Humboldt State University ® Department of Chemistry

Richard A. Paselk

Chem 109 - General Chemistry - Spring 2015

Lecture Notes 2: 23 January

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What is Chemistry?

Chemistry is the study of matter and its transformations.

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

 

Measurements

Accuracy and Precision

First we need to define and distinguish between two terms: accuracy and precision. Consider the two targets below:

Images of two targets showing a closely grouped hits vs. a scattered set of hits.

Which target is the work of the better marksman? I would say B, because she always hits nearly the same place - all we have to do to get all of her shots in the center is to adjust her sights. On the other hand, A is scattered all over. Sure he hit the center once, but, on average he needs lots of shots to do it, adjsuting his sights will do us no good!

For the most part, it is more important to be precise, than it is to be accurate, since we can always adjust our instrument, or our data, to bring the results to the proper value.

Exponential or scientific notation

It is often convenient to express numbers in exponential or scientific notation to indicate significant figures, and to just avoid writing the huge numbers of zeros we often run into in the natural world. [examples] See lab book exercises.

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© R A Paselk

Last modified 23 January 2015