l>Lesson I: The Metric System and SI Units
|IntroductionThe metric system is the preferred system of scientific units for several reasons:The bulk of countries in the human being employ the metric device of measurement.The prefixes attached come metric units bring the same an interpretation for all base units.The metric mechanism is based upon powers of ten, i m sorry is practically because:A measure up in the metric mechanism that is represented by a reasonable number remains a reasonable numberafter metric unit conversion. (For example, 250 mm = 25 cm = .25 m). In contrast irrational unit systems, such together the English system, carry out not have the same building (For example, 250 inches = 20.8333... Ft = 0.0039457... Mile)Because metric units room decimal-based, they are quickly converted by moving the decimal point.|
Frequently the above units space too small or more often too big to appropriately scale the measure up quantity. It is then necessary to subdivide or increase our measure unit. This will be questioned in the section on prefixes.
The state mass and weight are regularly used interchangebly in chemistry. Strictly speaking, load is the force (F) connected with a provided mass (m) together it is accelerated (a) by gravity: F = m × aThe English system unit of mass is the slug, which as soon as multiplied through the acceleration of heaviness (32 ft/sec2) provides the load in pounds.
|Metric basic UnitsThe metric device uses the following base units:Unit that MeasurementNameAbbreviation|
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It follows from dimensional analysis that 1.0 dm3 = 1.0 L.
|The liter is no the SI unit the volume Volume is a unit acquired from length. The volume (V) of a cube that has length (l) = 1.0 cm, width (w) = 1.0 cm, and also height (h) is provided by:V = l × w × h = 1.0 cm × 1.0 centimeter × 1.0 cm= 1.0 cm3By definition, 1.0 cm3 = 1.0 mL ||SI UnitsThe metric-based Système global or SI devices are used to standardize the report or calculation of scientific quantities:|
The SI devices are offered to construct all other units (these room called obtained units). Some examples:
Physical QuantityName of UnitAbbreviation
|Amount the Substance||Mole||mol||Electric Current||Ampere||I||Luminous Intensity||Lumen||Iv|
|Velocity||v||m · s-1|
|Force||F||kg · m · s-2||Newton (N)|
|Energy||E||kg · m2 · s-2||Joule (J)|
|Outside the joined States, the word "meter" is spelled "metre" and also the indigenous "liter" is assignment "litre."||Metric Prefixes|
To change the range of the base units, prefixes space attached. A prefix to represent a factor whereby the base unit have to be multiplied. Metric prefixes are listed below (The prefixes most-commonly offered in chemistry are detailed in red):PrefixSymbolDecimalValuePower the Ten
|Giga- ||G||1,000,000,000||109||Mega- ||M||1,000,000||106||Kilo- ||k||1,000||103||Hecto- ||h||100||102||Deka- ||da||10||101||(no prefix)||1||100||Deci-||d||0||.1||10-1||Centi-||c||0||.01||10-2||Milli-||m||0||.001||10-3||Micro-||µ||0||.000001||10-6||Nano-||n||0||.000000001||10-9||Pico-||p||0||.000000000001||10-12||Femto-||f||0||.000000000000001||10-15||Atto-||a||0||.000000000000000001||10-18|
|In enhancement to the basic metric units, numerous other clinical quantities also employ this mechanism of prefixes:||1 Mb = 1 Megabyte = 1 × 106 byte|
|1 Food Calorie = 1 kcal= 1 kilocalorie = 1 × 103 calorie|
|1 ns = 1 nanosecond = 1 × 10-9 second|
|1 pf = 1 picofarad = 1 × 10-12 farad|
|1 kWH = 1 kiloWatt·hour = 1 × 103 Watt·hour||The metric prefixes have the right to be to work to scale the base systems so that they have the right to represent anything native a very huge numeric value (for example by using prefixes such as Exa, Tera, or Mega) to a very little numeric worth (for exampleby utilizing prefixes such together Atto, Femto, or Pico). Scaling the unit increase or down as soon as reporting measurements is an excellent practice because:It have the right to be offered to keep the numeric value of dimensions to reasonably-sized numbers, say between values that 0.01 come 100.It deserve to be offered to remove ambiguous place-holding zeroes in measurments, so the the number of far-ranging figures are appropriately represented.The prefixes soon convey how numerous decimal ar moves are required of the numeric value. For example, using the scientific notation value of the metric prefixes):1 cm = 1 centimeter = 1 × 10-2 meter = 0.01 meter1 kg = 1 kilogram = 1 × 103 gram = 1000 gram1 µL= 1 microliter = 1 × 10-6 liter = 0.000001 literFor more explanation of unit interconversion making use of the metric prefixes together conversion factors, visit the dimensional analysis page. In addition to the conventional metric prefixes, the Ångstrom is additionally a generally used unit that arises in dimensions on the atomic scale:1 Ångstrom = 1 Å = 1 × 10-10 meter|
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