Body

chemistry 100
September 12, 2001

atoms-- as basic unit of matter
parts of atoms -- especially electrons
- ultimate explanation of chemistry
chemical bonds -- links between atoms
sub-assemblies
- molecules
- ions and ionic solids
- nonmolecular bonding (large lattices)
- metals
assemblies
- how molecules collect, form liquids and solids
- how things get big enough to see

What do we actually see and observe
- directly acquired knowledge
- EMPIRICAL observations
  - color, smell, size, firmness
  - will it burn, dissolve, melt
Cataloging Information
- Develop a suitable vocabulary
  - specific field-- specific vocabulary
- Find common features, create categories
Finding Relationships
Empirical Relationship (example #1)
- Heat an object and it gets a little larger
  - seems to be almost universally true

Empirical Relationship #2
- gas (balloon)-- press on it and it gets smaller
- liquid (cylinder) -- press on it and no change
  - vocabulary: compressible, incompressible

Could even become mathematical in form
- Gases P x V = n x R x T
  - a very useful form of a law
  - law need not have an equation

Ideas: what's really behind observations
Initially-- Hypothesis (intelligent guess)
- Could be simple idea
- Could be fairly outrageous, complicated set of ideas
might also call this a theory
- use #1 of the word "theory"
- theory is bit more than hypothesis
Testing Hypothesis
- Look at existing observations--
  - do the known facts fit?
- Make predictions--
  - anything we don't already know
- Perform new observations
- review overlooked observations
- Perform new experiments--
  - test the hypothesis
  - well designed, critical experiments
- Look hard for alternative explanations

support
evidence
acceptance
- theory (proposal, guess, idea)-- use #1 of word
- gets accepted as theory (basis of the field) -- use #2 of the word

These two (contradictory) uses of the word theory allow a lot of intellectually dishonest discussions

we usually prefer the simplest explanation that fits the data
a simple theory with a reasonable fit
- usually prefer to detailed theory with excellent fit
a theory that focuses on some aspect of problem is often favored over a terribly complex universal theory

but... we usually want to know that better theory is there and works even if we operate with the simpler models

Example:

model of atom as tiny solar system
nucleus (sun) and planets (electrons)
planets are populated by intelligent teeny beings
- telepathic (read our thoughts)
- worried about atomic experiments
- decided what we should think
- control the universe to fool us
our science is "wrong"
- it's what they want us to believe
do we reject this as implausible?

Picture of an atom
- first of all, atom is too small to see
- "picture" is a distortion of the word

tiny is a major feature (invisible image)
tiny, distorted (tiny dot or many tiny dots)
- nucleus is home of most of the mass
  - dot in a cloud
  - charged (+) sign
chemistry involves only the outside electrons
- electrons cover a lot of space quickly
- fuzzy cloud, forget the nucleus
- like a balloon (focus on size, shape)

electrons seem to be divided into shells
- mostly energy (can't draw that)
- size (could show that)
- might let circles suggest energies
- (electrons as planets about a sun)

Atoms exist, but are extremely small
Atom is electrically neutral
Atoms of an element are all the same
- simplification: discuss difference later as isotopes
Atom seems to have two parts
- nucleus-- almost all the mass
- nucleus-- positive charge
- charges are multiples of a base unit- +1, +2, +3 ..
- nucleus has 1, 2, 3 ... protons (+ particles)
- also has neutron (about same mass, no charge)
Electrons
- negative region (spread out all over)
- due to negative particles called electrons
  - much lighter in weight
  - equal number
Simplifications:

(ions, bonds, metals / electrical conductivity)