CHM 101 GENERAL CHEMISTRY

FALL QUARTER 2008

Section 2

 

Lecture Notes – 9/24/2008

(last revision: 9/30/08)

 

 

1.1          Overview

  • Macroscopic World: Matter appears to be continuous but infinitely divisible.
  • Microscopic World: Matter consists of individual atoms (from the Greek meaning indivisible).
  • Kinds of Atoms: Relatively few different kinds (100 or so), sort of like letters in an alphabet.
  • Kinds of Substances: A huge number, made of combinations of atoms, sort of like the words in a language.
  • Molecules: More-or-less simple combinations of atoms, example: water (H2O).
  • Molecular vs. Macroscopic Scales: One ounce of water consists of approximately 1024 water molecules.

1.2    Scientific Method

  • Steps in the Scientific Method:
    • 1) Make observations, either qualitative (without numbers), or quantitative (a number and a unit).
      • Qualitative: “The top of the lecture bench is solid.”
      • Quantitative: “The boiling point of water in South Lake Tahoe is 93 °C.”
    • 2) Formulate hypotheses (possible explanations of the observations).
    • 3) Design and perform experiments to test the hypotheses.
    • 1a) Observe the results (sort of like step 1).
    • 2a) Refine the hypotheses.
    • 3a) Design and perform additional experiments, etc.
  • Scientific Models:
    • 1) Formulate a model (also called a theory) from a consistent set of observations and hypotheses.
    • 2) Use the model to predict the outcome of a new experiment.
    • 3) Perform the experiment, comparing the result vs. the prediction.
    • 1a) Reformulate the model to reconcile any differences.
    • 2a) More predictions.
    • 3a) More experiments.
    • 1b) More reformulation of the model, etc.
  • Theory vs. Natural Law
    • Natural Law summarizes behavior (Newton’s Law of Gravity, Einstein’s Law of Relativity)
  • Theory explains observations (Darwin’s Theory of Evolution)

1.3    Units of Measurement

  • A measurement must have both a number and a scale (or unit). For example: a particular measurement might be 50.2 ml.
  • We also need an object. (What is it that we are measuring?) A measurement of 50.2 ml is not very meaningful, unless we stipulate, for example, that it is 50.2 ml of distilled water, or that it is 50.2 ml of concentrated sulfuric acid.
  • Fundamental Physical Quantities
    • Mass
    • Length
    • Time
    • Temperature
    • Electric Current
    • Amount of Substance
    • Luminous Intensity
  • Other quantities, such as Volume, Energy, and Pressure are derived from the fundamental quantities.

  • Systems of Units
    • English (pounds, feet, seconds, degrees Fahrenheit)
    • SI (Systčme International) (kilograms, meters, seconds, Kelvins)

  • We will use only SI in General Chemistry.
  • Prefixes: Just as an inch is a small unit of distance and a mile is a large unit of distance in the English system, SI has ways to describe small and large numbers of its various quantities:

1.4 Uncertainty

  • Uncertainty is a measure of how closely a measurement matches the “actual” value of the quantity being measured.
  • Uncertainty depends on how closely the measuring device can allow an observer to differentiate between different quantities of what is being measured.

  • Certain and Uncertain Digits

  • Uncertainty and the Measuring Instrument

 

Bathroom Scale

Analytical Balance

Grapefruit 1

1.5 lb

1.476 lb

Grapefruit 2

1.5 lb

1.518 lb

 

 

 

 

Pipette

Graduated Cylinder

Water Sample

25.00 ml

25 ml
  • Precision vs. Accuracy