Unit 2.1 Notes From class
History of the Atom
History of the Atom
Aristotle 4 Elements FIRE AIR WATER EARTH
Democritus
Modern Atomic Theory
John Dalton 1766-1844 English School Teacher Experiments to test atomic theory Studied ratio in which elements combine
Dalton’s Atomic Theory 1. All elements are composed of tiny invisible particles Atoms 2. Atoms of the same element are identical 3. Atoms of different elements can physically mix together/ chemically combine Simple whole number ratios compounds 4. Chemical reactions occur when atoms are separated, joined, or rearranged
J.J. Thompson
Cathode Ray Tube Glowing beam between electrodes Cathode anode (-) (+) Ray attracted to the positive charged plates Bends toward positive
Electron Discovered e- in 1897 Negative particle J.J. Thompson (1856 – 1940) Discovered e- in 1897 Pass an electric current through gas at low pressure Mass 1 /2000 the mass of the H atom Millikan
E. Rutherford https://www.youtube.com/watch?v=ecsgC1wSp5I
Atomic Nucleus University of Manchester, England Alpha particles Ernest Rutherford (1911) University of Manchester, England Alpha particles He that has lost 2 e- 2p + 2n Directed a narrow beam of alpha particles at a thin sheet of gold foil Some pieces went through, while others were bounced backwards
See experiment Atom is mostly empty space Rutherford’s experiment Atom is mostly empty space Positive charge & most of the mass is concentrated in the center Nucleus Central core Protons & neutrons Small compared to entire atom
N. Bohr 1. Electrons travel in fixed paths around the central, positively charged nucleus. ORBITALS / SHELLS 2. Energy Levels – energy is lost or gained when electrons move from one layer to another - Light given off 3. Atom is mostly empty space
J. Chadwick Discovered the neutron Neutron’s mass is nearly equal to the mass of a proton
Neutron Composed of a proton + an electron Overall neutral charge James Chadwick (1932) Latest theory Composed of a proton + an electron Overall neutral charge
Quantum Mechanical Model Electrons are not in rings. Heisenberg Uncertainty Principle – electron position can not be observed but can only be predicted. Electron is a particle that acts like a wave.
Orbitals 4 Types of Orbitals s, p, d, f
Dmitri Mendeleev Russian Scientist Built Periodic Table - atomic masses Using his table, was able to predict missing elements
Henry Moseley Englishman 1914 – Reordered the elements of the Periodic Table Atomic Number = # of protons
Modern Periodic Table
Atom Smallest particle of an element that retains the properties of that element
Proton Positively charged particle Mass is 1840 times the mass of an e- E. Goldstein (1886) Rays traveling in opposite direction of cathode ray # Determines which atom
Cathode Ray Tube Glowing beam between electrodes Cathode anode (-) (+) Ray attracted to the positive charged plates Bends toward positive
Atomic Number # protons in the nucleus Neutral atom Same # p as # e Atoms are different due to the number of e, p, n in each atom Atomic # # protons in the nucleus Neutral atom Same # p as # e Determines position on the periodic table Periodic Table of the Elements
Mass Number # of protons + # of neutrons The mass of the atoms is concentrated in the nucleus Found at the bottom of the element’s square Periodic Table of the Elements
Isotopes Hydrogen Deuterium Tritium
Isotopes Atoms that have the same # protons but different # of neutrons Each isotope will have a different mass # Nature of the element is a combination of the various isotopes Behave chemically the same for the same element Due to p & e
How Do You Write An Isotope mass # A X element Z atomic #
# neutrons = mass # - atomic # Writing Isotopes Carbon-12 Carbon-13 Oxygen-16 Oxygen-17 Oxygen-18 Chromium-50 Chromium-52 Chromium-53 # neutrons = mass # - atomic #
Average Atomic Mass Average of all the masses of the know isotopes of an element
S Orbitals S orbital Groups 1A & 2A 2 electrons Spherical
P Orbitals Groups 13A – 18A 6 electrons total 2 e- in px 2e- in py 2e- in pz
D Orbitals – 10e-
F Orbitals