SECTION 2.1 Units of Measurement. Objective 1. Define SI base units for time, length, mass, and temperature. 2. Explain how adding a prefix changes a.

SECTION 2 .1

Units of Measurement

Objective

1. Define SI base units for time, length, mass, and temperature.

2. Explain how adding a prefix changes a unit. 3. Compare the derived units for volume and

density.

S. I. Units

We measure things everyday and don’t even notice it.

We can use approximations, but scientists need a more exact way.

They need to report data that others can reproduce.

They need a standard set of units for their measurements.

S. I. Units Continued…

In 1795, the French scientists adopted the metric system.

In 1960, an international committee of scientists met up to update the metric system and called it Systeme Internationale d’ Unites, SI.

Base Units

Base Unit: A system of measurement based on an object or event on the physical world.

It is independent of other units.

There are 7 base units in the SI

SI Units

Quantity Base UnitTime second (s)Length meter (m)Mass kilogram (kg)Temperature kelvin (K)Amount of substance mole (mol)Electric current amphere (A)Luminous intensity candela (cd)

Time Units is in Seconds (s)The frequency of microwave

radiation given off by a cesium-133 atom.

Many chemical reactions occur in less than a second therefore scientific notation is important.

Prefixes to SI Units

Prefix Symbol Factor Scientific Notation

Example

giga G 1000000000109 gigameter

mega M 1000000 10 6 megameter

kilo k 1000  103 kilometer

hecto h 100  102 hectometer

deca da 10 10 1 decameter

none none 0-base unit  100 meter

deci d 1/10  10-1 decimeter

centi c 1/100  10-2 centimeter

milli m 1/1000  10-3 millimeter

micro μ 1/1,000,000  10-6 micrometer

nano n 1/1,000,000,000  10-9 nanometer

pico p 1/1,000,000,000,000  10-12 picometer

Length Units are in meters (m)

The distance light travels through a vacuum in 1/299,792,458 of a second.

Vacuum: a space containing no matter.

Close in length to a yard.

MassUnits are in kilograms (kg)Mass is a measure of the

amount of matter.Kg defined by the platinum-

iridium metal cylinder kept in France.

1 kg≈2.2 lbs.We use grams (g) or

milligrams (mg) most of the time in our experiments.

Derived Units

A unit that is defined by a combination of base units

Multiple units to make up the derived units. Examples

Speed=meters/second Volume=meters*meters*meters Density=mass/volume

Volume (m3)

The space occupied by an objectm3 represented by a cube whose sides are all

one meter in length.We will use cm3 for solids with regular

dimensions.Metric unit we are used to is the liter 1 (L) = 1 cubic decimeter (dm3) 1 liter ≈ 1 quartWe will normally use milliliters (mL)

Density (g/cm3 or g/mL)

A ratio that compares the mass of an object to its volume.

Property used to identify an unknown sample

D= M/V

Temperature

Hot and cold are relative terms and only refer to qualitative data.

Thermometers allow temperature to be measure quantitatively.

3 major temperature scales Fahrenheit (1724)

German physicist-Daniel Gabriel Fahrenheit Used mainly only in US

Celsius (1742) Swedish Astronomer Anders Celsius Part of the SI system

Kelvin (1894) Lord William Kelvin Part of the SI system Introduced absolute zero concept-no negative temp-nothing colder

than 0 K.

Temperature

Water’s boiling pt:212º F, 100º C,

373.15K

Water’s freezing pt:32º F , 0º C, 273.15

K

Dry ice’s freezing pt:-108º F , -78º C, 200

K

Absolute zero:-459º F, -273º C, 0K

Converting between temperature scales

ºF= 9/5 ºC + 32 OR ºC=5/9 (ºF - 32) K= ºC + 273 OR ºC=K - 273

What is the relationship between K and ºF?ºF= 9/5 (K-273) + 32ºF= 9/5 K – 491 + 32 ºF= 9/5 K – 459 OR K=5/9 (ºF + 459)