Read Chapters 1 and 2
Chemistry - The study of substances, and in particular, the transformation of substances.
What is a substance?
For now, let's consider a substance to be one of two things:
element - periodic table, composed of the same type of atom.
For instance: see a model of glycine the simplest amino acid (building block of proteins such as hemoglobin )
or a mixture of them
We will return to elements and compounds latter.
Why is Chemistry Important?
The machinery of life
The preservation and destruction of life
Ability to manipulate the world around us
[The practice of science is intended to be value free (i.e. not good or bad). However, value can be applied to what is done with the results of scientific inquiry and also to the problems scientist chose to study and the methods they use]
do scientists approach a problem? - the scientific method
Step 1: Pick a problem: Why can we skate better on ice than on wood?
Step 2: Research: What do we know already? - Some observations:
You can skate on ice well below its
freezing point of 0oC.
Applying pressure to ice causes it to melt (this is unusual).
Make a Hypothesis:
out to be Bill Nye's hypothesis as well, and he constructed the following
diagram to illustrate the idea.
Sounds Reasonable! So we are done!
Reasonable is not enough
An aside - temperature scales, scientific notation, unit conversion
measured on three different scales: Kelvin (K, "absolute temperature
scale", no degree symbol), Centigrade (oC), and Fahrenheit (oF
K = C + 273
Always good to check if an equation seems correct: use values or limits you know: The boiling point (100oC = 212oF) or freezing point (0oC = 32oF ) of water for instance
C = 5 / 9 (212 - 32) = 100
0K - absolute zero - can't
Inconvenient to always write out very large or very small numbers so we use scientific notation:
50000 = 5 * 10000 = 5 *10*10*10*10 = 5x104 (move
decimal 4 places right)
dimensional analysis - factor label
Ex: using the tabulated conversion factor 1 atm = 1.01x105 Pa
Back to our experiment.
The melting point of ice as a function of pressure is given by the following graph:
How much pressure does a skater exert?
Pressure = Force / Area (the smaller the area, the larger the pressure)
The weight of an object is the force it exerts due to gravity.
Need to make assumptions or define our system:
Scientists explanations of things generally only hold for a particular set of parameters - for a particular system. Important to understand what parameters and assumptions were used.
Define the skaters weight and area of the skate:
Given the typical skaters weight (150lb) and the area of a skate blade (20cm2) this corresponds to a pressure of:
x 106 Pascals
Step 5. Draw a conclusion about the
Step 6. Refine the hypothesis and design more experiments to continue testing it.
Theories and Laws
Theory - a physical or mathematical model designed to explain some observation or phenomenon.
Law - a
general statement about a natural phenomenon whose validity is supported by
So why can we skate on ice?
The "little green creature with fire hoses" theory
Theories and hypotheses must: