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Atomic Theory Chapter 4
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History sdfgfdsdfgsdfg
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Democritus 400BC Greek philosopher
Thought all matter was made up of atoms (atomos), which are the basic, indivisible particles of matter
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Aristotle Believed all matter was continuous-did not believe in atoms
His opinion was accepted for nearly years
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Late 1700’s Scientists agreed that
Most natural materials are mixtures of pure substances. Pure substances are elements or compounds. Law of constant composition-a compound always has the same composition.
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John Dalton English schoolteacher who tied all three laws together in his atomic theory Dalton turned Democritus’s idea into a scientific theory that could be tested by experimentation.
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Dalton’s Atomic Theory
Elements are made of tiny particles called atoms. All atoms of a given element are identical. The atoms of an element are different from those of any other element. Atoms of one element combine with others to form compounds. Atoms are indivisible in chemical processes. A chemical reaction changes the way the atoms are grouped together.
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Joseph John Thomson Cathode-ray experiment: showed that the atoms of any element can be made to emit tiny negative particles Determined the charge ratio of electrons
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William Thomson Plum pudding model-a bunch of positive stuff with the electrons scattered throughout.
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Rutherford, Geiger, Marsden-nucleus
Gold foil experiment, which led to the discovery of the nucleus. Like bullets through a tissue
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Florescent Screen Lead block Uranium Gold Foil
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What he expected
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Because, he thought the mass was evenly distributed in the atom.
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What he got
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+
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Atomic Structure
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Protons The number of protons in an atom determines the element’s identity Nuclear forces hold the nuclear particles together The atomic number equals the number of protons
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Electrons Are very small.
If the nucleus is a grape, the electrons would be about one mile away. Have a negative charge The arrangements of electrons determines the element’s chemical properties.
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Neutrons Mass number= protons+neutrons
Neutrons=mass number-atomic number Isotope-atoms that have the same number of protons and electrons but different numbers of neutrons (disproves point 2 of Dalton’s theory) Nuclide-any isotope of any element
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Table 2.1 The Mass and Charge of the Electron, Proton, and Neutron
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Practice- Give the protons, neutrons, and electrons for each
Mercury Sodium Carbon 13C 6
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Answers Mercury 80p, 80e, 121n Sodium 11p, 11e, 12n Carbon 6p, 6e, 6n
13C p, 6e, 7n 6
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Ions An ion is formed when we remove or add an electron to a neutral atom. Cation-a positive ion Anion-a negative ion
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Ion Example Regular sodium has 11 electrons, 11 protons, and 12 neutrons. If we take away 1 electron, it would have 10 electrons (-), and 11 protons (+) so the charge would be +1. (Neutrons would stay the same).
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Periodic Table
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Organization Groups/families-vertical columns Periods-horizontal rows
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Metals Conductors Lose electrons (cations +) Malleable and ductile
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Nonmetals Brittle Gain electrons (anions -) Covalent bonds
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Semi-metals or Metalloids
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Alkali Metals
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Alkaline Earth Metals
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Halogens
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Transition metals
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Rare Earth Metals (Inner transition metals)
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Noble Gases
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Periodic Table Label the following on your periodic table
Group Charge 1 and and Group Charge none
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+1 -4 -3 -2 -1 +2 +3 +1 +2
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Trends Notice that metals tend to give up electrons while nonmetals tend to gain electrons.
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Ionic Compounds Contains a metal and a nonmetal (causes ions that is why it is called ionic) The net charge of an ionic compound has to be zero.
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Ionic Compound Examples
Sodium chloride Na +1 Cl NaCl Magnesium chloride Mg +2 Cl -1 MgCl2
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