Chemistry Essentials for Dummies

Chapter 1. Matter and Energy: Exploring the Stuff of Chemistry

Measuring Matter

Scientists often make measurements, which may include such things as mass, volume, and temperature. If each nation had its own measurement system, communication among scientists would be tremendously hampered, so scientists adopted a worldwide measurement system to ensure they can speak the same language.

The SI system (from the French Systeme international) is a worldwide measurement system based on the older metric system. SI is a decimal system with basic units for things like mass, length, and volume and prefixes that modify the basic units. For example, here are some very useful SI prefixes:

kilo- (k) means 1,000

centi- (c) means 0.01

milli- (m) means 0.001

So a kilogram (kg) is 1,000 grams, and a kilometer (km) is 1,000 meters. A milligram (mg) is 0.001 grams — or you can say that there are 1,000 milligrams in a gram.

Here are some basic SI units and how they compare to the English units common in the U.S.:

Length: The basic unit of length in the SI system is the meter (m). A meter is a little longer than a yard; 1.094 yards are in a meter. The most useful SI/English conversion for length is 2.54 centimeters = 1 inch

Mass: The basic unit of mass in the SI system for chemists is the gram (g). And the most useful conversion for mass is 454 grams = 1 pound

Volume: The basic unit for volume in the SI system is the liter (L). The most useful conversion is 0.946 liter = 1 quart

Suppose you want to find the weight of a 5.0-1b. bag of potatoes in kilograms. The setup would look that this: