How Big is an Atom?

• Typically about 0.0000000001 m long

• 1 atom of Cu weighs0.000000000000000000000000233 lb

• These are cumbersome numbers – One useful tool to use when writing numbers

containing lots of zeroes is SCIENTIFIC NOTATION

Scientific Notation

• number is written with one digit in front of the decimal and then it is multiplied by some factor of 10 to make it the correct size one number in front of decimal

x 10some number gives size of number

• Size of atom in scientific notation is– 1 x 10-10 m– 2.33 x 10-25 lb

Units

• Measurements really have two parts– number and a unit

• Without unit, measurement is meaningless– 10 long– is it big, or is it small? – don’t know unless you know the standard it

was measured against

Unit Matters

• With a different unit, number can be VERY different

• CHANGING THE UNIT of a measurement may be useful

• The size of the atom can be written as– 0.1 nanometer or 0.1 nm– Instead of 0.00000000001 m

Units or Standards of Measurement

• What is a nanometer? • First, let’s consider what a kilogram is.

(You’ve heard of it, right?)• Kilo is metric prefix that means 1000• So a kilogram is 1000 grams• Metric prefixes may be used with anything…a

kilomile would be 1000 miles• May use different units to measure same

quantity…must ID that unit!!!

The Metric Prefixes

Prefix Abbreviation Meaning

Mega M 106

kilo k 103

deci d 10-1

centi c 10-2

milli m 10-3

micro 10-6

nano n 10-9

pico p 10-12

What is a nanometer?

• 1/(100000000) of a meter

• Remember, a typical atom is about 0.1 nm in diameter

• HENCE the term nanoscale for molecules and atoms

Dimensional Analysis or Factor Label

• Method of changing units that eliminates the question of “do I multiply or do I divide”

• Showing your units in the calculation answers this question for you

Dimensional Analysis or Factor Label

• Figure out what two things are equal – (find the useful relationship)

• Create the two factors – (that are equal to 1)

• Multiply what you have to start with by the factor that eliminates the unit you don’t want anymore and leaves you with the unit you do want!!

Factor-Label Examples

• If you have 108 eggs, how many dozen do you have?

• How many picometers are there in 2.5 x 10-10 m ?

• If an object has a mass of 243 mg, what is its mass in kilograms?

• Hershey packet– Ans Pbm 1: 2.81 x 105 g/min– Ans Pbm 2: 214 wt oz / qt– Ans Pbm 3: 9.8 x 10-5 g ethanol