Atoms Molecules Ions Isotopes and Abundance and the
Atoms, Molecules & Ions Isotopes and % Abundance. . and the historical development of the human understanding of matter, atoms, and subatomic particles. Bonus points may be available for suggesting good wrong answers for future use. So if you were thinking that the answer you really wanted wasn’t among the choices, let me know.
A compound made of carbon and oxygen was analyzed and the follow data was obtained. Which law do these data illustrate? 1. 2. 3. 4. mass of C (g) mass of O(g) 12 2. 5 0. 625 1 The law of conservation of matter The law of multiple proportions The law of constant composition The law of conservation of mass 16 3. 2 0. 80 1. 33 2
A compound made of carbon and oxygen was analyzed and the follow Data was obtained. Which law do these data illustrate? mass of C (g) mass of O(g) 12 2. 5 0. 625 1 16 3. 2 0. 80 1. 33 1. The law of conservation of matter 2. The law of multiple proportions 3. The law of constant composition • aka law of definite proportions 4. The law of conservation of mass 3
One compound of carbon and oxygen contains 1. 333 g of oxygen per gram of carbon, whereas a second compound contains 2. 666 g of oxygen per gram of carbon. What chemical law do these data illustrate? 1. 2. 3. 4. The law of conservation of matter The law of multiple proportions The law of constant composition The law of conservation of mass 4
One compound of carbon and oxygen contains 1. 333 g of oxygen per gram of carbon, whereas a second compound contains 2. 666 g of oxygen per gram of carbon. What chemical law do these data illustrate? 1. The law of conservation of matter 2. The law of multiple proportions • this law can be demonstrated with molecular compounds and transition metal compounds because of the many oxidation state possibilities • CO and CO 2 • Fe 2 O 3 and Fe. O 3. The law of constant composition 1. The law of conservation of grams 5
One compound of carbon and oxygen contains 1. 333 g of oxygen per gram of carbon, whereas a second compound contains 2. 666 g of oxygen per gram of carbon. If the first compound has an equal number of oxygen and carbon atoms, what can we conclude about the composition of the second compound? 1. 2. 3. 4. The second compound must have twice as many oxygen atoms per carbon atom. The second compound must have half as many oxygen atoms per carbon atom as the first compound. The second compound contains half as many carbon atoms as the first compound. The first compound contains half as many carbon atoms as the second compound. 6
One compound of carbon and oxygen contains 1. 333 g of oxygen per gram of carbon, whereas a second compound contains 2. 666 g of oxygen per gram of carbon. If the first compound has an equal number of oxygen and carbon atoms, what can we conclude about the composition of the second compound? 1. 2. 3. 4. The second compound must have twice as many oxygen atoms per carbon atom. The second compound must have half as many oxygen atoms per carbon atom as the first compound. The second compound contains half as many carbon atoms as the first compound. The first compound contains half as many carbon atoms as the second compound. 7
What happens to most of the α particles that strike the gold foil in Rutherford’s experiment, and why do they behave that way? 1. α particles are scattered across a range of deflection angles due to the high density of the foil nuclei. 2. Most α particles pass through the foil without being deflected because most of the volume of the atoms that comprise the foil is empty space. 3. Most α are scattered at acute angles as they pass close to the foil nuclei. 4. Most α particles are deflected in a backwards direction from the foil due to the high density of the foil atom nuclei. 8
What happens to most of the α particles that strike the gold foil in Rutherford’s experiment, and why do they behave that way? 1. α particles are scattered across a range of deflection angles due to the high density of the foil nuclei. 2. Most α particles pass through the foil without being deflected because most of the volume of the atoms that comprise the foil is empty space. 3. Most α are scattered at acute angles as they pass close to the foil nuclei. 4. Most α particles are deflected in a backwards direction from the foil due to the high density of the foil atom nuclei. 9
Radioactive substances emit “rays. ” These rays are particles or energy. In the image below, which ray represents beta particles? 1. 2. 3. 4. orange red green any color could represent a beta particles, since we don’t know if the charge of the plates are the same magnitude. 10
Radioactive substances emit “rays. ” These rays are particles or energy. In the image below, which ray represents beta particles? 1. orange 2. red 3. green 4. any color could represent a beta particles, since we don’t know if the charge of the plates are the same magnitude. • Let’s assume the plates are the same magnitude of charge, why do the alpha particles deflect less than the beta particles? 11
Radioactive substances emit “rays. ” These rays are particles or energy. In the image below, which ray represents beta particles? • Let’s assume the plates are the same magnitude of charge, why do the alpha particles deflect less than the beta particles? • Beta particles have a 1− charge, and alpha particles have 2+ charge, thus one might think alpha might deflect more, however, the mass of alpha particle is ~8000 times more massive and thus does not bend as much. 12
Emissions from Radioactive Substances • • • Alpha particles, essentially a helium nucleus ✓ made of 2 protons & 2 neutrons, +2 charge ✓ represented as or ✓ fairly heavy, slower moving ✓ clothing is enough to stop their progress Beta particles are essentially electrons ✓ represented as or ✓ very little mass, fast moving ✓ requires a thin metal foil to stop their progress Gamma rays is essentially energy ✓ represented as ✓ more energetic than x-rays ✓ requires thick lead shield to stop their progress 13
How many nucleons are there in a 14 nuclide (aka isotope) of C? 1. 2. 3. 4. 6 8 12 14 14
How many nucleons are there in a 14 nuclide (aka isotope) of C (carbon-14)? a. b. c. d. • • 6 14 8 12 14 Nucleons are protons and neutrons Remember the mass number minus the atomic number (14 - 6 = 8) always equals the number of neutrons. Mass 15
How many electrons would an isotope 3+ of Cr ion contain? 1. 2. 3. 4. 5. 3 21 24 28 not enough information to determine 16
How many electrons would an isotope 3+ of Cr ion contain? 1. 2. 3. 4. 5. 3 21 24+ 24 Cr 28 not enough information to determine 24 e- 21 e 24+ loses three electrons Cr 3+ 17
A particular atom of chromium has a mass of 52. 94 amu, whereas the atomic weight of chromium is 51. 99 amu. Explain the difference in the two masses. 1. The 52. 94 amu value and the 51. 99 amu value represent two different isotopes of chromium. 2. The atomic weight of chromium is less than the mass of the specific chromium atom since atomic weights are used to describe neutral atoms. 3. The atomic weight of chromium (51. 99 amu) is an average atomic mass of all the naturally occurring isotopes of chromium, whereas the 52. 94 is the mass of just one of those isotopes. 18
A particular atom of chromium has a mass of 52. 94 amu, whereas the atomic weight of chromium is 51. 99 amu. Explain the difference in the two masses. 1. The 52. 94 amu value and the 51. 99 amu value represent two different isotopes of chromium. 2. The atomic weight of chromium is less than the mass of the specific chromium atom since atomic weights are used to describe neutral atoms. 3. The atomic weight of chromium (51. 99 amu) is an average atomic mass of all the naturally occurring isotopes of chromium, whereas the 52. 94 is the mass of just one of those isotopes. 19
Both chlorine and bromine exist as two naturallyoccurring isotopes, distributed as shown to the right. % natural occurrence is based on the distribution of isotopes. Chlorine reacts with bromine to form Cl. Br. How many different possible molar masses are there for Cl. Br? No Calculator isotope % natural occurrence chlorine-35 76% chlorine-37 24% bromine-79 51% bromine-81 49% 20
Both chlorine and bromine exist as two naturallyoccurring isotopes, distributed as shown to the right. % natural occurrence is based on the distribution of isotopes. Chlorine reacts with bromine to form Cl. Br. How many different possible molar masses are there for % natural Cl. Br? isotope occurrence Three possible molar masses: • • • chlorine-35 76% 35+79=114 chlorine-37 35+81=116, (37+79=116, repeat) bromine-79 bromine-81 37+81=118 24% 51% 49% 21
Both chlorine and bromine exist as two % natural isotope occurrence naturally-occurring isotopes, distributed as shown to the right. % natural occurrence is chlorine-35 76% based on the distribution of isotopes. chlorine-37 24% Chlorine reacts with bromine to form Cl. Br. Given the three possible molar masses: 114, 116, 118, select the choice from the right for the approximate fractional distribution in natural occurring compounds of these three molar masses? No Calculator bromine-79 bromine-81 51% 49% Molar Masses 114 116 118 1 2 3 4 5 ¼ ⅓ ⅜ ½ ½ ½ ⅓ ½ ¼ ⅜ ¼ ⅓ ⅛ ¼ ⅛ 22
Both chlorine and bromine exist as two naturally-occurring isotopes, distributed as shown to the right. % natural occurrence is based on the distribution of isotopes. Chlorine reacts with bromine to form Cl. Br. Given the three possible molar masses: 114, 116, 118, select the choice from the right for the approximate fractional distribution in natural occurring compounds of these three molar masses? Consider the % occurrence of each isotope to be ¼, ¾, ½. To get frequency of molecule, multiply the two frequencies of the isotopes together. From previous problem: the three possible molar masses: • • • 35+79=114 ¾*½=⅜ 35+81=116 ¾*½=⅜ 35+79=116 ¼*½=⅛ } ½ No Calculator isotope % natural occurrence chlorine-35 chlorine-37 bromine-79 bromine-81 76% 24% 51% 49% Molar Masses 114 116 118 1 2 3 4 5 ¼ ⅓ ⅜ ½ ½ ½ ⅓ ½ ¼ ⅜ ¼ ⅓ ⅛ ¼ ⅛ 23
isotope % abundance mass The element X has 48 three naturally X 25 47. 98 50 X occurring isotopes. 50 49. 96 52 X 25 51. 99 The isotopic masses and % abundance are given in the table to a. 48 the right. Estimate the b. 49 value that the average c. 50 atomic mass of the d. 51 element would be closest to. No Calculator e. 52 24
The element X has three isotope % abundance mass 48 naturally occurring X 25 47. 98 isotopes. The isotopic 50 X 50 49. 96 masses and % abundance 52 X 25 51. 99 are given in the table to 1. 48 the right. Calculate the 2. 49 value that the average 3. 50 atomic mass of the 4. 51 element would be closest 5. 52 to. No calculator necessary. Look at the %abundance to realize that an equal % of 52 and an equal % of 48 would make the average fall exactly in the middle at mass 50 25
Chlorine has two isotopes, 35 Cl (75. 78% 37 abundant) and Cl (24. 22% abundant). How many different molar masses are possible for a Cl 2 molecule? 1. 2. 3. 4. 5. 6. 1 2 3 4 5 Not enough information to determine Graphical Readout from a Mass Spectrometer 26
Chlorine has two isotopes, 35 Cl (75. 78% 37 abundant) and Cl (24. 22% abundant). How many different molar masses are possible for a Cl 2 molecule? 1. 1 2. 2 3. 3 • 35+35, 35+37, 37+37 • the percentages in this problem are distractors 4. 4 5. 5 Graphical Readout from a Mass Spectrometer 6. Not enough information to 27 determine
Mass Spectrometry; Determining masses and percentages of isotopes. Mass Spectrometer Percent Abundance determined from signal intensity Graphical Readout from a Mass Spectrometer 28
A sample of zinc was run through a mass spectrometer. Which of the following statements can be concluded from the spectrograph shown below. Signal Intensity 1. Zn has 5 oxidation states. 2. Zinc does not have an isotope with 35 neutrons. 3. There are 4 naturally occurring isotopes. 4. The most common 65 isotope is Zn. 29
Chlorine has two isotopes, 35 Cl (75. 78% abundant) and 37 Cl (24. 22% abundant). How many different molar masses are possible for a Cl 2 molecule? Given the three possible molar masses: 70, 72, 74, select the choice from the right for the approximate fractional distribution in natural occurring elemental molecules of these three molar masses? 1. 2. 3. 4. 5. 6. 1 2 3 4 5 Not enough information to determine Molar Masses 1 2 3 4 5 6 70 72 74 ⅜ ⁹/₁₆ ¾ ⁹/₁₆ ¼ ¾ ⅜ ³/₁₆ ¼ ⅜ ½ ½ ¼ ⅟₁₆ 30
Chlorine has two isotopes, 35 Cl (75. 78% abundant) and 37 Cl (24. 22% abundant). How many different molar masses are possible for a Cl 2 molecule? Given the three possible molar masses: 70, 72, 74, select the choice from the right for the approximate fractional distribution in natural occurring elemental molecules of these three molar masses? 1. 2. 3. 4. 1 2 3 4 • • 1. 1 35 + 35 ¾ * ¾ = 9/₁₆ 35 + 37 and 37 + 35 • • Molar Masses ¾*¼=³/₁₆ + ¼*¾=³/₁₆ = ⅜ 37 + 37 ¼ * ¼ = ⅟₁₆ 5 Not enough information to determine 2 3 4 5 6 70 72 74 ⅜ ⁹/₁₆ ¾ ⁹/₁₆ ¼ ¾ ⅜ ³/₁₆ ¼ ⅜ ½ ½ ¼ ⅟₁₆ 31
- Slides: 31