SI UNITS AND THE METRIC SYSTEM

SI units are common, agreed-upon units used by scientists all over the world.

Known as the International System of Units

Allow scientists to readily interpret one another’s measurements.

WHAT ARE SI UNITS?

Split into two groups of units: derived and base units.

SI is built upon seven metric units, base units.

Additional units, derived units, are made from combinations of base units.

WHAT ARE SI UNITS?

METRIC PREFIXES

METRIC PREFIXES

A ratio of equivalent measurements that is used to convert a quantity expressed in

one unit to another one.

1km = 1000m

1km = 1 = 1000m 1000m 1km

CONVERSION FACTORS

1,500 km

EXAMPLE

x 1,000 m 1 km

= 1,500,000 m

A way of denoting a number as a product of a number between 1 and 10 and a power

of 10

Scientific notations make working with extremely large and small numbers easier.

SCIENTIFIC NOTATION

To add/subtract in scientific notation, the exponents have to be the same.

(3.0 x  102) + (6.4  x  103);  since 6.4  x  103 is equal to 64.  x  102.  

Now add.

 To multiply, find the product of the numbers, then add the exponents.

To divide, find the quotient of the number and subtract the exponents.

SCIENTIFIC NOTATION

Precision is a gauge of how exact a measurement is.

Accuracy is the closeness of the measurement to the true value.

ACCURACY VS PRECISION

It is important to be honest when reporting a measurement, so that it does not appear

to be more precise than the equipment used to make the measurement allows. We can achieve this by controlling the number of digits, or significant figures, used to

report the measurement.

SIGNIFICANT FIGURES

• Zeros within a number are always significant. Both 4308 and 40.05 contain four significant figures.

• Zeros that do nothing but set the decimal point are not significant. Thus, 470,000 has two significant figures.

• Trailing zeros that aren't needed to hold the decimal point are significant. For example, 4.00 has three significant figures.

RULES FOR SIGNIFICANT FIGURES

When measurements are added or subtracted, the answer can contain no more decimal places than the

least accurate measurement.

When measurements are multiplied or divided, the answer can contain no more significant figures than

the least accurate measurement.

ARITHMETIC WITH SIGNIFICANT FIGURES

150.0 g H2O (using significant figures)

+ 0.507 g salt

150.5 g solution

150.0

* 0.0507

7.605 = 7.61(using significant figures)