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History of the atom And The Atom’s Properties Aristotle and Democritus ◦ Aristotle did not believe in atoms. Empty space? ◦ Democritus came up with the word “atom” from atomos meaning indivisible. Thought they were the smallest unit of matter and could not be broken down. History of the atom Joseph Proust ◦ Law of definite proportions Whenever two elements combine to make a compound, they do so in a definite proportion by mass Start of stoichiometry History of the atom John Dalton ◦ Dalton’s Atomic Theory Matter consists of small particles called atoms. All atoms of one particular element are identical and their properties are identical. Atoms are indestructible. In chemical reaction, the atoms rearrange or combine, but are not destroyed. Atoms of different elements have different properties. When atoms of different elements combine to form compounds, they combine in a ratio of whole numbers. ◦ Supports the Law of Conservation of Mass History of the Atom Joseph Gay-Lussac and A. Avogadro ◦ Studied ratios of combined gases. ◦ Did not fully understand correct chemical formulas and atomic masses until Amedeo Avogadro came along. ◦ Avogadro’s number 6.02 x 1023 History of the atom JJ. Thompson “Plum pudding model” ◦ Negatively charged particles that could be removed from the atom. ◦ SUBATOMIC Particles called ELECTRONS. History of the Atom Robert A. Millikan “Millikan Oil-Drop Experiment” ◦ Determined the mass and charge of an electron ◦ 1.6 x 10 -19C ◦ 9.10 x 10-28 g 1/2000 the mass of a proton History of the atom Ernest Rutherford “Gold Foil Experiment” ◦ Discovered a NUCLEUS And that it was POSITIVELY CHARGED ◦ PROTONS Hans Geiger was his student. History of the Atom Niels Bohr ◦ “BOHR MODEL OF THE ATOM” ◦ Orbits and energy levels of electrons ◦ Jump between energy levels- Quantum mechanics History of the Atom Werner Heisenberg Understood that there are certain parameters of a particle that can’t be measured simultaneously. How can we take measurements of or collect data about an electron? Heisenberg said it is physically impossible to measure simultaneously the exact position and exact linear momentum of a particle. If Δx is small then Δpx is large and vice versa. We cannot measure position, time, velocity of a particle with precision. Heisenberg Uncertainty Principle Basic Equations C f E hf h 6.63 x10 34 J s c 3.00 x10 m / s 8 Equations Equations ◦ Energy of a photon: hc E hf ◦ Momentum of a photon: E hc h p c c Heisenberg’s Uncertainty Principle Equations: xp x h xp x h 4 h 4 remember : p mv Et Mass of an electron = 9.11 x 10-31 kg Heisenberg Uncertainty Principle Albert Einstein PHOTOELECTRIC EFFECT Won the Nobel Prize for this ◦ Collision between a particle of light(photon) and an electron on the surface of a metal. ◦ Entry doors ◦ Photodiode: Pixel ◦ Video camera tubes ◦ Moon dust ◦ Solar cells Photoelectric Effect Parts: Nucleus: Neutrons, Protons Outer shell: electrons Properties of the Atom Properties http://www.falstad.com/qmatom/ Atomic mass: number of protons and neutrons Atomic number: number of protons Isotope: same element different mass. Ion: Charged atom. Gained or lost electrons. Anion-negative Cation-positive Properties of the Atom Behavior ◦ ◦ ◦ ◦ ◦ Neutral atom when protons = electrons Ion- different number of electrons Only electrons move to or from the atom. Responsible for behavior of atom/element. Octet rule Properties of the Atom Electrons ◦ Quantum behavior ◦ EM spectrum Properties of the Atom Electrons in discrete energy levels. n level Broken into smaller levels: ◦ s, p, d, f Quantum Mechanics Quantum Mechanics
