Unit 4Measurement – Basic Units

•The International System of Units (SI) (1.10)

•Current definitions of the seven base SI units

•Review of exponential notation (Appendix A-1)

•Metric prefixes and their interconversion (1.10)

What is Chemistry? (Intro to Chapter 1)

• Matter – anything that occupies space and has a mass (1.8)

• Chemistry – the study of matter and its transformations (Introduction to Chapter 1)

The SI System (1.10)• Adopted in 1960 – states standard units to be used in

measurement of seven basic properties as given below.

Physical Quantity

Name of Unit Symbol of Unit

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

Current Definitions of the Seven SI Units

• Six have very well defined, though somewhat abstract, descriptions. For example,– second: The second is the duration of 9 192 631 770 periods of

the radiation corresponding to the transition between the two hyperfine levels of the ground state of the cesium 133 atom.

– meter: The meter is the length of the path travelled by light in vacuum during a time interval of 1/299 792 458 of a second.

• Definitions of the other four that have precise definitions may be found at http://physics.nist.gov/cuu/Units/current.html

• The kilogram is the only one not precisely defined – see next slide.

The Kilogram

• The kilogram is called a prototype standard – there is one chunk of matter that is “the” kilogram as pictured.

States of Matter (1.9)

• Three common states of matter (plus a bonus):– Gas – takes shape of container, flows easily,

compressible– Liquid – takes shape of container but with a flat

top, flows easily, not very compressible– Solid – retains shape, does not flow

appreciably, not very compressible– (A bonus state: plasma – a stream of charged

particles – this is the stuff of plasma TV)

Review of Exponential Notation (Appendix A-1)

• Looking at the SI base units gives a strong sense that it is a metric-based system

• The metric system depends heavily on the ability to maneuver the decimal point in a number

• Some of the numbers we will see during the semester are incredibly large or incredibly small and we must have a system to write and work with these numbers without difficulty

• Thus there is a need to be conversant in exponential notation

Review of Exponential Notation (Appendix A-1)

• The concept of exponential notation is based on our base 10 number system:

• In the left column, where the numbers are greater than 1, the power on 10 is the number of decimal places to the right of the digit “1”

• In the right column, where the numbers are less than 1, the exponent on 10 is negative and is the number of decimal places from the original decimal place to that just after the digit “1"

1 1

2 2

3 3

110 10 0.1 10

101

100 10 10 10 0.01 1010 10

11000 10 10 10 10 0.001 10

10 10 10

Examples of Converting Between Standard Notation and Exponential Notation

• Consider the following conversions:

63410 m = 6.3410 x 104 m

145.6 s = 1.456 x 102

0.00389 kg = 3.80 x 10-3 kg

9.87 x 104 L = 98700 L

5.12 x 10-5 cm = 0.0000512 cm

Metric Prefixes (1.10)•Part of the beauty of the metric system is that interconversions are simply a matter of moving the decimal point. Metric prefixes are used to indicate the size of the unit. Some of the more common metric prefixes are given in the table below.

Prefix Exponential Expression

Abbreviation

tera- 1012 T

giga- 109 G

mega- 106 M

kilo- 103 k

Base Unit 100 -

deci- 10-1 d

centi- 10-2 c

milli- 10-3 m

micro- 10-6 μ

nano- 10-9 n

Metric Conversions

• Notice in the table:– The difference in exponents

between two prefixes gives the number of decimal places to be moved in a conversion

– If the conversion is from a larger unit to a smaller unit (down the table), the decimal point is moved to the right

– If the conversion is from a smaller unit to a larger unit (up the table), the decimal point is moved to the left

– See examples on the next page

Prefix Exponential

Expression

Abbreviation

tera- 1012 T

giga- 109 G

mega- 106 M

kilo- 103 k

Base Unit 100 -

deci- 10-1 d

centi- 10-2 c

milli- 10-3 m

micro- 10-6 μ

nano- 10-9 n

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Examples of Metric Conversion

Prefix Exponential Expression

Abbreviation

tera- 1012 T

giga- 109 G

mega- 106 M

kilo- 103 k

Base Unit 100 -

deci- 10-1 d

centi- 10-2 c

milli- 10-3 m

micro- 10-6 μ

nano- 10-9 n

42600 m = 42.6 km(m to km is three decimal places, since going up the table move three decimal places to the left)

0.459 km = 45900 cm(km to cm is five decimal places, since going down the table move five decimal places to the right)

350 mL = 0.350 L(mL to L is three decimal places, since going up the table move three decimal places to the left)

4.52 x 1034 ds = 4.52 x 1035 cs(ds to cs is one decimal places, since going down the table move to the right making the exponent bigger by one)