The SI System of Measurement

The Nature of Measurement Part 1 - number Part 2 - scale (unit) which is the ESSENTIAL part that gives meaning… I say I’ll give you 15. You say… 15 WHAT? (no units!) Examples: 20 grams 6.63 x calories A Measurement is a quantitative observation consisting of TWO parts

Some Fundamental Chem SI Units (le Système International, SI (1800’s France) In science we need ways to express very small amounts of things and large units so we use the PREFIX (written ______) a unit Example: a lot of meters: A tiny weight: before kilometer or km milligram or mg

SI Prefixes Common to Chemistry *A millionth of a meter, the micrometer and nanometer or nm are common bio units! Is there a way to remember these prefixes easily? We can use a visual ladder OR Mnemonic devices Ex. EGBDF (or acronyms)

Metric Ladder! gmL Baseunit decicentimillidekahectokilo Because it is base 10, conversions in the metric system are merely a matter of moving a decimal point. gmL The “base unit” means the you have a quantity (grams, meters, Liters, etc without a prefix. Mnemonic? King Henry Died By Drinking Chocolate Milk

Metric Conversions gmL Baseunit decicentimillidekahectokilo Example #1: Convert 18 liters to milliliters or DA method 18 L liters = milliliters

Metric Conversions gmL Baseunit decicentimillidekahectokilo Example #2: Convert 450 milligrams to grams or DA Method: mg 450 mg = g

Metric Conversions gmL Baseunit deci d centi c milli m deka dk hecto h kilo k Example #3: Convert 20 kilograms to milligrams or DA Method: 20 kg kg = mg PRACTICE!

Metric Temperature Conversions 3 scales we often use for temperature are: 3 scales we often use for temperature are: Celsius called centigrade sometimes, Metric/SI Celsius °C called centigrade sometimes, Metric/SI Fahrenheit (English or American system) Fahrenheit °F (English or American system) Kelvin (metric or SI ‘science’ unit) based on the lowest temperature possible: absolute zero where all kinetic energy is gone. So far impossible to reach. CANNOT GO NEGATIVE! Kelvin K (metric or SI ‘science’ unit) based on the lowest temperature possible: absolute zero where all kinetic energy is gone. So far impossible to reach. CANNOT GO NEGATIVE! Some on reference chart Some on reference chart Celsius to Fahrenheit: °C x (9/5) + 32 = °F. Fahrenheit to Celsius: 5/9 x (°F - 32) = °C Celsius to Kelvin =  C Kelvin to Celsius: °C = Kelvin – 273