1  Fundamentals of Chemistry

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1.2 Molecules

1.3 Measurements

1.6 Conversions

1.11 Stoichiometry

1.15 Nomenclature

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measurements

SI Units

# Measurement

It's really not science if your not evaluating and measuring something. We love our measurements and we must all agree on certain standards to help us communicate quantities. There are lots and lots of units that are out there in the wild. One thing you should definitely be able to do after this course is to do any type of unit conversions. This is a real life skill and you can put that on your to do list: Know how to do unit conversions! This is really a big thing with us science types.

We get our standards from the International System of Units - known more commonly as SI Units. There is a rather simple set of seven standard units that we call the fundamental or base SI units. All other units can be traced back to some combination of these seven standard units. Know them. These overlap well with the metric system of units as well. Let's list them and what they measure.

### Table of the Seven Fundamental/Base SI Units

propertysymbol
in formulas
unit nameunit abbreviation
mass$$m$$kilogramkg
length$$\ell$$meterm
time$$t$$seconds
electric current$$I$$ampreA
temperature$$T$$kelvinK
amount of substance$$n$$molemol
luminous intensity$$I$$candelacd

You are always free to explore this subject in more detail on wikipedia or even on OpenStax. And if that wasn't enough, check out the NIST site about these important base units. And by the way, NIST stands for the National Institute of Standards and Technology. Oh, and if you really want to geek out, check out the NIST SI-Redefinition page that tells you even more about how all those base units are now tied to some sort of fundamental constant of nature.

• mass / kilogram kg
• length / meter m
• time / second s
• electric current / ampre A
• temperature / kelvin K
• amount of substance / mole mol
• luminous intensity / candela cd

The Sad Truth It is amazing to think about all the hard work and time spent on coming up with these units and all the derived units base on them. The whole metric system is really based on these units plus prefixes to establish the scale of each unit. This is perfect for doing science. Unfortunately, the good ol' USA likes to remain beholden and entrenched with our historical "english" units. We fought hard for our freedom from England back in the day, but we kept most of their units.

Thanks to our hanging on to these units, we now get to do even more conversions. This includes you! Woo hoo. Twelve inches to the foot, three feet to the yard, five thousand two hundred and eighty feet to the mile. All makes perfect sense, right? Or, how 'bout 2.54 centimeters is an inch. An inch is actually defined as 2.54 cm. Here's a great one... multiply 11 by 7 by 3, what do you get? 231! That is actually a gallon but in cubic inches (in3). Yes, a gallon is 231 cubic inches. Multiples of 10 be damned, the english system had history on its side.

#### Word!

For any and all exams, I do NOT expect you to memorize any set of conversion factors. I will always provide a table of any of the needed conversion factors for working calculations on exams. - Dr. McCord

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