Original Atomic Model • What if I take a sheet of paper and tear it up, and keep tearing it up? • Will we ever get to a “smallest piece possible?” • Democritus – named the atom, from “atomos” meaning indivisible • Matter is made up of indivisible particles-round spheres • Dalton - one type of atom for each element Atomic Models through the years Dalton’s Atomic Theory 1808 • All elements are composed of atoms. Atoms are indivisible and indestructible particles. • Atoms of the same element are exactly alike. • Atoms of different elements have different properties. • Compounds are formed by the joining of atoms in simple, whole-number ratios. • In chemical reactions, atoms are rearranged, but not created or destroyed. JJ Thomson’s Model • Discovered electrons (e-) • Noticed a deflection in a stream of electrons (Cathode Rays) when a negative charge was placed near it. • Atoms have dispersed positive and negative charges • No order to the arrangement of the charges • “Plum-Pudding” model Millikan’s Oil Drop Experiment • The measurement of the electron's charge 1909 and with Thomson's results also a value for the electron mass was obtained. First successful scientific attempt to detect and measure the effect of an individual subatomic particle. For this and his work on the photoelectric effect Robert Millikan won the 1923 Nobel Prize in physics. • Simple • version Rutherford’s Model • Gold Foil Experiment 1911 • Discovered dense positive piece at the center of the atom (nucleus) • Shot positive alpha particles at a sheet of gold foil and noticed “odd” deflections • Electrons moved around the nucleus- planetary model • Atoms are mostly empty space Gold Foil Experiment 1911 + • Rutherford Models Niels Bohr • Student of Rutherford in 1913 • He wanted to know exactly where the electrons are, so explains spectral lines He proposed that the electrons must Move like planets around the sun in circular orbits at different levels BOHR MODELS Certain amounts of energy (quanta) separate one level from another ENERGY LEVELS Bohr’s Model of the Atom Nucleus Electron Orbit Energy Levels Bohr Model •A way of representing electrons in their “orbits” •Every atom has its own Bohr model •Energy Levels: Fill up the inner levels as you go! 1st level 2nd level 3rd level 4th level 2 e8 e8 e2 e- Bohr Model for Lithium James Chadwick • He proved the existence of neutrons.1932 James Chadwick proved that the atomic nucleus contained a neutral particle which had been proposed more than a decade earlier by Ernest Rutherford. • Resulting in the solution of the puzzle for the weight of atoms The Quantum Mechanical Model • Energy is quantized. It comes in chunks. • A quanta is the amount of energy needed to move from one energy level to another. • Since the energy of an atom is never “in between” there must be a quantum leap in energy. • Schrödinger derived an equation that described the energy and position of the electrons in an atom. The Quantum Mechanical Model • The atom is found inside a blurry “electron cloud” • An area where there is a chance of finding an electron is called an orbital • Orbitals do not follow circular (linear) paths, but are instead 3-dimensional shapes Orbitals • The reason for the “blurry” electron cloud is that every electron is found within a region of probability. • The regions, or orbitals, take a variety of sizes and shapes. • These various orbitals stack on top of one another creating the electron cloud.