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The Metric System

Mr. Shields Regents Chemistry U00 L03

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In Anglo-Saxon England (before the Norman conquest of 1066) the inch (ynce) was defined to be the length of 3 barleycorns ???barleycorns ???

(Of course we all know how large (Of course we all know how large a barleycorn is right???)a barleycorn is right???)

-A foot = 36 barleycorns = 12 ynce (36/3)

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Area

• 1 acre = size of a field a farmer could plow in 1 day

– Hmmm …

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1790 – French Academy of Sciences created the Metric

System• The unit of length was to be a

portion of the Earth's circumference (the std.)

• Measures for volume and mass were to be derived from the unit of length

• Larger and smaller multiples of each unit were to be created by multiplying or dividing the basic units by 10 i.e decimal system.

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Since 1875 the United States has subscribed to the International System of Weights and Measures, the official version of the Metric System.

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Length

The fundamental unit of lengthlength was named the meter.

What is a meter?

originally defined as “1/10,000,000th of the distance from the Equator to the North Pole measured along the meridian that runs through Dunkirk, France.”

currently defined as the “distance a beam of light travels in 1/299,792,458 of a sec.”

– That’s 1 / speed of light– which is also exactly 39.37 inches.

Metric Prefixes

Prefix Symbol Value Power Example

mega M 1,000,000 106 megaton

kilo k 1,000 103 Kilometer or kilogram

deci d 0.1 10-1 decimeter

centi c 0.01 10-2 centimeter

milli m 0.001 10-3 Millimeter or milliliter

micro 0.000001 10-6 micron

nano n 0.000000001 10-9 nanotechnology

giga G 1,000,000,000 109 gigabyte

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Mass

The Fundamental unit of mass is the Kilogram (Kg)(Kg)

Defined as the mass of one cubic decimeter (0.1m x 0.1m x 0.1m) of water

*What is a kilogram?

The fundamental S.I. unit for mass is the kilogram. It’s defined as the mass of 1 dm3 (1 liter) of water at 4°C.

1 dm

1 dm

1dm

Recall…1 dm = 0.1m or 10 cm

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Volume

The S.I unit for volume is the m3

• This is a derived unit. Derived units are obtained by multiplying or dividing Basic units (in this case length)

What is a Liter?

A common unit used in volume measurement is the liter.

The Liter was defined as

a cube measuring 1 decimeter on each side, i.e. 1 dm3, or in cm it’s 1000 cm3.

1 dm

1 dm

1dm So how much does a

liter of water weigh?

What is a kelvin?

The S.I. unit for temperature is the kelvin

A difference of 1 degree kelvin (K) and 1 degree Celsius (°C) is exactly the same size (1 deg K = 1 deg C)

To convert:°K = °C + 273.15

The kelvin is based on absolute zero (the coldest temperature possible.)

*What is a second?

The Fundamental S.I. unit for time is the second. It was originally defined as 1/86,400th of the average solar day.

It’s now defined using some large number of atomic vibrations of the Cs-133 atom.

– Basis of the “Atomic Clock”

What is a mole?

The fundamental SI unit for counting is defined as 6.023 x 1023 of anything

We’ll discuss this important concept at a later time

The Mole !

There are 7 fundamental units in the SI System

Quantity Unit name Abbreviation

length meter m

mass kilogram kg

temperature Kelvin (not Centigrade)

K

time second s (or sec)

amount mole mol

The Ampere (A) and the Candela (cd) are the other 2

Derived Metric Units

There are several other important units used for volume measurement

- Milliliter and liter (1dm3)– 1 liter (l) = 1000 milliliter

(ml)– 1 ml = 0.001 L = 1 cm3

(sometimes referred to as “cc” in the medical field)

– So … 1 Liter = how many cm3 and how many ml?

A combination of several fundamental units

Other Key Derived Metric Units

The JOULE

– Unit of ENERGY– Ex. Heat, Kinetic & Potential Energy

Comparable to the calorie

The PASCAL

– Unit of PRESSURE– Force/area – Ex. Atmospheric and gas pressure

Comparable to mm or inches of Hg