Progress in chemistry and other sciences depends in large part on precise and accurate measurements. Scientific measurements are made in the internationally used SI system. Related units commonly used are the meter, the liter, and the gram. Prefixes are used to identify smaller and larger units.
The mass of an object is preferred to its weight, for mass is independent of gravity. Measurements must be precise (reproducible) and accurate. Eponential notation is used to indicate the degree of accuracy and the number of significant digits in the measurements, particularly in reporting very large or very small numbers. The results of calculations based on measurements must reflect the number of significant digits in the measurements.
Calculations often involve the use of conversion factors that relate one propery to another - for example, density - or one unit to another -for example, feet to meters. Density, which relates the mass of a sample to its volume, is a property usefull in identifying the composition of the sample.
Energy, the ability to do work, is measured in joules or calories. Temperature, which is energy-related, can be measured on three different scales - Kelvin, Celsius, and Fahrenheit. The temperature at which under normal conditions a substance melts or boils is a physical property useful in identifying substances. Specific heat reports the amount of enery required to change the temperature of 1 gram of a substance by 1 degree Celsius.