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Ch.3: The Building Blocks of Matter

Ch.3: The Building Blocks of Matter. 2.1 ATOMIC THEORY OF MATTER. Dalton: all matter is composed of small particles called atoms. Law of conservation of mass – mass is neither created nor destroyed during ordinary chemical reactions or physical changes.

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Ch.3: The Building Blocks of Matter

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  1. Ch.3: The Building Blocks of Matter

  2. 2.1 ATOMIC THEORY OF MATTER • Dalton: all matter is composed of small particles called atoms. • Law of conservation of mass – mass is neither created nor destroyed during ordinary chemical reactions or physical changes. • Law of definite proportions – chemical compound contains the same elements in exactly the same proportions by mass regardless of the size of the sample or source of the compound.

  3. POSTULATES OF DALTON’S ATOMIC THEORY All matter is composed of atoms. Atom: extremely small particle of matter that retains its identity during chemical rxns. Element: type of matter composed of only one kind of atom. Atoms of a given element have a characteristic mass. Compound: type of matter composed of atoms of two or more elements chemically combined in fixed proportions. Ex. Water, 2 H, 1 O Chemical rxn.: rearrangement of the atoms present in the reacting substances to give new chemical combinations present in the substances formed by the rxn. Atoms are not created, destroyed, or broken into smaller particles by any chemical rxn.

  4. ATOMIC SYMBOLS AND MODELS • Atomic symbol: one or two letter notation used to represent an atom corresponding to a particular element. Chlorine: Cl Sodium: Na (latin word natrium)

  5. DEDUCTIONS FROM DALTON’S ATOMIC THEORY - Law of multiple proportions: when two elements form more than one compound, the masses of one element in these compounds for a fixed mass of the other element are in ratios of small whole numbers.

  6. 2.2 THE STRUCTURE OF THE ATOM • Nucleus (positively charged, most mass) • Electron (negatively charged, light)

  7. DISCOVERY OF THE ELECTRON - J.J. Thomson conducted a series of experiments that showed that atoms were not indivisible particles.

  8. How it works. • glass tube with no air, cathode (-), anode (+). • When voltage is turned on the glass tube emits a greenish light. • Greenish light caused by the interaction of the glass with cathode rays (originates for the cathode). • Cathode rays move toward the anode, pass through hole to form beam - Beams bends away from the negatively charged plate and toward the positively charged plate. Concluded that a cathode ray consists of a beam of negatively charged particles (electrons).

  9. Youtube video of cathode ray http://www.youtube.com/watch?v=O9Goyscbazk

  10. From this experiment Thomson could also calculate the ratio of the electron’s mass, me. Large charge to mass ratio. • Ex. Plum pudding model (Thomson) • Millikan exp. • Observed how a charged drop of oil falls in the presence and in the absence of an electric field. • The charge on the electron is found to be 1.602 x 10^-19 coulombs (C) • Found mass of an electron to be 9.109 x 10^-31 kg.

  11. THE NUCLEAR MODEL OF THE ATOM • Rutherford: idea of the nuclear model of the atom • Geiger and Marsden: observed the effect of bombarding thin gold foil with alpha radiation from radioactive substances such as uranium. • Found that most of the alpha particles passed through a metal foil as though nothing were there, but a few (1 in 8000) were scattered at large angles and sometimes almost backward.

  12. Isotopes Atoms of the same element that have different masses. Different numbers of neutrons. Most elements are found naturally with a mixture of isotopes. Ex. Uranium-235 (mass is shown after a hyphen)

  13. Atomic mass unit amu 1 amu is 1/12 the mass of a carbon-12 atom The atomic mass of any other atom is determined by comparing it with the mass of the carbon-12 atom. Average atomic mass Weighted average of the atomic masses of the naturally occurring isotopes of an element. percent found mass Hydrogen-1 99.9885% 1.007825 Hydrogen-2 1.115% 2.014102 0.999885 x 1.007825 amu + .0115 x 2.014102 amu = 1.00794 average atomic mass of element

  14. The Mole A way to group an amount of atoms together so to not deal with huge numbers. Amount of a substance that contains as many particles as there are atoms in exactly 12 g of carbon-12. Just like: dozen, gross, … 1 mole = 6.022 x 1023 atoms Avogadro’s number - 6.022 x 1023 Number of particles in exactly one mole of a pure substance.

  15. Molar Mass The mass of one mole of a pure substance. g/mol The molar mass of an element = atomic mass unit Ex. Carbon 12g  12g/mol Example: 2.00 mol He = _____g He 2.00 mol He x 4.00 g He = 8.00 g He 1 mol He

  16. Calculation How many atoms are in 3moles of H2?

  17. What is the mass in grams of 3.50 mol of the element copper, Cu?

  18. A chemist produced 11.9 g of Al. How many moles of aluminum were produced?

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