Chemistry 6AH - Chapter 1 Notes

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  • 8/6/2019 Chemistry 6AH - Chapter 1 Notes


    Chapter 1 Notes : The Atom in Modern Chemistry

    1.1 The Nature of Modern Chemistry- Alchemists were the first chemists, wrongly attempting to take extrinsic characteristics of metals to

    make gold

    - The Scientific Methodo Hypothesis: temporarily accepted new idea after passing several rigorous tests becomes ao Scientific Law: accurately explains results of experiments and must also be predictive

    - Conversation of Mass + Conservation of Energy- Macroscopic = visible ( 1m 1mm)- Nanoscopic = not visible to the naked eye ( < 1nm)

    1.2 Macroscopic Methods of Classifying Matter- Analysis: taking things apart- Synthesis: putting things together- Matter

    o Heterogenous: can be separated in 2+ phaseso Homogenous: uniform but not necessarily pure

    mixture: can be separated chemically

    substance: cannot be physically separatedy compound: 2+ elementsy element: cannot be decomposed ordinarily (excludes radioactive decay)

    1.3 Indirect Evidence for the Existence of Atoms: Laws of Chemical Combination- Laws of Chemical Combination: reactions involving definite mass ratio

    o provide evidence of atoms and molecules- Laws of Conservation of Mass: in every chemical operation an equal quantity of matter exists

    before and after the operation

    - Law of Definite Proportions: in a given chemical compound, the proportions by mass of theelements that compose it are fixed

    o outliers of this law, most commonly solids, are called berthoillides or nonstoichiometriccompounds (occurs because transition metals have various oxidation states)

    - Daltons Atomic Theory (Atomic Theory of Matter)1. Matter consists of indivisible atoms2. All atoms of an element are identical *proved wrong3. Different elements have different atoms (with their own masses)

  • 8/6/2019 Chemistry 6AH - Chapter 1 Notes


    4. Atoms are indestructible and retain identity in reactions5. A compound forms from atoms of elements in whole number ratio

    - Law of Multiple Proportions: when two elements form a series of compounds, the masses of oneelement that combine with a fixed mass of the other element are in the ratio of small intergers to

    each other

    - Law of Combining Volumes: the volumes of two reacting gases (at the same T and P) are in a ratio.Moreover, the raio of the V of each product of gas to the volume of either reacting gas is the ratio.

    o Avogadro improved this postulate- Avogadros Hypothesis

    o Equal volumes of different gases at the same T and P contain equal numbers of particleso Took into account diatomic molecules

    was discredited because the belief of affinity but correctly identified relative atomicmass (for H2O, 1g H for 8g O)

    1.4 The Physical Structure of Atoms- Electrons

    o Founded by JJ Thomsons cathode rays which were described to be negative charge carrierparticles

    o Thomsons apparatus measured charge to mass ratio (e/ me)o Charge to mass ratio = 1.7588 X 1011 C kg-1o Millikan discovered charge, e = 1.6021746 X 10-19 C

    - The Nucleuso Gas discharge tubes were used by Wein in discovering massive positively charged particles

    in gas (called plasmas) that when an electric field was applied, emitted light called glow


    o Ernest Rutherford shot alpha particles at gold foil, some, which bounced back discovered the nuclei nuclei consists of proton + neutrons

    - Mass Spectrometry and Relatives Masseso Mass spectrometry: most accurate way of determining relative atomic masseso Isoptope: Same elements with different relative masses (neutrons)o Relative molecular mass: sum of the relative atomic masses of the elements that constitute

    it (water = 18.01 g)

    o Relative atomic masses have no units calculated by multiplying isoptopic mass X abundance

  • 8/6/2019 Chemistry 6AH - Chapter 1 Notes


    - Protons, Neutrons, and Isotopeso Protons

    Proton positive charge opposite of electron mass = 1.67262 X 10-27 kg, 1836 times greater than an electron

    o Neutrons uncharged, mass close to that of a proton

    o Nuclide aka nuclear species1.5 Imaging Atoms, Molecules, and Chemical Reactions

    - Scanning Tunneling Microscopy Imaging of Atomso uses low energy electrons, unlike the electron microscope which damaged the sample

    - Imagine and Controlling Reactions at the Single Molecule Level Using Scanning TunnelingMicroscope

    o see pages 24-25