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Prentice Hall Chemistry (c) 2005

Prentice Hall Chemistry (c) 2005. Power Point created by Daniel R. Barnes on or before 10/13/2010 w/possible subsequent edits. Section Assessment Answers Chapter 4. Let's Play with Blocks!.

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Prentice Hall Chemistry (c) 2005

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  1. Prentice Hall Chemistry(c) 2005 Power Point created by Daniel R. Barnes on or before 10/13/2010 w/possible subsequent edits. Section Assessment Answers Chapter 4 Let's Play with Blocks! WARNING: some images and content in this presentation may have been taken without permission from the world wide web. It is intended for use only by Mr. Barnes and his students. It is not meant to be copied or distributed.

  2. Click the frog if you want to jump to a particular section. Click anywhere else if you want to start from the beginning and walk through all of the answers.

  3. 1. [See textbook for question.] Democritus believed that atoms were indivisible (you couldn’t split them into pieces, hence the name “atomos”), and they were indestructible. Democritus 460 B.C. – 370 B.C. Do we still believe these things to be true? 4.1 Section Assessment No. Atoms can be split. J. J. Thomson discovered the electron in c. 1897. The “atom bomb” gets its explosive power from splitting uranium or plutonium atoms in half.

  4. 1. [See textbook for question.] Democritus believed that atoms were indivisible (you couldn’t split them into pieces, hence the name “atomos”), and they were indestructible. Democritus 460 B.C. – 370 B.C. Do we still believe these things to be true? No. Atoms can be destroyed. 4.1 Section Assessment Antimatter, discovered in 1932 by Carl D. Anderson, destroys matter when it touches it. Matter and antimatter explode with a hundred times more force than nuclear bombs as they annihilate each other.

  5. 2. [See textbook for question.] Dalton used experimental methods, whereas Democritus had used only imagination and reasoning. Dalton also had much better knowledge of the elements, and he studied the mass ratios in which elements combined to make compounds. Some of Dalton’s elements 4.1 Section Assessment Modern “States of Matter” John Dalton 1766-1844 Ancient Greek “elements” Democritus 460 B.C. – 370 B.C. hot gas or plasma hydrogen oxygen nitrogen carbon sulfur phosphorus fire air gas water liquid earth solid

  6. 3. [See textbook for question.] The scanning tunneling microscope can generate pictures where individual atoms can be distinguished. For instance, on page . . . 103, each iron atom in the picture appears as a single . . . cone. 4.1 Section Assessment

  7. Scanning Tunneling Microscope

  8. 1981

  9. 4. [See textbook for question.] i) All matter is composed of tiny, indivisible particles called “atoms”. Is everything he said here still believed to be true? ii) Atoms of the same element are identical. The atoms of any one element are different from those of another element. Is everything he said here still believed to be true? 4.1 Section Assessment iii) Atoms of different elements can physically mix together or can chemically combine in simple whole-number ratios to form compounds. Is everything he said here still believed to be true? iv) Chemical reactions occur when atoms are separated, joined, or rearranged. Atoms of one element, however, are never changed into atoms of another element as a result of chemical reaction. Is everything he said here still believed to be true?

  10. 5. [See textbook for question.] According to Dalton, atoms can not be changed from one element to another. For example, a carbon atom will always be a carbon atom, forever. Of course, we know better than that now. We now know that in addition to chemical reactions, which merely rearrange atoms, there are also nuclear reactions, which DO change atoms from one element to another. 4.1 Section Assessment For instance, carbon-14 atoms will spontaneously turn into nitrogen-14 atoms by the process of radioactive decay. Does that mean that Dalton was an idiot? NO WAY! Dalton was brilliant. Even Einstein was wrong about certain things.

  11. 6. [See textbook for question.] 5 x 10-2 nm to 2 x 10-1 nm That’s the short version of the answer. If you know how to get that answer, then click the red button below to skip to #7. You can also click the red button if you just don’t care about #6. If you don’t understand how to get the answer to #6 and you do want to learn how, then click the green button instead. 4.1 Section Assessment I want to learn about #6! Skip to #7

  12. Okay. Buckle your seatbelt.

  13. 6. [See textbook for question.] The book says, on page 103, at the beginning of the 3rd paragraph, that “The radii of most atoms fall within the range of 5 x 10-11 m to 2 x 10-10 m.” First of all, we’d better make sure we know what “radii” means. The width of a circle is called its “diameter”. 4.1 Section Assessment Half the width of a circle is called its “radius”. DIAMETER The radius is the distance from the center of the circle to the edge of the circle. radius “Radii” is just the plural of “radius”.

  14. And now, for some stuff that you would already know if I had made you learn chapter three . . .

  15. A yardstick is three feet long. An American football field is 100 yards long. These days, America is the only country that measures distance in yards. The rest of the world uses the metric system. In the metric system, the meter is used instead of the yard. A meter is a little bit longer than a yard.

  16. An ordinary ruler is twelve inches long. If you flip it around . . . . . . You will notice that it is about 30 centimeters long. A paperclip is about one centimeter wide.

  17. If you look closely, you will notice that there are ten tiny marks between each centimeter. These marks are one millimeter apart.

  18. If you look closely, you will notice that there are ten tiny marks between each centimeter. These marks are one millimeter apart.

  19. The wire that a paperclip is made out of is about one millimeter thick. A millimeter is pretty small, isn’t it? A one-millimeter metal wire is still much thicker than a human hair, though.

  20. According to the tables on page 74, how big is a nanometer? It says that 1 m = 109 nm 109 is 1,000,000,000, which is one billion. Therefore, a nanometer is one one-billionth of a meter. The tables also say that 1 m = 103 mm 103 is 1,000, which is one thousand. Therefore, a millimeter is one one-thousandth of a meter. If 1m = 109 nm and 1 m = 103 mm, then . . . 109 nm = 103 mm 10(9-3) nm = 1 mm 106 nm = 1 mm 103 103 1 mm = 1,000,000 nm A nanometer is one one-millionth of a millimeter. That’s small.

  21. If you got confused during the math on that last slide, don’t worry. I was just tyring to show you how ridiculously small a nanometer (nm) is.

  22. REVIEW QUESTIONS What metric unit of length is just a bit longer than three feet? 1 meter = 1 m How wide is a paper clip? 1 centimeter = 1 cm How thick is the wire that a paper clip is made of? 1 millimeter = 1 mm 1 nm = one one-billionth of a meter How big is a nanometer? 1 nm = one one-millionth of a millimeter

  23. GREAT! Now that you know your units, let’s do the math . . .

  24. 6. [See textbook for question.] The book says, on page 103, at the beginning of the 3rd paragraph, that “The radii of most atoms fall within the range of 5 x 10-11 m to 2 x 10-10 m.” Unfortunately, we need to give our answer in nm, not m. Page 103 gives us good information, but it’s in the wrong UNITS. 4.1 Section Assessment We need to CONVERT meters (m) into nanometers (nm). We need to do a UNIT CONVERSION.

  25. 6. [See textbook for question.] nm 5 x 10-11 m 109 5 x 10(-11 + 9) nm x = 1 m 1 5 x 10(-2) nm = If the math here is too scary, don’t freak out. You don’t really need to be able to do this kind of problem right now in chapter 4. Consider this problem extra credit. nm 2 x 10-10 m 109 2 x 10(-10 + 9) nm x = 1 m 1 4.1 Section Assessment 2 x 10(-1) nm = 5 x 10-2 nm to 2 x 10-1 nm

  26. ) • [See textbook for question.] So what the heck do you do with these numbers? 63.5 g = 10.5 x 10-23 g/atom 6.02 x 1023 atoms = 1.05 x 10-22 g/atom 4.1 Section Assessment 10.54817276 6.02 63.5 If the math on this problem was too hard, don’t worry about this one either. It’s kind of like #6. Consider this problem extra credit also.

  27. 8. [See textbook for question.] The three kinds of subatomic particles are the electron, the proton, and the neutron. All atoms are made merely of different combinations of these three fundamental building blocks. Since you are made of atoms, that means that you are made of 4.2 Section Assessment protons, neutrons, and electrons.

  28. 9. [See textbook for question.] From his experiments, Rutherford concluded that an atom is made of a positively-charged nucleus surrounded by a region of empty space in which electrons orbit that nucleus. Rutherford believed that an atom’s nucleus was very tiny compared to the atom as a whole, and that, in spite of this, the nucleus is where most of the atom’s mass is. 4.2 Section Assessment Thus, according to Rutherford’s interpretation of his experimental results, atoms are made mostly of empty space. This implies that all things made of matter, anything that is solid, liquid, or gas, is actually made mostly of empty space.

  29. 10. [See textbook for question.] (Table 4.1 at the top of page 106 summarizes this nicely for you.) Particle Symbol Charge Relative mass 4.2 Section Assessment electron e- 1- 1/1840 proton p+ (or H+!) 1+ 1 neutron n0 0 1 (actually a little more than that)

  30. 11. [See textbook for question.] Thomson, through his cathode ray tube experiments, discovered the electron. Millikan, through his oil drop experiments, determined the charge and mass of the electron. 4.2 Section Assessment

  31. 12. [See textbook for question.] Rutherford expected that the alpha particles he shot at the gold foil would pass through it with little deflection. Instead, he found that, although most did shoot straight through with little or no deflection, some alpha particles were deflected at very large angles, and some alpha particles even bounced back toward the alpha particle source. 4.2 Section Assessment He likened this to shooting a cannonball at a piece of facial tissue and having it bounce back. Rutherford had no idea that there was anything dense and heavy enough in an atom to bounce an alpha particle back to where it came from.

  32. 13. [See textbook for question.] The great majority of the alpha particles went straight through the gold foil, as though nothing were there. 4.2 Section Assessment

  33. 14. [See textbook for question.] Thomson thought the atom was a mass of positive charge with negative electrons embedded in its outer surface. Rutherford’s model didn’t envision the atom being a big ball of positive charge, but, rather, a tiny speck of positive charge in the middle of an almost perfectly empty region of space. 4.2 Section Assessment Rutherford did not envision electrons as stuck in anything, but, rather, as whizzing through space, in “orbit” around the positive nucleus. He envisioned the atom as a tiny solar system, in which the nucleus was like the sun and the electrons were like planets.

  34. #’s 15 – 24 are “Practice Problems”, so the answers are in the back of the book. Look on page R84.

  35. If you still don’t understand how you’re supposed to figure out the answers, ask Mr. Barnes to explain.

  36. 25. [See textbook for question.] The number of protons in an atom determines what element it belongs to. Number of protons is called “atomic number”. 4.3 Section Assessment For instance, all gold atoms have exactly 79 protons in them. Any atom that has 26 protons in it is, by definition, an iron atom.

  37. 26. [See textbook for question.] number of neutrons = mass number – atomic number This is true because mass number = number of protons + number of neutrons . . . 4.3 Section Assessment and atomic number = number of protons

  38. 27. [See textbook for question.] Isotopes of a given element vary only in the number of neutrons in each atom. For instance, most carbon atoms are from the isotope carbon-12, but a few are from the isotope carbon-14. 4.3 Section Assessment Carbon-12 atoms and carbon-14 atoms all have 6 protons, but carbon-12 atoms have only 6 neutrons each, whereas carbon-14 atoms have 8 neutrons each. Incidentally, the two extra neutrons in carbon-14 make that isotope radioactive . . . But we’ll discuss radioactivity later . . .

  39. 28. [See textbook for question.] Atomic mass is calculated by what is called a “weighted average” method (no pun intended). The mass of each known isotope of the element is multiplied by the % abundance of that element. 4.3 Section Assessment Because of this, rare isotopes tend to have a very small effect upon the average atomic mass of an element. Also, the average atomic mass of the element tends to be very close to the atomic mass of the most common isotope of that element.

  40. 29. [See textbook for question.] By looking at the periodic table, one can predict the chemical and physical properties of an element by its location on the table. Here are a few examples of this: *Elements in the same vertical column tend to have the same number of “valence electrons”, and, therefore, similar bonding properties. 4.3 Section Assessment *Elements to the left of the “staircase” are almost all metals, elements to the right almost all nonmetals, and elements touching the staircase mostly metalloids. *Elements with high electronegativies and ionization energies tend to be clustered in the upper right hand corner of the periodic table. [Don’t burden your brain too much with these examples just yet. We’ll be looking at them more closely in chapter 6.]

  41. 30. [See textbook for question.] A platinum-194 atom has a total of 194 protons and neutrons, combined, in its nucleus. (194 is the “mass number” of platinum-194.) Since all platinum atoms have 78 protons, then the symbol for a platinum-194 atoms would be . . . 4.3 Section Assessment Pt 194 78

  42. 31. [See textbook for question.] The average atomic mass of an element is typically not a whole number precisely because it is an average atomic mass. Averages tend to have decimal fractions hanging of the ends of them. An average atomic mass is the weighted average of the atomic masses of all the naturally-occurring isotopes of the element. Even if the atomic masses of the isotopes were whole numbers (which they aren’t), the weighted average of those atomic masses would almost certainly never be a whole number. 4.3 Section Assessment [Don’t worry about this question too much. If you get it, great. If you don’t, no biggie. There are more important concepts for you to master in this class than this one.]

  43. 32. [See textbook for question.] If an atom does have an electric charge, then it will be written where the flashing blue squares are. a. Li Li 6 7 3 3 (Lithium’s atomic number is 3.) Protons: 3 3 (# of neutrons = mass number – atomic number) 4.3 Section Assessment Neutrons: 3 4 (no electrical charge listed, so # of electrons = # of protons = atomic number) Electrons: 3 3

  44. 32. [See textbook for question.] b. Ca Ca 42 44 20 20 Protons: 20 20 4.3 Section Assessment Neutrons: 22 24 Electrons: 20 20

  45. 32. [See textbook for question.] c. Se Se 78 80 34 34 Protons: 34 34 4.3 Section Assessment Neutrons: 44 46 Electrons: 34 34

  46. 33. [See textbook for question.] Sr (strontium) Be (beryllium) Mg (magnesium) Ba (barium) Ra (radium) If two elements are in the same vertical column of the periodic table, they probably have similar properties. 4.3 Section Assessment Because of this, columns are also known as “families”. The above-named elements comprise the family known as the . . . “alkaline earth metals”.

  47. The End Yay for atoms!

  48. Jump to 4.1 Section Assessment Jump to 4.2 Section Assessment Press your “End” button at any time to jump to this page. Jump to 4.3 Section Assessment

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