Chemistry is the study of matter and its transformations.

• "Classical" chemistry involves mostly electron transfers and/or interactions of charges (electron and nuclear). As we'll see only some electrons in atoms are involved - the outer or valence electrons of atoms.

• Nuclear chemistry is an extension of chemistry where nuclei are transformed changing one kind of atom (element or isotope) to another. This is a completely separate realm of phenomena, largely unimportant in everyday life (unless you work at a nuclear power plant!).

More specifically, chemistry is the scientific study of matter. So what do we mean by science? Two common "definitions":

• The body of knowledge and rules/laws/theories we have discovered regarding the natural world.

• The method of discovery and confirmation used by scientists. Classically we describe this process as the "Scientific Method" summarized in the steps below:

  • Identify a problem based on initial observations

  • Collect data via planned Observations and/or Experiments ("asking nature a question")

    • "Clean" simple experiments vs. statistical inference

    • Controls - everything the same except the variable of interest.

  • Analyze and Evaluate results

  • Hypothesis

  • Theory (model)

    • Law

Matter

What is matter? Stuff. Has mass and occupies space.

Mass: The measure of quantity for matter. Mass is the property of matter resulting in its inertia and and attraction via gravity.

• Do not confuse mass and weight. Weight is the force acting on an object due to gravity.

intensive properties

• Physical properties of substances can be observed without, in principle, changing their compositions.

States of Matter. Matter can exist in three states under earth-surface conditions:

• Solid: definite shape and volume (Crystals vs. super-cooled liquids or glasses)

• Liquid: definite volume, but no defined shape - will fit to container etc.

• Gas: no definite shape or volume - will fill whatever container they are in.

  • both liquids and gases are fluids.

• Chemical properties of substances describe behaviors which lead to changes in composition.

Measurements

Accuracy and Precision

Exponential or scientific notation

Significant Figures

Significant Figures and Calculations: Two basic sets of rules:

1. Addition/Subtraction rule: Significant figures are determined by looking at the decimal place of the numbers being added or subtracted. The number with the "least decimal places" determines the decimal place of the answer, e.g. if we add 1,216,956 to 214.879, the first number has the fewest decimal places, so the answer is rounded off to the 1's place: 1217170.879 goes to 1217171.

1. Multiplication/Division rule: In this case we count the digits. The number with the fewest significant digits determines the number of significant digits in the answer.

   • Note that in this case we are looking at how the error propagates as a fraction of the total (% error), for example

     • for the problem 2.0 x 201 = 402 should be written as 4.0 x 10².

     • This can be understood by doing the problem with upper and lower ranges of the measured number: 1.95<2.0<2.05

       • 1.95 x 201 = 391.95

       • 2.05 x 201 = 412.05

© R A Paselk

Last modified 27 August 2009