Yocto

In order to increase the precision of realization of the base unit meter, the definition based on the wavelength of a krypton-86 radiation was replaced in 1983 by one based on the speed of light. Also added were the prefixes zetta (Z) for 10, zepto (z) for 10 , yotta (Y) for 10 , and yocto (y) for 10 . 

SI is a decimal system. Fractions have been eliminated, and multiples and submultiples are formed by a system of prefixes ranging from yotta, for 10 , to yocto, for 10 . Calculations, therefore, are greatiy simplified. 

One of the ways we will learn to express quantities in Chapter 1 is by using prefixes such as mega for million (I06), micro for one-millionth (10-6). and atto for 10-18. The illustration shows a signal due to light absorption by just 60 atoms of rubidium in the cross-sectional area of a laser beam. There are 6.02 X 1023 atoms in a mole, so 60 atoms amount to 1.0 X 10-22 moles. With prefixes from Table 1-3, we will express this number as 100 yoctomoles (ymol) or 0.1 zeptomole (zmol). The prefix yocto stands for I0-24 and zepto stands for 10-21. As chemists learn to measure fewer and fewer atoms or molecules, these strange-sounding prefixes become more and more common in the chemical literature. 

Table C Metric Multipliers tera, peta, exa come from tetra, penta, hexa with one letter removed zetta, yotta come from zeta, iota, with one letter added atto comes from Danish "atten" for 18 zepto comes from Latin "septem" or Greek "hepta" (1000 7) and yocto comes from Greek "octo" (1000-8) with one prefix letter added...

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