Counting Atoms Atoms What is the Atomic Number

Counting Atoms

Atoms • What is the Atomic Number of an element? • What is the Atomic Mass of an element? • What is the difference between average atomic mass and mass number? • Why is the average atomic mass (the one with the decimals) more useful sometimes?

Counting Large Numbers • The astronomical unit (AU or au or a. u. or sometimes ua) is a unit of length approximately equal to the distance from the Earth to the Sun. The currently accepted value of the AU is 149, 597, 870, 691 ± 30 metres (nearly 150 million kilometres or 93 million miles). • Very Large Distance!!!

Scientific Notation Review • • 600000 = 6. 0 x 10 9 467000000 = 4. 67 x 10 8 523000 = 5. 23 x 10 5 Very small numbers 0. 00000072 = 7. 2 x 10 -7 0. 00045 = 4. 5 x 10 -4 0. 001 = 1. 0 x 10 -3

Counting atoms • Atoms are VERY small • How do you quantify such a small substance • Mole: exactly 12 grams of carbon-12 • Molar mass: mass in grams of one mole of an element • Carbon -12 = 12 grams

Counting atoms • 1 mole of any substance posses 6. 022 x 1023 particles • This number Is Avagadro’s Number

Practice • What is the molar mass of 5 elements? • How many particles are in the above amounts? • How many particles are in 1 mol of – Eggs – Pizza slices – Grapes Practice problem B pg 85, 1 -4 Problems C, 13 and a signed “Assignment Report”!!!