Slide 1 / 104 Slide 2 / 104 New Jersey Center for Teaching and Learning Progressive Science Initiative AP Chemistry This material is made freely available at www.njctl.org and is intended for the non-commercial use of students and teachers. These materials may not be used for any commercial purpose without the written permission of the owners. NJCTL maintains its Summer Assignment website for the convenience of teachers who wish to make their work available to other teachers, "The Basics" participate in a virtual professional learning community, and/or provide access to course materials to parents, students and others. Click to go to website: www.njctl.org www.njctl.org Slide 3 / 104 Slide 4 / 104 1 Which of the following were a part of Dalton's Atomic Dalton's Atomic Theory Theory? By the late 1800's, scientists worldwide had adopted John Dalton's Atomic Theory as the best explanation for the behavior of matter. A All matter is composed of atoms Matter is composed of atoms, B Atoms get rearranged in chemical reactions which are indivisible. Each compound consists of a set ratio of atoms. C Atoms of the same element are identical Atoms of same element are C C C C D A and B identical E A, B, and C Atoms of different elements are Si C different Atoms are not changed, created, Cl Cl H H or destroyed in a reaction, they H Cl are simply rearranged Cl H Slide 5 / 104 Slide 6 / 104 2 Which of the following components of Dalton's Protons, neutrons, and electrons theory was proved incorrect by the discovery of isotopes? A All matter is composed of atoms Atoms are composed of subatomic particles. B Atoms are rearranged in chemical reactions C Atoms of the same element are identical D Both A and B Protons and neutrons have similar masses (roughly 1 amu) and together constitute the mass number (A) of an atom. E A, B, and C # of protons + # of neutrons = mass number (A)
Slide 7 / 104 Slide 8 / 104 Protons, neutrons, and electrons Protons, neutrons, and electrons Each element consists of atoms which differ in the number of protons compared to atoms of different elements. The atomic If an atom is electrically neutral, the number of electrons and number (Z) is equal to the number of protons in an atom. protons will be the same. # of protons = # of electrons # of protons = atomic number (Z) (neutral atom) Slide 9 / 104 Slide 10 / 104 Nuclide Symbols Nuclide Symbols & protons and neutrons There are two common ways the atomic mass and number are The number of protons and neutrons can be easily determined indicated for an atom. from the nuclear symbol. Method 1: Provides all information Example: How many protons and neutrons are present in the A < --- mass number 119 3 following? Symbol Cs or H 220 88 protons Z < --- atomic number 55 1 a) Ra 220 - 88 = 132 neutrons move for answer 88 Method 2: Must look up atomic number on the periodic table. Symbol - mass number Cs-199 or H-3 b) Au - 197 79 protons (from PT) 6 atomic number move for answer C 197 - 79 = 118 neutrons 12.01 Slide 11 / 104 Slide 12 / 104 3 Barium is used to help take X-rays of the digestive 4 Which is the correct number of protons in an atom of system of the human body. What is the atomic vanadium (V)? number of barium (Ba)? A 38 A 23 B 48 B 51 C 137 C 18 D 4 D 24 E 56 E 50
Slide 13 / 104 Slide 14 / 104 6 How many neutrons are present in an oxygen 5 What is the mass of an element that has 10 protons atom with a mass of 18 amu? and 11 neutrons? Slide 15 / 104 Slide 16 / 104 7 What is the mass of an element with 18 protons, 18 8 How many neutrons are present in atom with a mass of electrons, and 22 neutrons? 13 amu and an atomic number of 7? Slide 17 / 104 Slide 18 / 104 9 How many neutrons are present in a neutral atom 10 How many electrons does this neutral element of Sr-80? have? A 38 B 32 C 38 D 80 Na 23 E 42 11 Sodium Atom
Slide 19 / 104 Slide 20 / 104 11 How many neutrons does this element have? 12 Which of the following has 45 neutrons? A 80 Kr B 80 Br C 78 Se Na 23 D 103 Rh 11 Sodium Atom Slide 21 / 104 Slide 22 / 104 Isotopes and a hole in Dalton's Theory Average Atomic Mass Dalton postulated that all atoms of a given element were identical. In the early 1900's scientists determined that certain atoms of lead When one examines even the smallest sample of an element, there were more stable than others - so there must be a difference! are hordes of atoms present. All of the stable isotopes of that element The difference was in the mass of the different atoms of lead. Since will be in the sample but not in the same abundance. the atoms were all lead they must have the same atomic number or number of protons. The difference in mass must be due to differing numbers of neutrons amongst the lead atoms!! For example, in a sample of carbon atoms, roughly 99% of the Atoms of the same element with differing numbers of neutrons atoms will be C-12 while 1% will be C-13. These percentages do are called isotopes! not vary no matter where, when, or how the sample was taken. Pb - 204 Pb - 206 82 protons 82 122 neutrons 124 Slide 23 / 104 Slide 24 / 104 Average Atomic Mass Calculating an Average Atomic Mass To find the average atomic mass of an element simply find the sum of the contribution of each isotope by multiplying the mass of each The mass listed on the isotope by it's abundance (expressed as a decimal instead of a %) 6 periodic table is a and adding them all together. C weighted average of the average atomic 12.01 isotopes of that particular mass element. Example: Neon consists of three stable isotopes: Ne-20, Ne-21, and Ne-22. If the relative abundance of these are 90.48%, 0.27%, and 9.25% respectively, what is the atomic mass of neon? *Note: The average atomic mass of carbon is much closer to 12 compared to 13. This is due to the much larger abundance of C-12. 20(.9048) + 21(0.0027) + 22(0.0925) = 20.18 amu
Slide 25 / 104 Slide 26 / 104 13 Which pair of atoms constitutes a pair of Calculating % Abundances from an isotopes of the same element? Average Atomic Mass If the average atomic mass is known, the % abundance of each 14 14 X A 6 X isotope can be determined if the mass of each isotope is known. 7 Example: There are two stable isotopes of calcium: Ca -40 (39.96) and B 14 X 12 X Ca -46 (45.95). Using the average atomic mass of calcium from the 6 6 periodic table, calculate the % abundance of each isotope of calcium. C 17 X 17 Step 1: Set the abundance of each isotope as equal to "x" and "y" X 9 8 Both decimal abundances must add up to 1. D x + y = 1 so y = 1-x 19 X 19 X 10 9 Step 2: Solve for x using average atomic mass equation. E 20 X 21 39.96(x) + 45.95(1-x) = 40.08 (from PT) X 11 10 -5.99x = -5.87 --> x = 0.98 or 98% 98% Ca-40 and 2% Ca-46 Slide 27 / 104 Slide 28 / 104 14 Which of the following is TRUE of isotopes of an 15 An atom that is an isotope of potassium (K) element? must... They have the same number of protons A Have 20 protons A The have the same number of neutrons B Have 19 neutrons B They have the same mass C Have 19 protons C D They have the same atomic number A mass of 39 D A and D E A total of 39 protons and neutrons E Slide 29 / 104 Slide 30 / 104 16 Which species is an isotope of 39 Cl? 17 Calculate the atomic mass of oxygen if it's abundance in nature is: A 40 Ar + B 34 S 2- 99.76% oxygen-16, 0.04% oxygen-17, and C 36 Cl - 0.20% oxygen-18. D 80 Br E 39 Ar (liquid oxygen)
Slide 31 / 104 Slide 32 / 104 18 Sulfur has two stable isotopes: S-32 and S-36. Using 19 Copper has two stable isotopes, Cu-63 (62.93) and Cu-65 (64.93). Using your periodic table, determine the average atomic mass on the periodic table, which the % abundance of each isotope of copper. of the following best approximates the natural relative abundances of these isotopes of sulfur? 50% S-32 and 50% S-34 A 25% S-32 and 75% S-34 B 75% S-32 and 25% S-34 C 95% S-32 and 5% S-34 D E 5% S-32 and 95% S-34 Slide 33 / 104 Slide 34 / 104 Atomic Models Atomic Models The model of the atom has changed significantly over the years. Nuclear Model Due to Rutherford's gold foil scattering experiment, it was determined the protons were clustered together in a highly dense nucleus. It was Plum Pudding Model postulated that the electrons orbited this nucleus. Protons and electrons are spread evenly throughout the atom Volume occupied by Nucleus containing by electrons protons and neutrons - - + + - + - - - + + 10 -4 A o 1-5A o Slide 35 / 104 Slide 36 / 104 Interaction of Light and Matter Interaction of Light and Matter Scientists noticed that atoms absorbed and emitted Scientists noticed that light interacted with matter on the subatomic energy of only certain frequencies thereby creating scale. For example, light of the right frequency could dislodge an absorption and emission spectra. electron from an atom (photoelectric effect) In order to understand atomic structure we must recall the basic emission spectrum properties of a wave - specifically waves of EM radiation. absorption spectrum Properties of a EM wave Relationships between properties Wavelength ( ) c = v and E = h v Frequency (v) c = 3.00 x 10 8 m/s Energy (E) h = 6.626 x 10 -34 J*s Energy and frequency are directly related while wavelength is inversely related to both.
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