Chemists often work with numbers that are exceedingly large or small. For example, entering the mass in grams of a hydrogen atom into a calculator would require a display with at least 24 decimal places, many of which are occupied by placeholder zeroes, whose sole purpose is to hold a decimal place. A system called scientific notation avoids much of the tedium and awkwardness of manipulating numbers with large or small magnitudes by eliminating the placeholder zeroes. In scientific notation, these numbers are expressed in the format that is shown below.
The coefficient must be greater than or equal to 1 and less than 10 (1 ≤ coefficient < 10) and is determined by selecting all of the non-zero digits, 1-9, as well as any significant zeroes, in a given number. A decimal is inserted so that the coefficient falls into the acceptable range. The power is a positive or negative whole number. A positive power is used when the given number is "large," or greater than 1, and a negative power is used when the given number is "small," or less than 1. The numerical value of the power is determined by how many places the decimal must shift from its location in the given number to where it must be inserted in the coefficient . The number 10 is called the base because it is this number that is raised to the power. Although a base number may have values other than 10, the base number in scientific notation is always 10.