1. Bellwork 2/2 1.What is the main idea of Dalton’s Atomic Theory. 2.Why was Dalton’s theory successful? 3.Compare Thomson’s atomic model with Rutherford’s atomic model. 4.What did Thomson achieve with the cathode ray tube experiment? 5.How did the gold foil experiment lead to the conclusion that the atom has a positive nucleus? 6.What did James Chadwick discover?

2. Bellwork 2/8 1. Why do scientists use moles as a counting unit? 2. What is Avogadro's number? 3. How many particles are in 1 mol of iron?

3. Chapter 4 Atoms Section 2: The Structure of Atoms

4. Learning Targets: What is the difference between protons, neutrons and electrons? What do atoms of an element have in common with other atoms of the same element? Why do isotopes of the same element have different atomic masses? What unit is used to express atomic mass?

5. What is in an atom?? Atoms are made up of various subatomic particles. We will learn about the 3 biggies: protons, neutrons and electrons.

6. The three main subatomic particles are distinguished by mass, charge and location in the atom. Check the next chart and fill in yours…

7. Subatomic particles Particle/Charge Mass (kg) Location in the atom Proton +1 same as neutronin the nucleus 1.67 × 10 -27 Neutron 0 same as protonin the nucleus 1.67 × 10 -27 Electron –1 smaller than p+ and n 0 outside the nucleus 9.11 × 10 -31

8. I want to show you something really cool to help you visualize what kind of size we’re talking about here… http://htwins.net/scale2/

9. Each element has a unique number of protons!

10. As you move across the periodic table, this pattern continues. Each element has a unique number of protons. In fact, an element is defined by the number of protons in an atom of that element.

11. Most atoms are neutral in charge. Why is that, I hear you beseechingly ask? Well, most atoms have an equal number of protons and electrons and those charges cancel out.

12. For example, a helium atom has 2 protons and 2 electrons. That makes it neutral, right? Right! The 2 +’s cancel out the 2 –’s. (See below.) Charge of 2 protons: +2 Charge of 2 neutrons: 0 Charge of 2 electrons: -2 Total charge: 0

13. What happens if an atom gains or loses an electron?? Then we have something different going on. If an atom gains or loses an electron, it becomes charged and now it has a new name: an ion. An ion is an electrically charged atom or group of atoms formed by the loss or gain of one or more electrons

14. An electric force holds the atom together. It’s the ol’ positive and negative attraction. Protons are positive and electrons are negative and they are attracted to each other. In fact, this electric force holds the atom together. On a larger scale, this same force holds solid and liquid molecules together… like a water molecule.

15. Atomic Number and Mass Number Atoms of each element have the same number of protons, but they can have different numbers of neutrons.

16. Take 3! Questions, that is. 1. What is an atom called that has different numbers of electrons? 2.How is it formed? 3.Why are most atoms neutral?

17. Take 3! Questions, that is. 1. What is an atom called that has different numbers of electrons? 2.How is it formed? 3.Why are most atoms neutral?

18. Take 3! Questions, that is. 1. What is an atom called that has different numbers of electrons? An ion. 2.How is it formed? Electrons are gained or lost. 2.Why are most atoms neutral? The number of protons equal the number of electrons.

19. Atomic number and Mass Number The atomic number (Z) of an element, tells you how many protons are in an atom of that element. Who knows where to find it on the periodic table? Does anyone know the origin of “Z”?

20. Atomic number equals protons and electrons. If we consider a neutral atom, the number of protons equals the number of electrons. That means the atomic number is also the number of electrons.

21. The atomic number of a given element never changes.

22. Each element is defined by its unique number of protons, so each element has a unique atomic number. Hydrogen has only 1 proton. Its atomic number is… 1! Uranium is the largest naturally occurring element. It has 92 protons. So what is Z??

23. Mass number = total number of p + and n 0 The mass number (A) of an element equals the number of protons plus the number of neutrons in an atom of the element. A fluorine atom has 9 p+ and 10 n 0, so A = 19. An oxygen atom has 8 p+ and 8 n 0, so A=16.

24. The mass number = the number of protons and neutrons (not electrons) because protons and neutrons provide most of the atom’s mass.

25. Atoms can have the same atomic number (p+) but they can have different mass numbers because the number of neutrons can vary.

26. A handy graphic It shows which subatomic particles in the nucleus of an atom make the atomic number and which contribute to the mass number… Atomic number Z = protons (= electrons) Mass number A = protons + neutrons

27. Take 2…! 1. Which can vary for a given element: Protons, neutrons, electrons? 2.Put the following in order from smallest to greatest mass: electron, atom, proton, nucleus

28. Take 2…! 1. Which can vary for a given element: neutrons… and electrons (ions) 2.Put the following in order from smallest to greatest mass: Electron, proton, nucleus, atom

29. Isotopes! So we learned that atoms of a single element can have different numbers of neutrons which gives different mass numbers. An isotope is an atom that has the same number of protons but a different number of neutrons – we’re talking about of the same element.

30. Because they have the same number of protons and electrons, isotopes of an element have the same chemical properties. However, isotopes have different masses. Now… why is that?!

31. Let’s look at the 3 isotopes of hydrogen… Each has 1 p+ and 1 e-. The most common, protium, doesn’t have any neutrons.

32. Take 2… Which hydrogen isotope has the most mass? What is the atomic number of each isotope?

33. The Isotopes of Hydrogen

34. Side note about deuterium: It is a fuel required for nuclear fusion – a potential energy source. Without radioactive waste products. It fuses 2 deuterium atoms and the energy released is greater than the energy released during nuclear fission (uranium).

35. Interesting factoid: Nuclear medicine uses radioactive isotopes to diagnose and treat certain conditions. Some are used to create images like Xrays which radiologists interpret and analyze. Some are used to treat cancer.

36. The radioactive source may be sealed in a capsule and placed directly in a patient’s body near cancerous cells. This is called internal radiation therapy. Because radiation can pass through the body, a person undergoing this type of radiation must stay in the hospital and away from others.

37. Nuclide Symbol or Isotopic Symbol

38. How to calculate the number of neutrons If you know the atomic number and mass number, you can calculate the number of neutrons that an atom has.

39. To find neutrons: Mass number – atomic number = number of neutrons 235 (protons + neutrons) -92 protons = 143 neutrons 39

40. Practice 1: Find the number of protons, neutrons and electrons for: Carbon-14 Nitrogen-15 Sulfur-35 Calcium-45 Iodine-131

41. Practice 1: Find the number of protons, neutrons and electrons for: Carbon-14 – 8 neutrons Nitrogen-15 - 8 neutrons Sulfur-35 – 19 neutrons Calcium-45 – 25 neutrons Iodine-131 – 78 neutrons

42. Atomic Mass You find it on the periodic table and it’s measured in amu’s.

43. Atoms are very, very small. The mass of a single fluorine atom is less than one-trillionth of a billionth of a gram! The mass of 1 atom of H weighs approximately 1.67 x 10 -27 kg.

44. Atomic mass units… or amu’s for short. It is the unit of the mass of the elements found on the periodic table.

45. Scientists like a standard… One amu is equal to 1/12 the mass of carbon- 12. Think about it: 6 p+ and 6 n 0 = 12. Carbon-12 Chemists use this standard to compare units of atomic mass. It’s a relative scale… relative to C- 12. 45

46. Average atomic mass This is the number you see on the periodic table. 46

47. Average Atomic Mass When we talk about atomic mass, we mean the mass of one atom of an element. When we talk about an element as a whole, we have to take into consideration the masses of ALL of its isotopes.

48. How do we do that?? The average atomic mass which is listed on the periodic table takes into consideration all of its isotopes. But some isotopes are more abundant than others… So this average is weighted by natural abundance.

49. Which isotope of Cl is more abundant?

50. Right! So to give chlorine-35 its due, it has more “weight” in the average than the other isotope. Chlorine-35 makes a greater contribution to chlorine’s overall average. It’s like how your grades are averaged…

51. Average atomic mass… Elements rarely occur as only one isotope. They exist as mixtures of different isotopes of various masses. This way, the less common isotopes are accounted for. 51

52. Don’t confuse mass number with average atomic mass. Mass number is the mass of one particular atom. Average atomic mass is the average mass of a group of atoms of the same element that takes into consideration all the isotopes. 52

53. Next up… 53

54. Yes, that little guy is very cute, but in the world of chemistry, a mole is very useful for counting very, very small things. Like atoms!

55. Dozen = 12 Pair = 2 The Mole (mol): A unit to count numbers of particles Ream of paper Baker’s dozen GrossFortnightGoogol Donkey power

56. 1 Mole = 6.022 x 10 23 Dozen = 12 Pair = 2 The Mole (mol): A unit to count numbers of particles Ream of paper Baker’s dozen GrossFortnightGoogol Donkey power

57. 1 mole = 602,213,670,000,000,000,000,000 particles By definition, a mole is a counting unit for very large numbers! Ok… so what’s the good of it??

58. The answer is that moles give us a consistent method to convert between atoms/molecules and grams. It's simply a convenient unit to use when performing calculations. 58

59. Micro World atoms and molecules Macro World grams

60. Avogadro’s Number…

61. A mole of carbon atoms is 6.022x10 23 carbon atoms. A mole of students is 6.022x10 23 students. 1 mole of anything = 6.022x10 23 of that thing. 61

62. 62 It's a lot easier to write the word 'mole' than to write '6.022x10 23 ’ anytime you want to refer to a large number of things! Basically, that's why this particular unit was invented.

63. 1 mole of M&Ms… 63

64. 7 x 10 22 stars in our universe (visible)

65. In every day life Moles as a counting unit is not really practical. But to relate the number of atoms to the mass in grams of an element or compound is very, very practical! And handy…

66. The abbreviation for mole is mol. Molar mass is the weight of one mole of a chemical compound or element. Molar mass is usually written in units g/mol. 66

67. Moles and grams are related 1 mole of carbon-12 atoms has a mass of 12.00 g. The molar mass of C-12 is 12.00 g/mol. For any element, its mass in amu = its molar mass (in g/mol)

68. The link to the periodic table Since 1 mole of an element contains several isotopes, an element’s molar mass in g/mol equals its average atomic mass from the periodic table (which is in amu’s).

69. 2.00 mol He x 4.00 g He = 8.00 g He 1 mol He We can convert between moles and grams… and like it! The molar mass of He is 4.00 g/mol. To find how many grams are in 2.00 mol of He:

70. Let’s try some more… Textbook pg. 126 Practice 1. a, b, c, d. Then pg. 127 Math skills: 13, 14

71. Compounds also have molar mass Compounds are made up of atoms joined together in specific ratios. To find the molar mass of a compound, you can add up the molar masses of all the atoms in a molecule of that compound.

72. H 2 0 for example… H x 2 = 1.01 g/mol x 2 = O = 16.00 g/mol The sum is 18.02 g/mol What does this value tell you?

73. Ok… I’ll tell you! Molar mass = the mass in grams of 1 mol of a substance. The mass of 1 mol of water is 18.02 g. The total mass of 6.022 x 10 23 water molecules = 18.02 g.

74. Let’s try this with carbon monoxide.

75. What is the molar mass of CO?

77. 12.01 + 16.00 = 28.01 g/mol

78. Target Qs 1)How many moles are in 5.2 x 10 6 g of F? 2)Calculate the number of moles in 4.9 x 10 -5 g of Xe. 3)Calculate the number of moles in 8.43 x 10 3 g of Al.

79. Be able to answer these questions at the end of this section: 1. What is the difference between protons, neutrons and electrons? 2. What do atoms of an element have in common with other atoms of the same element? 3. What unit is used to express atomic mass?

80. What’s the difference between mass number and the average atomic mass on the periodic table?