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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)

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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

discharge

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

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- 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