed that protons and neutrons were made up of smaller
particles
• Little is known about these particles
• They are called “quarks” – overall term
Quarks
Quarks 2
MODERN ATOMIC THEORY
• Follows Rutherford’s ideas and model of the atom from
1920
• Protons and Neutrons are divisible into smaller particles
called quarks
• Quarks are still in their infancy in the world of science
• they are still a new discovery and still being figured out
HOMEWORK
• Complete page 1 front and back: What is
Matter
• Complete page 2 front only: Who Am I?