General Chemistry I: Chapter 0
General Chemistry I: Chapter 0 CHE 1101
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12050 - BIOL 3350 - 001
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This 3 page Bundle was uploaded by Hannah Czajkowski on Friday January 29, 2016. The Bundle belongs to CHE 1101 at Appalachian State University taught by Jennifer Cecile in Spring 2016. Since its upload, it has received 27 views. For similar materials see General Chemistry1 in Chemistry at Appalachian State University.
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Date Created: 01/29/16
A Brief History of Chemistry: Matter and Movement Chapter 0 Atomic theory- John Dalton, 1813 o Descried atoms and how they interact with one another Careful laboratory observation o Can lead to understanding the atomic world Energy change and probability o Lead to predictions about chemical interactions Geometric shapes of molecules are important, affect properties, reactivity, and function (DNA, RNA, proteins) Atomic Theory o Most significant theoretical model of nature based on the atom o Atom Smallest particle that has all properties of give element Makes up all chemical substances and contains tiny submicroscopic particles Is building block for everything in the macroscopic world o Law of definite proportions In a given compound the elements are always combined in the same proportion by mass Always fine 1 g H to 8 g O in water o Law of conservation of mass No detectable gain or loss of mass occurs in chemical reactions, mass is conserved A closed vessel with 16 g O and 2 g H will weigh 18 g after water is formed form them o Daltons atomic theory developed to explain theses phenomena (1813) Matter consists of tiny particles called atoms Atoms are indestructible In chemical reactions atoms rearrange but do not brake apart In any sample of a pure element all atoms are identical in mass and other properties Atoms of different elements differ in mass and other properties In a given compound constituent atoms are always present in same fixed numerical ratio o Proof of Atoms 1980's, Scanning Tunneling Microscope (STM) Scan surface of materials for topographical information Shows spherical regions of matter to five proof of atoms Subatomic particles o Protons and electrons have a charge o Protons and neutrons have essentially the same mass o The mass of an electron is so small we ignore it o Electrical charge Electron: -1 Proton: +1 Neutron: 0 -24 o 1 amu =1.66054x10 g Electron Discovery o Thomson 1897-stream of negatively charged particles in cathode rays o Discovered negatively charged particles moving from the cathode (- electrode) to the anode (+ electrode) o After deflecting cathode rays through magnetic and electric fields, Thomson determined charge to mass ratio (e/m) of these particles e/m=-1.76x10 coulombs/gram o Millikan Oil Drop Experiment (e- mass) Measured electron charge e- = -1.60x10 -19 Used with Thomson's e/m to find electron mass -28 e- mass = 9.10x10 g Coulomb is the SI electrical charge unit Atom Compositions o Plum pudding model (Thomson) Positive sphere of matter of matter with negative electron imbedded in it Electrons have a small mass; therefore, they are a small fraction of atom's size Radioactivity o Spontaneous emission of radiation by an atom o Radiation types (Rutherford's contribution) o Alpha and Beta particles bent by an electrical field toward charged plates, gamma rays are unaffected Atomic Nucleus Composition o Rutherford's scattering experiment o Repulsion from gold atoms, so atoms must contain heavy positively charged nuclei contrary too Thomson's model o Modern model of atom nucleus Proton Discovery o 1918 in Ernest Rutherford's lab o Discovered in detected using a mass spectrometer o Smallest positively charged particles Nuclear Atom "Modern" o Nucleus Has almost all of mass in atom Has all of positive charge Is located in very small volume at center of atom Neutron Discovery o Discovered in 1932 by James Chadwick, but postulated by Rutherford and others Estimated number of positive charges on nucleus based on experimental data Nuclear mass based on this number of protons always far short of actual mass (by 1/2 the actual mass) o Another type of particle must be present with same mass as proton o Electrically neutral Size of atoms o Atoms are ex-10mely sma-10 1x10 to 5x10 m in diameter Angstroms (A) 1x10 -10m (non-SI unit) o Atomic nucleus: 10 A - a small fraction of an atom's diameter o 13 14 3 Density of a nucleus: 10 to 10 g/cm Atomic Structure o Atoms have an equal number of protons and electrons--no net charge (# electrons = # protons) in a neutral atom o Nucleus filed with protons and neutrons o Electrons fill the rest of the atom o Electrons are attracted to protons in the nucleus. A balance of attractive and repulsive forces controls atomic size Atomic Notation o Atomic Number (Z) Number of protons that atom has in nucleus Unique to each type of element Element is substance whose atoms all contain identical number of protons o Isotopes Atoms of same element with different masses Same number of protons Different number of neutrons Mass number (A) = protons + neutrons Atomic number (Z) = protons or electrons (doesn’t change) Atoms of the same element with different masses. Most elements are mixtures of two or more stable isotopes Isotopes have virtually identical chemical properties Isotopes have different numbers of neutrons as distinguished by mass number A. Sometimes called C-12, C-11 to give mass number # neutorns= mass number- atomic number
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