As we further our study of the science of chemistry, we approach the more quantitative aspect of the science. What I’ve discussed so far has been largely qualitative. But, things from here on out will begin to require more detail and focus, because, well, chemistry is a quantitative science. To help out with this, it is good to have a working knowledge of the rules laid out for us about the use of measurement and significant figures in chemistry.
Know first that measurement is used to compare a physical quantity that is to be measured, with a unit of measurement, or a fixed standard of measurement (Ebbing and Gammon 2009). Measurements are expressed using a number and a unit. The unit lets us know the standard against which the measured quantity is being compared. If this seems confusing to you, like it did to me, Petrucci et al. give a wonderful example of what this means. Say you are measuring a football field using “yards.” Yards is your standard unit of measure. You find that the football field is 100 yards, using a yardstick. What does this mean? This means that the football field as per your measurement is 100 times longer than the standard unit of measure that you used, the yard (Petrucci et al. 2010).
There is a system of measurement that is used throughout the entire scientific world, and it is known as the Système Internationale d’Unités in French, and the International System of Units. In short, the system is abbreviated to SI units. This system is based on the metric system, but is a modernized version of it. Whereas the length of a meter was actually subject to change with changing temperature due to the fact that it was previously defined as 1/10,000,000 of the distance from the equator to the North Pole, this is no longer the case. Now, the length of the meter is unchanging and is reproducible at any given time of year. Now, a meter is defined as the distance traveled by light in a vacuum in 1/299,792,458 of a second.
The SI system contains seven different base quantities. For length, the SI unit is the meter (m). For mass, it is the kilogram (kg). For time, it is the second (s). For temperature, it is the kelvin (K). For the amount of a substance, is the mole (mol). For electric current, it is the ampere (A). And finally, for luminous intensity, it is the candela (cd). Know these SI system units if you don’t already know them. They will forever be a part of your study of the sciences, no matter what the subject. Take it upon yourself to also know SI prefixes for different quantities: 10 to the power of 18 is denoted by the prefix exa (E), 10 to the power of 15 is denoted by the prefix peta (P), 10 to the power of 12 is denoted by the prefix tera (T), etc. (Petrucci et al. 2010). Here, I will not list all of these because these are common knowledge and a quick Google search can tell you all you need to know. In the next post, I will break down some of the more complicated aspects of the SI system.
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