1. Review Problem Set 1

2. Plan for this week’s lab Lab syllabus, then sign agreement Check in with your lab partner Safety video Tuesday, IC 420 Section E: 9:00 am, Section F: 1:00 pm

3. Ch 2. Atoms and Elements

4. Substances are composed of extremely small particles called atoms. If, in some cataclysm, all of scientific knowledge were to be destroyed, and only one sentence passed on to the next generations of creatures, what statement would contain the most information in the fewest words? I believe it is the atomic hypothesis (or the atomic fact, or whatever you wish to call it) that all things are made of atoms—little particles that move around in perpetual motion, attracting each other when they are a little distance apart, but repelling upon being squeezed into one another. Richard Feynman

5. Atom Nucleus (Rutherford’s experiment) Electrons (Thomson’s experiment)

7. Atomic Nucleus

8. Nucleus carries positive charges Each electron carries one negative charge Nucleus carries almost all the mass of an atom

9. Atom Nucleus Electrons (each carries a negative charge) Protons (each carries a positive charge) Neutrons (neutral) number of electrons = number of protons = atomic number Atoms are neutral

10. Atoms that have the same number of protons belong to one kind of element.

12. isotopes: same number of protons, different number of neutrons mass of a proton ≈ mass of a neutron >> mass of an electron number of protons + number of neutrons = mass number

13. OR

14. Practice – Complete the table

16. No change occurs inside a nucleus in chemistry Atoms can lose or gain electrons Na − e − → Na + positive ion = cation Cl + e − → Cl − negative ion = anion Mg − 2e − → Mg 2+ O + 2e − → O 2−

17. Practice – Complete the table

20. isotopes: same number of protons, different number of neutrons mass of a proton ≈ mass of a neutron >> mass of an electron number of protons + number of neutrons = mass number

21. 1 H1.6735 x 10 −24 g 16 O2.6560 x 10 −23 g One atomic mass unit (amu) is defined as 1/12 of the mass of a 12 C atom. 12 C atom: 6 protons, 6 neutrons, 6 electrons. 1 amu = 1.6605 x 10 −24 g

22. 1 H1.6735 x 10 −24 g 16 O2.6560 x 10 −23 g 1 amu = 1.6605 x 10 −24 g

23. 23 Mass Spectrometer Tro: Chemistry: A Molecular Approach, 2/e

24. Mass Spectrum of Natural Copper 69.09 % 63 Cu 30.91 % 65 Cu natural abundance: percent of an isotope in nature

25. Mass Spectrum of Natural Copper 69.09 % 63 Cu: 62.93 amu 30.91 % 65 Cu: 64.93 amu Average atomic mass of Cu = ?

26. How to find the average? 1, 1, 1, 1, 2 Average = (1 + 1 + 1 + 1 + 2) / 5 = 1.2

28. Mass Spectrum of Natural Copper 69.09 % 63 Cu: 62.93 amu 30.91 % 65 Cu: 64.93 amu Average atomic mass of Cu = ? 63.55 amu listed in the periodic table

30. 35 Cl34.967 amu75.78 % 37 Cl36.966 amu24.22 % Average atomic mass of Cl = 34.967 amu x 75.78 % + 36.966 amu x 24.22 % = 35.45 amu listed in the periodic table

31. mass of a proton ≈ mass of a neutron ≈ 1 amu mass number of an isotope ≈ atomic mass of the isotope in amu 35 Cl34.967 amu 37 Cl36.966 amu

32. One atomic mass unit (amu) is defined as 1/12 of the mass of a 12 C atom. The number of carbon atoms in exactly 12 g of 12 C is called Avogadro’s number: 6.022 x 10 23 One Avogadro’s number of particles is called a mole. 1 mol = 6.022 x 10 23 particles 1 pair = 2 particles 1 dozen = 12 particles (exact number)

33. Example 2.6 Calculate the number of atoms in 2.45 mol of Cu. 1 mol = 6.022 x 10 23 particles

34. For Practice 2.6 A pure Ag ring contains 2.80 x 10 22 Ag atoms. How many moles of Ag atoms does it contain? 1 mol = 6.022 x 10 23 particles

36. Experiment 2 next Tuesday Read the lab manual before coming. Bring lab manual, data form, and goggles. Dress properly according to the syllabus. Aprons not required for this experiment.

37. For an element A, its atomic mass is x amu. What is the mass of 1 mol of A in grams? The mass of 1 mol of A is x g. The molar mass of an element is the mass in grams per mole of the element. Unit: g/mol

38. From the definition of molar mass: (recall d = m/V)

39. 1 mol = 6.022 x 10 23 particles Unit: g/mol molar mass and Avogadro’s number are exact numbers

40. By using these two equations, we can (1)Find the number of atoms of an element from its mass.

41. A piece of Cu has a mass of 200. g. How many Cu atoms are present? 1 mol = 6.022 x 10 23 particles

42. A silicon chip has a mass of 5.68 mg. How many silicon atoms are present in the chip? 1 mol = 6.022 x 10 23 particles

43. By using these two equations, we can (1)Find the number of atoms of an element from its mass. (2) Find the mass of a number of atoms in grams.

44. Compute the mass in grams of a sample of six mercury atoms. 1 mol = 6.022 x 10 23 particles

45. Calculate the mass of a sample of cobalt (Co) containing 5.00 x 10 20 atoms. 1 mol = 6.022 x 10 23 particles

46. By using these two equations, we can (1)Find the number of atoms of an element from its mass. (2) Find the mass of a number of atoms in grams. (3) Identify an element.

47. The mass of 500 atoms of an element is 2.24 x 10 −20 g. Identify this element. 1 mol = 6.022 x 10 23 particles

48. Problem Set 2