Theories and facts eventually tend to suggest certain
fundamental ways in which physical universe is organized.
Law of gravity
Law of conservation of energy
Chemistry
The study of matter and its changes.
Scale (size): between physics and biochemistry.
This course ambitious enough to include biochemistry.
States of Matter
solid
liquid
gas
Pure Substances
Separate particles all have same numbers and kinds
of atoms and bonds between atoms. Can be elements or compounds.
diamond, sugar, water, oxygen
Mixtures
milk, peanut butter, cement
Elements
Composed of only one kind of atom.
Atoms can be alone (argon) or bonded together in pairs
(oxygen), threes (ozone), fours (phosphorus), eights (sulfur),
forties (C40), sixties (C60),
or zillions (carbon as diamond).
Compounds
Composed of more than one kind of atom. Particles
can be molecules, macromolecules, or macroscopic objects (rubber
ball).
Death of "indestructable" attribute of atom
came about with discovery of protons, neutrons, and electrons.
Invention of vacuum pump in 1870's led physicists to
experiment with vacuum tubes. Tom Edison involved- attempts to
improve light bulb.
Cathode Rays: 1879 (Crookes)
Protons: 1886 (Goldstein/Wein)
Electrons: 1897 (Thompson; capacitors & magnets
on Crooks Tubes)
Neutrons: 1932 (Chadwick; neutrons from reactor knock
protons from wax)
Milliken (1909) determined amt of charge (q) on an
electron. q/m was determined by Thompson in 1897, so now m could
be calculated. q/m for protons figured out in 1886.
Assuming q for protons and electrons equal with opposite
sign (overall electrical neutrality) then proton weighs about
2000 times as much as electron.
Assuming sizes of protons and electrons proportional
to their masses, Rutherford developed "Plum Pudding"
model of atom- mostly proton "plum" material with tiny
electron "raisins."
Alpha particle: 2 protons and 2 neutrons (helium nucleus).
Generated by nuclear reaction. Makes good projectile to fire
at very thin metal foil to test plum pudding model.
Show Rutherford expt. (1909)
Electronic Structure
Photoelectric Effect (Hertz; 1887)
Photoelectron Spectroscopy 1913
Atomic Spectroscopy early 1900's
Stern-Gerlach Experiment 1921 (electron spin)
Schroedinger Equation 1926 (Quantum Mechanics). Levels
of Electronic Structure: electron, orbital, subshell, shell.
H vs. other atoms.
Relationship between electronic structure of atoms
and position on Periodic Table. Build some atoms.
The Periodic Table
Rows (periods) are electron shells.
Columns (groups) hold atoms with same valence electron
structure.
Blocks hold atoms with valence electrons in same subshell
configuration.
Element: defined by proton (atomic) number (smaller
number).
Isotope: defined by mass number (total of protons plus
neutrons; larger number).
History: Mendeleev 1871. Consecutive elements were
placed in series of repeating rows based on repeating chemical
behavior (ease of ionization, melting point, reactivity, valences)
so that elements with similar properties were in same columns.
Show alk metals, alk earths,...noble gases.
Ions
In ions charge determined by balance between protons
and electrons.
Metal atoms prefer to lose electrons to make positive
ions (cations). These atoms have low electronegativity. Lie
to left on Periodic Table.
Nonmetal atoms steal electrons making negative ions
(anions). Have high EN's. Lie to right on Periodic Table.
When elements from opposite sides of Periodic Table
combine ions form. Electrons from low EN metal element stolen
by high EN nonmetal element.
Bonding between ions of opposite charge is electrostatic.
Salts formed, usually water-soluble.
Elements of medium electronegativity (ie. carbon) form
covalent bonds and compounds.
Covalent Compounds
Bonding in covalent compounds occurs by neighboring
atoms sharing valence electrons rather than high EN atoms stealing
electrons from low EN atoms to make pairs of ions.
Lewis structures can be used to determine the valence
electron structure (single and multiple bonding, nonbonding lone
pairs) and shapes of covalent molecules.
Do Lewis structures and VSEPR for typical covalent
molecules (BeCl2, BF3,
CH4, H2O, SF4,
XeF4).
Show VSEPR theo. & actual overheads.
Identical atoms bond together with equal sharing of
all bonding electrons. Atoms bonded together having different
EN's give polar bonds (atoms with higher EN get more electrons).
Severe EN differences (ÆEN > 1.5) give ions.
Intermolecular Forces
Polar molecules have electrons unevenly distributed
in different regions of molecule. Regions with excess electrons
have net negative charge and regions with depleted electrons have
net positive charge.
Positive regions from one molecule attracted to negative
regions of others. Molecules stick to one another weakly by electrostatic
attraction.
Hydrogen bonding: depletion of electrons from hydrogen
by attached electronegative atoms gives proton, very unstable.
Hydrogen attached to electronegative atoms seeks out lone pairs,
forming a special kind of weak bond to neighboring molecule called
hydrogen bond (strongest IM force).
Theory
