2. isotope Are atoms of the same element that have different masses. Due to a different number of neutrons in the nucleus.

3. Nuclide Is a general term for any isotope of any element.

4. Atomic number Represented in mathematical equations by the letter Z in the book examples. Remember. The number of protons is represented by the atomic number, and will never change. It is the “fingerprint” of the element.

5. Mass number Is the total number of protons and neutrons in the nucleus of an isotope. The neutron and the proton mass values are each approx 1. The periodic table reports the average atomic mass of the many nuclides of a particular atom

6. Atomic mass unit The mass of atoms is extremely small. Therefore, we use relative atomic masses because it is easier to do calculations. Arbitrarily chose a standard and assigned a relative mass value. Selected the carbon –12 nuclide.

7. Atomic mass unit or amu Carbon -12 has been assigned the relative value of 12 amu. Or 1 amu is exactly 1/12 th the mass of a carbon-12 atom ( nuclide) Mass of any nuclide is compared to the carbon –12 nuclide An atom that is 4x the mass of the carbon- 12 atom will be 4 x 12 amu = 48 amu.

8. continued An atom that is 2/3 the mass of the carbon- 12 atom will have a mass of 2/3 x 12 amu = 8 amu.

9. Finding average atomic mass Multiply the abundance factor, (%), by the mass number of the isotope Add up all the isotopes Divide by 100

10. example Neon has two isotopes Ne-20 has a mass of 19.992 amu and occurs in nature 90% of the time. Ne-22 has a mass number of 21.991 amu and occurs 10% of the time. ((90 x 19.992) + (10 X 21.991) ) / 100 = 20.192 amu

11. How many in a dozen? How many in 2 dozen If you have 36 shoes, how many dozen?

12. Mole The chemist dozen Instead of 12 units of something it is 6.02 x10 23 units of something. 6.02 x 10 23 is called Avogadro’s number –Or the number of particles in exactly one mole of a substance.

13. Molar mass The mass of one mole of a substance. Units are g/mol Numerically equal to the atomic mass listed on the periodic table. The molar mass of an element contains one mole, or 6.02 x10 23 atoms of that element.

14. conversions He has a molar mass of 4.00 g/mol How many grams of He are there in 5 moles? 4.00 g/mol x 5 mol = 20 grams Note: the mole unit crosses out.

15. problem How many grams will there be in 4 moles of oxygen?

16. again How many grams are there in 4.5 moles of copper? Page 83 sample problem 3-2 1,2,3,4

17. Now the other way Given the grams calculate the moles. You have 72 grams of copper, how many moles do you have? 72 grams / 63.55 g/mol = 1.13 moles of Cu Page 83 sample problem 3-3 1,2

18. How many moles is a given # of atoms? If you have 2.0 x 10 23 atoms of Ca, how many moles do you have. 2.0 x 10 23 atom Ca x 1 mol Ca/6.02x 10 23 atom of Ca = 0.33 mol Ca Page 84 sample problem 3-4 1,2,3

19. Given # atoms find the mass Find the mass of 5 x 10 16 atoms of copper. 5 x 10 16 atoms Cu x 1mole/6.02x10 23 atoms multiplied by 63.55 g/mol = 1.31 x 10 -9 Page 85 practice problem 3-5 1,2,3