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Physical Quantities

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    Chemistry is a quantitative science. Amounts of substances and energies must always be expressed in numbers and units (in order to make some sense of what you are talking about). You should also develop a sensation about quantities every time you encounter them; you should be familiar with the name, prefix, and symbol used for various quantities.

    However, due to the many different units we use, expression of quantities is rather complicated. We will deal with the number part of quantities on this page, using SI Units.

    are expressed by eXXX or EXXX.

    Words          Number               Prefix  Symbol Exponent
    -----         --------------------- ------  ------ -of 10--
    Quindrillion  1,000,000,000,000,000                  e15
    Trillion          1,000,000,000,000 Tera-    T       e12
    Billion               1,000,000,000 Giga-    G       e9
    Million                   1,000,000 Mega-    M       e6
    Thousand                      1,000 Kilo-    k       e3
    Hundred                         100
    Ten                              10
    One                               1
    Tenth                           0.1 Deci-    d
    Hundredth                      0.01 Centi-   c
    Thousandth                    0.001 Milli-   m       e-3
    Millionth                  0.000001 Micro-   u (mu)  e-6
    Billionth               0.000000001 Nano-    n       e-9
    Trillionth           0.000000000001 Pico-    p       e-12
    -----         --------------------- ------  ------ -------

    By now, you probably realized that every time the number increases by a factor of a thousand, we give a new name, a new prefix, and a new symbol in its expression.

    Reading Numbers

    After you are familiar with the words associated with these numbers, you should be able to communicate numbers with ease. Consider the following number:


    In words, this 18-digit number takes up a few lines:

    One hundred twenty three quindrillions, four hundred fifty six trillions, seven hundred eighty nine billions, one hundred and one millions, two hundred and thirty four thousands, five hundred and sixty seven.

    If a quantity makes use of this number, the quantity has been measured precisely. Most quantities do not have a precise measurement to warrant so many significant figures. The above number may often be expressed as 123e15 or read as one hundred twenty three quindrillions.

    There are seven basic quantities in science, and these quantities, their symbols, names of their units, and unit symbols are listed below:

          == Basic Quantity ==  ==== Unit =====
                Name    Symbol  Symbol Name
          ============= ======  ====== ========
                 Length    l       m   meter
                   Mass    m      kg   Kilogram
                   Time    t       s   Second
       Electric current    I       A   Ampere (C/s)
            Temperature    T       K   Kelvin
    Amount of substance    n     mol   Mole
     Luminous intensity    Iv     cd   Candela
          ============= ======  ====== ========

    *The unit ampere, A, is equal to Coulombs per second, (A = C/s).

    Contributors and Attributions

    Physical Quantities is shared under a CC BY-NC-SA 4.0 license and was authored, remixed, and/or curated by LibreTexts.

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