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History of Chemistry. Discoveries and Atoms. Early Greeks. Democritus – all matter is made of small, indivisible particles called “atomos” Aristotle – matter is continuous and NOT made of smaller particles. Robert Boyle (1600’s). 1 st true “chemist”
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History of Chemistry Discoveries and Atoms
Early Greeks • Democritus – all matter is made of small, indivisible particles called “atomos” • Aristotle – matter is continuous and NOT made of smaller particles
Robert Boyle (1600’s) • 1st true “chemist” • Discovered a relationship between pressure and volume (Boyle’s Law)
Antoine Lavoisier • Matter cannot be created or destroyed Law of Conservation of Mass
Joseph Proust • Found that a given compound always contains exactly the same proportion of elements by mass Law of Definite Proportions
John Dalton (1800’s) • The ratios of the masses of elements in a compound can always be reduced to small whole numbers Law of Multiple Proportions
Dalton’s Atomic Theory • 1) all matter is composed of tiny particles called atoms • 2) the atoms of an element are always identical while the atoms of different elements are different • 3) compounds form when atoms combine; atoms combine in small whole number ratios • 4) reactions involve reorganization of atoms; the atoms themselves do not change
Dalton • Proposed the “Billiard-ball model” of the atom
Joseph Gay-Lussac (1809) • Measured the volumes of gases that reacted with one another to develop the Law of Combining Volumes of Gases
Amadeo Avogadro • at the same temperature and pressure, equal volumes of gases contain the same number of particles Avogadro’s hypothesis
J.J. Thomson • Produced a “cathode ray” which was deflected by a negative electric field • Thus the ray must be made of negative particles (electrons)
J.J. Thomson • Since atoms are neutral, they must also have a positive area • Plum pudding model
J.J. Thomson • Protons were found to be 1836 X the mass of an electron • Charge of proton is +1
Robert Millikan • Oil drop experiment to determine the magnitude of the electron’s charge which is now known as -1
James Chadwick • Discovered high energy particles with no charge and the same mass as the proton – the neutron
Henri Becquerel • Accidentally discovered radioactivity • Alpha particles (+2 charge) • (Also beta particles, gamma rays)
Ernest Rutherford (1911) • Tests Thomson’s Plum Pudding Model by shooting alpha particles through a sheet of gold foil
Ernest Rutherford • Nuclear Model of the Atom
Robert Bunsen • Found that when heated, different elements produced different colors in a flame
Niels Bohr (1912) • Electrons “orbit” the nucleus somewhat like planets orbit the sun • Planetary Model
Arnold Sommerfeld • Expanded the Bohr model Electrons travel in orbitals, but the orbitals are not the same shape -- this leads to the electron cloud model of the atom
Wolfgang Pauli (1924) • Predicted that electrons spin while orbiting the nucleus Pauli’s Exclusion Principle says no two electrons do the exact same thing at the same time
de Broglie and Schrödinger • Propose that electrons move like wave thus the Wave-Mechanical Model
WernerHeisenberg • No experiment can measure the position and momentum of a quantum particle simultaneously Heisenberg’s Uncertainty Principle
Modern View of the Atom • Tiny nucleus surrounded by electron “cloud” • Nucleus accounts for all of the mass • Arrangement of electrons causes different chemical properties
Electron Cloud Model • Note: Just as no map can equal a territory, no concept of an atom can possibly equal its nature. These models of the atom simply served as a way of thinking about them, though they contained limitations (all models do).
