PACE UNIVERSITYChemistry 111Chapter 22.1 -The Atomic Theory A - Summary: Class:John Dalton’s Modern Atomic Theory1) Atoms are the smallest repeating units that compose an element. Atoms that compose an element are identical in size, shape and chemical properties.2) Compounds are the result of combining two or more different atoms with a fixed ratio.3) Chemical reactions are simply the rearrangement of such atomic entities into compounds.Law of Definite Proportions:A substance will have the same ratio and constituents no matter what thesource. Pure substances will always have the same chemical and physical properties.Law of Multiple Proportions:Ratios of the multiple elements combine and can form more than one compound. The ratio is an integer or a small whole number. Example:CO 1:1 CO21:2 or H2O 2:1 H2O2 2:2Law of Conservation of Mass and Energy:Mass and Energy can neither be created nor destroyed: They can simplybe transformed from one substance to another, or transformed from mass into energy.General chemistry equation aA + bB  cC + dD reactants = productsBoth sides of the equation must be equal stoichiometrially!B - Definitions:1 -Law of Definite Proportions - a compound is composed of two or moreelements chemically combined in a definite ratio by weight. 2 - Law of Multiple Proportions: when any two elements (A+B) combine to form more than one compound, the different weights of B that combine with A have a small whole number ratio to each other.3 - Law of Conservation of Mass: mass can neither be created or destroyed. Weight remains constant in an ordinary chemical reaction.4 - John Dalton (1766-1844): an English chemist who first proposed Atomic Theory and later worked on gas laws.2.2 Structure of the Atom: Class:Radioactivity is the spontaneous emission of energy by certain natural ores.Radiation on the other hand is the transmission or emission of energy inspace in the form of particles or waves.Reference to page 39 in book: A lead container is closed on all sides except for a small hole that allows an irradiating beam to travel out of the container. Without an electrical field, the beam passed straight through the gold foil. With an electrical field, the beam was split with one section going towards the anode ( alpha ( + )) while the other is deflected to the cathode (  beta ( - )). The third part of the beam went straight ahead ( gamma (neutral)). The particles in the beams can be ranked by energy: (gamma) has least energy, can be stopped by paper. (beta) has moderate energy; can be stopped by thin metals. (alpha) has the highest energy; needs a very thick metal barrier(i.e.Pb).This theory assumed the beams were all traveling at the same speed. Since opposites attract the protons (+) were drawn to the cathode (-), theelectrons (-) were drawn to the anode (+) and since neutral particles in the beam could not be deflected, the neutral neutrons went straight.J.J.Thompson’s Atomic Theory :He proposed that any atm must be spherical and that the positive protons are evenly distributes throughout the atom. This is the Rahni ‘watermelon’ theory. The protons (seeds) are randomly but evenly scattered throughout the atom.Rutherford’s Atomic Theory:If alpha particles () were sent at Thompson’s theory of the atom, then most of the alpha particles should be deflected by the scattered protons. But it didn’t happen, most of the particles traveled straight through undisturbed. Those that were deflected were near the center of the 2atom. Therefore protons must be clustered near the center in a nucleus.Rutherford calculated that 1/1843 of the space of an atom was occupied by the protons, the rest of the space was occupied by electrons. Based on this Thompson’s Theory was rejected.Reference Table 2.1 on page 40 in text book.MandelevHe found that He has 4x the weight of H but is next in line on the Periodic Table. Therefore the electron is 1/10,000 of the weight of a proton.Chadwick:He bombarded Beryllium with alpha particles and got a mystery ray off ofthe surface. It was like gamma rays but was much heavier. The weight was more like the weight of a proton. He called the new particle a neutron.B - Definitions:1) Atom is the smallest basic unit of an element that can enter into a chemical reaction. It is also the smallest unit that cannot be broken down into another chemical substance.2) Electron is the negatively charged, subatomic particle with a very low mass.3) Radioactivity is the spontaneous breakdown of an atom by the emission of particles or radiation.4) Radiation: the emission or transmission of particles through space as waves or particles.5)  Rays or particles: are helium ions with a positive charge of +2.6)  Rays or particles are electrons or negatively charged particles.7)  Rays or particles are high energy radiation.8) Proton is a subatomic particle with a single positive charge. The mass of a proton is 1840 times greater than an electron.9) Nucleus: is the center of an atom.10) Neutron is a subatomic particle with no net charge. It mass is slightly more than a proton.11) J.J. Thompson (1856 - 1940): British physicist received the Nobel Prize for discovering the electron.12) Wilhelm Roentgen ( 1845 - 1923): German physicist who won the Nobel Prize for the discovery of x-rays (1901).13) Robert Andrew Millikan (1868 - 1953): American physicist who determined the charge of an electron. (Nobel Prize 1923).14) Antoine Becquerel (1852 - 1908): French physicist won the Nobel Prize for discovering radioactivity in uranium (1903)315) Marie Curie (1867 - 1934): won the Nobel Prize twice for her work on radioactive elements (1911) and on radioactivity (1903).16) Ernest Rutherford (1871 - 1937): New Zealand physicist that received the Nobel Prize for investigations into the atomic structure of the nucleus (1908).17) Johannes Geiger (1882 - 1945): German physicist who worked on radiation and atomic nucleus theory. Best as the inventor of the Geiger counter.18) James Chadwick (1891 - 1972): British physicist who won the Nobel Prize for the discovery of neutrons (1935).C - Problems:9-How many helium atoms between first and last in a cm:cm = 1 x 10 -10 pm1 x 10-10 pm/cm  1 x 102 pm / He atom = 1 x 108 He atoms / cm28- Calculate charge (coulombs) and mass (grams) for 1 mole of electrons:a- Mass / electron = 9.09 x 10-2g x 6.022 x 10 23 electrons/ mole =5.47 x 1026 g/moleb--1.76 x 10 8