Metric System

Metric System

     Developed by the French in the late 1700’s.

Based on powers of ten, so it is very easy to use.

Early units were based on the properties of the Earth and the Earth’s most abundant substance, water Used by almost every country in the world, with the notable exception of the USA.

Especially used by scientists.

How it Works

   A standard is established for a particular type of measurement, such as length or mass.

The standard is divided into 10 smaller and equal portions- each portion is 1/10 of the standard and given a special prefix The new portions are again divided into 10 smaller segments; this continues over and over again

Metric Prefixes

 Subdivisions of the base metric unit are:  deci = 1/10 and is abbreviated d__ and the lowercase letter precedes the abbreviation of the base metric unit  centi = 1/100 and is abbreviated c__  milli = 1/1000 and is abbreviated m__

Prefixes continued

 We can write the prefixes as decimal equivalents or powers of 10 as follows:  deci = 0.1 or 1 x 10 -1  centi = 0.01 or 1 x 10 -2  milli = 0.001 or 1 x 10 -3

Metric Multiples

 Just as we can divide units into 10 smaller pieces, we can combine 10 units  deka = 10 standard units; its abbreviation is da__  hecto = 100 standard units; h__  kilo = 1000 standard units; k__

Length

    Length is the straight line distance between two points.

The Metric System base unit for length is the meter.

It was originally 1 – 10 millionth of the distance from the equator to the North Pole along the meridian through Paris (1/10 000 000) A Platinum-Iridium bar was two lines scribed on it representing one meter

Length continued…

 The original is kept in Paris, France  There are copies around the world and here in the United States, the National Institute of Standards and Technology (NIST), an agency of the Federal government is responsible for its safe keeping

Applying Prefixes to the Meter

  The meter is abbreviated lower case “m” Subdivisions and multiples have the corresponding prefix added to the “m”  1 m = 10 dm;  1 m = 100 cm;  1 m = 1000 mm

More about prefixes…

 Multiples of the meter are handled in a similar manner:  10 m = 1 dam  100 m = 1 hm  1000m = 1 km

Mass

   Mass is the amount of matter that makes up an object.

A golf ball and a ping pong ball are the same size, but the golf ball has a lot more matter in it. So the golf ball will have more mass.

The Metric standard for mass is the kilogram.

Mass continued…

    It was originally the mass of one cubic decimeter of water The standard kilogram is defined as the mass of a cylindrical bar of platinum iridium stored in Paris, France As with the standard meter, copies are found around the world In the US, the NIST has two

Measuring Mass

 We will use a balance scale to measure mass. For example, a Harvard Pan Balance or a Triple-Beam Balance  Object placed on one side; known masses are placed on the other  Electronic balances are commonly used in today’s laboratory

Changes to the Metric System

    Periodically, scientists gather to propose changes to the Metric System Nevertheless, the basic concept of powers of 10 between units is kept The last major set of changes was in the 1960s-70s Resulted in the SI units and a redefining of some standards

SI

 Stands for international standards  Why isn’t it IS then ?

 Comes from the French name

Systeme Internationale d’ Unites

Hence the abbreviation SI

Changes…

  To accommodate an increasing greater need for precision, the meter is now, “the distance traveled by light in a vacuum in 1/299,792,458 second.” For time, a second using the atomic clock is the duration of 9 192 631 770 periods of radiation from a cesium atom

Other changes…

 Additional prefixes have been added:  micro, μ__, 1 millionth or 1 x 10 -6  nano, n___, 1 billionth or 1 x 10 -9  pico, p__. 1 trillionth or 1 x 10 -12  Mega, M__, million times or 1x10 6  Giga, G__, billion times or 1x10 9  Tera, T__, trillion times or 1x10 12

Commonly used prefixes in Chemistry

 kilo  deci  centi  milli  micro  nano  pico-

Biggest Change



Established 7 basic standard units to be used and from which all others are derived

Standard SI Units

       Length = Meter (m) Mass = Kilogram (kg) Time = Second (s) Temperature = Kelvin (K) Amount of Substance = Mole (mol) Electric Current = Ampere (A) Luminous Intensity = Candela (cd)

Still use prefixes…

 For example:     1 milliampere (1 mA) is one thousandth of an Ampere (A) 1 picosecond (1ps) is one trillionth of a second (s) 1 gigameter (Gm) is a billion meters (m) 1 micrometer (1μg) is one millionth of a meter (m)

Derived Units

 When one or more of the Standard SI Units are combined to give a new measurement unit, that unit is called a derived unit of measurement  Area would be an example because we multiply the length times the width: 15 m x 10 m = 150 m 2

Derived Units…continued

  The m 2 is read “square meters” not meters squared The SI Derived Unit of FORCE is the Newton, abbreviated N and is defined as the mass in kilograms times the acceleration of the object in meters per second each second --- kg, m and s are all SI standard units; therefore, N is a derived unit………………………..simple

Mnemonic



Kangaroos Hop Down Mountains Drinking Chocolate Milk



Kahn’s Hot Dogs Use Dead Cow Meat

How to use the mnemonic

   First letter gives you the starting letter of the prefixes in their correct order When changing between two units you simply count the spaces from starting unit to the desired unit Move decimal point that number of places in the same direction

Example

 Change 15.5 cm to dekameters    Kilo-hecto-deka-unit-deci-centi-milli Starting at centi- you are going to the left three places to deka Therefore you move the original decimal three places to the left giving you 0.015 dam

Volume

    Volume is the amount of space contained in an object.

We can find the volume of box shapes by the formula Volume = length x width x height In this case the units would be cubic centimeters (cm 3 ).

So a box 2 cm x 3 cm x 5cm would have a volume of 30 cm 3

Liquid Volume

   When the metric system was created, they decided that 1 cm 3 of water would equal 1 milliliter of water and the 1 mL of water will have a mass of one gram.

1 cm 3 1 cm 3 of anything = 1 mL of anything water = 1 mL of water = 1 gram

Water Mass and Volume

     1 cm 3 water = 1 mL of water = 1 gram So what would be the mass of 50 mL of water be?

50 grams So what would be the mass of 1 liter of water be?

1 L = 1000 mL so its mass would be 1000 grams or a kilogram.