(TG) Nov 16: AVOGDRO'S NUMBER; how we count atoms

Avogadro's Number

6.02 x 10^23

• atoms and molechules are extremely small
• macroscopic objects contain too many atoms to count or weigh individually
• Amedeo Avogadro proposed that the number of atoms in 12.000000 grams of Carbon be equal to a constant (one mole of a Carbon)
•  So what is Avogadro's number? Well its 6, 020, 000, 000, 000, 000, 000, 000, 000
• 1 mole = 6.02 x 10^23 atoms
• one mole is simply a multiply of things for example:

1.  pair = 2
2. dozen = 12
3. century = 100
4. mole = 6.02 x 10^23 

The Mole in Perspective

6.02 x 10^23

• So how big is a mole? (in perspective)
• 1 mole of meters would cross the entire galaxy over 3000 times
• 1 mole of smarties would cover 250 planets similar to the size of earth a kilometer deep!
• 1 mole of seconds is 100,000 times greater than the age of the universe
• 1 mole of blood cells more than every human on the face of the earth

A mole is also used to measure the smallest unit of a quantity. For example there is a such thing as a mole of NaCl ions. You do not thing of Na and Cl as separately, but rather as ONE UNIT. 

EXAMPLES:

A sample of  carbon contains 2.4 x 10^25 atoms. How many moles is this?

2.4 x 10^25     x       1 mole

                                    6.02 x 10^23               = 39.9 moles

THINGS TO REMEMBER:

significant figures

the units you want to cancel are always opposite each other (ie. top and bottom)