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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) • • • • • • • 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 • For his discovery of the neutron • Student of Rutherford • Cofound the neutron • Proved the existence of the 3rd subatomic particle – Rutherford’s idea • The Neutron • Contributes, almost equally as the proton does, to the atom’s mass • 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?