l>Lesson I: The Metric System and SI Units
|IntroductionThe metric device is the wanted system of scientific units for number of reasons:The bulk of countries in the world employ the metric device of measurement.The prefixes attached come metric units bring the same an interpretation for all base units.The metric device is based upon strength of ten, i beg your pardon is practically because:A measurement in the metric mechanism that is stood for by a reasonable number stays a rational numberafter metric unit conversion. (For example, 250 mm = 25 centimeter = .25 m). In comparison irrational unit systems, such as the English system, carry out not have the same residential or commercial property (For example, 250 customs = 20.8333... Ft = 0.0039457... Mile)Because metric units are decimal-based, castle are quickly converted by relocating the decimal point.|
Frequently the above units room too small or more often too big to accordingly scale the measure up quantity. That is then vital to subdivide or expand our measure up unit. This will be disputed in the section on prefixes.
The terms mass and also weight are frequently used interchangebly in chemistry. Strictly speaking, weight is the force (F) linked with a offered mass (m) as it is increased (a) through gravity: F = m × aThe English mechanism unit of mass is the slug, which as soon as multiplied by the acceleration of gravity (32 ft/sec2) gives the weight in pounds.
|Metric base UnitsThe metric mechanism uses the adhering to base units:Unit of MeasurementNameAbbreviation|
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It adheres to from dimensional analysis that 1.0 dm3 = 1.0 L.
|The liter is no the SI unit that volume Volume is a unit derived from length. The volume (V) the a cube that has length (l) = 1.0 cm, broad (w) = 1.0 cm, and height (h) is given by:V = together × w × h = 1.0 cm × 1.0 cm × 1.0 cm= 1.0 cm3By definition, 1.0 cm3 = 1.0 mL ||SI UnitsThe metric-based Système worldwide or SI systems are used to standardize the report or calculation of clinical quantities:|
The SI units are offered to construct all various other units (these are called derived units). Some examples:
Physical QuantityName the UnitAbbreviation
|Amount that 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 united States, words "meter" is assignment "metre" and also the indigenous "liter" is spelled "litre."||Metric Prefixes|
To readjust the range of the base units, prefixes are attached. A prefix represents a factor whereby the base unit should be multiplied. Metric prefixes are detailed below (The prefixes most-commonly used in chemistry are listed in red):PrefixSymbolDecimalValuePower that 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 addition to the basic metric units, plenty of other scientific quantities additionally employ this device 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 can be work to range the base units so the they deserve to represent anything native a very big numeric worth (for instance by making use of prefixes such as Exa, Tera, or Mega) to a very little numeric value (for exampleby using prefixes such together Atto, Femto, or Pico). Scaling the unit increase or down when reporting measurements is an excellent practice because:It can be supplied to keep the numeric value of dimensions to reasonably-sized numbers, say between values of 0.01 come 100.It can be used to remove ambiguous place-holding zeroes in measurments, so that the number of far-ranging figures are appropriately represented.The prefixes instantly convey how many decimal location moves are forced of the numeric value. Because that example, using the clinical notation worth of the metric prefixes):1 centimeter = 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 further explanation that unit interconversion using the metric prefixes as conversion factors, visit the dimensional analysis page. In enhancement to the typical metric prefixes, the Ångstrom is likewise a frequently used unit the arises in measurements on the atom scale:1 Ångstrom = 1 Å = 1 × 10-10 meter|
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