![]() The initial units of the metric system, which eventually evolved into the SI system, were established in France during the French Revolution. Need a refresher or more practice with scientific notation? Visit this site to go over the basics of scientific notation. Units for other properties may be derived from these seven base units. SI units have been used by the United States National Institute of Standards and Technology (NIST) since 1964. The standards for these units are fixed by international agreement, and they are called the International System of Units or SI Units (from the French, Le Système International d’Unités). The measurement units for seven fundamental properties (“base units”) are listed in Table 1.2. Not only will this be confusing to the medical professional giving the dose, but the consequences can be dire: 100 mg given three times per day can be effective as an anticonvulsant, but a single dose of 100 g is more than 10 times the lethal amount. Suppose a doctor prescribes phenobarbital to control a patient’s seizures and states a dosage of “100” without specifying units. Without units, a number can be meaningless, confusing, or possibly life threatening. The meat used to prepare a 0.25-pound hamburger weighs one-fourth as much as the accepted weight of 1 pound. A 2-liter bottle of a soft drink contains a volume of beverage that is twice that of the accepted volume of 1 liter. Units, such as liters, pounds, and centimeters, are standards of comparison for measurements. The mass of the average mosquito is about 0.0000025 kilograms, which can be written as 2.5 × × 10 −6 kg. (Scientific notation is also known as exponential notation a review of this topic can be found in Appendix B.) For example, the maximum takeoff weight of a Boeing 777-200ER airliner is 298,000 kilograms, which can also be written as 2.98 × × 10 5 kg. The number in the measurement can be represented in different ways, including decimal form and scientific notation. While the number and unit are explicitly represented when a quantity is written, the uncertainty is an aspect of the measurement result that is more implicitly represented and will be discussed later. Every measurement provides three kinds of information: the size or magnitude of the measurement (a number) a standard of comparison for the measurement (a unit) and an indication of the uncertainty of the measurement. ![]() Measurements provide much of the information that informs the hypotheses, theories, and laws describing the behavior of matter and energy in both the macroscopic and microscopic domains of chemistry. Perform basic unit calculations and conversions in the metric and other unit systems.Describe the properties and units of length, mass, volume, density, temperature, and time.Identify the three basic parts of a quantity.By the end of this section, you will be able to:
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