1. 3.3

2. What makes an atom of one element different from an atom of another element, even though they all contain the same basic three particles – electrons, neutrons, and protons?

3. 3.3 The one defining characteristic of all atoms of the same element is that they have the same number of protons.

4. 3.3 The atomic number = the number of protons This is how the periodic table is arranged. This is also referred to as the Z number of the element. When it is written with the symbol, it is often in subscript. 3 7 Li

5. 3.3 What does the 7 represent? 3 7 Li

6. 3.3 What does the 7 represent? 3 7 Li The atomic mass is the combination of the protons and neutrons. Electrons are discounted because they are so small (1/2000) compared to either a proton or a neutron.

7. 3.3 Complete this chart: SYMBOLATOMIC NUMBER ATOMIC MASS NUMBER OF PROTONS NUMBER OF NEUTRONS NUMBER OF ELECTRONS 6 12 C 18 40 Ar 53 127 I 11 23 Na 22 48 Ti 92 238 U

8. 3.3 What is an isotope?

9. 3.3 An isotope is an atom of the same element (same number of protons) but with a different atomic mass (different number of neutrons). 17 35 Cl and 17 37 Cl are isotopes of each other. 17 protons 17 protons20 neutrons 18 neutrons

10. 3.3 The masses on the periodic table are in amu (atomic mass units). The amu is a relative mass. What is a relative mass?

11. 3.3 The masses on the periodic table are in amu (atomic mass units). The amu is a relative mass. The relative mass of the elements is based on C-12; a very common, stable, and “old” element.

12. 3.3 The average atomic mass found on the periodic table is a weighted average of all the known isotopes of each element. The unit is amu (atomic mass unit).

13. 3.3 Sample 1: Copper occurs as two naturally occurring isotopes, Cu-63 and Cu-65. Respectively, they occur 69% and 31%. Calculate the average atomic mass of copper.

14. 3.3 Sample 2: Silicon occurs as three naturally occurring isotopes, Si-28, Si-29, and Si-30. Respectively, they occur 92.23%, 4.67%, and 3.10%. Calculate the average atomic mass of silicon.

15. 3.3 Sample 3: Silver has an average atomic mass of 107.87 amu, and occurs as two isotopes, Ag-107 and Ag-109. Calculate the percentage occurrences of each isotope.

16. 3.3 Sample 4: Neon occurs as two isotopes, Ne-20 and Ne-22. The average atomic mass on the periodic table for neon is listed as 20.18. What is the abundance of each isotope?

17. 3.3 Because atoms are too incredibly small to actually count, another way of “counting” them was developed. What is this unit?

18. 3.3 The mole is based on the number of atoms in exactly 12.00 g of C-12. This happens to be 6.022 x 10 23 atoms. The mole is the SI unit for the amount of a substance. A mole of something always has the same number of particles, but it may have a different mass, density, volume, etc. The number, 6.022 x 10 23 was named in honor of Amedeo Avogadro who was instrumental in determining this number.

19. 3.3 So exactly how big is a mole? 1 mole of inches is 8 round trips across the galaxy and back. 1 mole of seconds is 954,150 times the age of the universe. 1 mole of blood cells is more than the total number of blood cells of all the human beings on the earth today. 1 mole of pennies would pay off the national debt 86,000,000 times. 1 mole of grains of sand is more than all of the grains of sand on Miami Beach.

20. 3.3 Because we also can’t measure amu’s, we use molar mass to measure atoms, molecules, etc. The mass of one mole of a substance is equal to its atomic mass in grams. 1 mole of helium atoms = 4.00g 5 moles of helium atoms = 20.00g

21. 3.3 Ex 1 3.5 mol C = ___________ g C

22. 3.3 Ex 2 1.6 x 10 24 atoms of Fe = ______________ mol Fe

23. 3.3 Ex 3 27.6 g Ar = __________ atoms Ar

24. 3.3 Ex 4 4.10 mol Ba = _____________ atoms Ba

25. 3.3 Ex 5 1.65 x 10 23 atoms Zn = ______________ mol Zn

26. 3.3 Ex 6 Calculate the number of atoms in 0.40 mol of sulfur.

27. 3.3 Ex 7 If you used 30.6 g of Mg, how many atoms did you use?

28. 3.3 Ex 8 You have a tank of O 2 gas. If the tank contains 5 mol of gas, how many molecules are there? How many atoms are there?

29. CHAPTER 3 TEST  20 multiple choice (3 points each)  20 short answer (1 point each)  2 problems (4 points each)  2 problems (3 points each)  1 problem (6 points) Based on one of the labs from Chapter 3  1 extra credit (3 points)

30. CHAPTER 3 TEST  History of atom – Democritus, Dalton, Thomson, Rutherford  Law of Conservation of Matter  Law of Definite Proportions  Law of Multiple Proportions  Structure of atom Particles, locations, relative charge, relative mass  Isotopes Find e -, p +, n 0 using symbol Atomic number Atomic mass  Average atomic mass Find average atomic mass / find relative abundance  Molar conversions Mass moles Moles particles Mass particles