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Unformatted text preview: Chapter 2 Chapter Atoms and Elements Dalton’s Atomic Theory Dalton’s (beginning of 19th century) • All matter is composed of tiny, All indivisible particles called atoms • All atoms of a given element are All identical to each other and different from those of other elements from • A chemical reaction merely involves chemical a change in the groupings of atoms and not creation or destruction of atoms (Law of Conservation of Mass) atoms • Compounds consist of atoms of Compounds more than one element combined in particular ratios (Law of Constant Composition and Law of Multiple Proportions) Proportions) Building up Atomic Structure Building • Benjamin Franklin (1706-1790) discovered two Benjamin types of electricity, (+) and (-). • Henri Becquerel discovered radioactivity on 1896. Henri Pierre and Marie Curie continued that work: atoms disintegrate, i.e., they are divisible. divisible • John J. Thomson discovered the electron and John electron determined its charge/mass ratio (1896-97). determined • Robert A. Millikan (1909) determined the charge Robert and mass of electron. and • Ernest Rutherford (1911-19) discovered the Ernest proton. proton • James Chadwick (1932) discovered the neutrons, James neutrons that are with the protons in the nucleus of atoms. nucleus Atomic Structure Atomic • subatomic particles neutron: no charge, 1.0087 amu, n neutron proton: +1 charge, 1.0073 amu, p+ proton electron: –1 charge, 0.0005486 amu, e– electron • n and p+ packed tightly into dense core called nucleus nucleus • e– distributed more diffusely in space surrounding nucleus surrounding e– n p+ e– Actual size: Radius of atom ~ 100 pm (10-10 m) Radius of nucleus ~ 0.001 pm Then, if radius of atom was ~ 100 m (a small football stadium), the radius of the nucleus would be ~ 0.001 m = 1 mm V ∝ r3 Then, Vatom/Vnucleus ≅ 1015. Atom is 1015 times bigger Atomic number and Mass number • all atoms of a given element have the all same number of protons same • number of protons in an atom given by the atomic number, Z atomic • neutral atoms have same number of neutral protons and electrons protons • atoms gain or lose charge by gaining or atoms losing electrons only (not protons) losing • total number of protons and neutrons total given by mass number, A. A = #p+ + #n mass Symbol Symbol mass number charge A X Z atomic number n element symbol Examples Examples Determine the numbers of electrons, Determine protons, and neutrons in each of the following atoms. following 40 Ar 18 40 Ar 18 Z = 18, therefore the atom has 18 p+ 18, A = 40, 40, A = # of p+ + # of neutrons of Therefore, # neutrons = A − # p+ Therefore, 40 – 18 = 22 neutrons 40 Charge, n = 0, therefore # of e– = # p+ = 18 209 2+ Pb Pb 82 • Z = 82, therefore 82 p+ • A = 209, therefore 209 p+ and n total and • # neutrons = A − # p+ = 209 – 82 = 127 n neutrons • n = 2+, 2+, • Therefore # e– = 82 p+ − 2 = 80 e– (lost 2 e–) 31 15 P 3– 31 3– P 15 Z = 15, therefore 15 p+ 15, 31 3– P 15 Z = 15, therefore 15 p+ 15, A = 31, therefore 31 p+ and n total 31 15 P 3– Z = 15, therefore 15 p+ 15, A = 31, therefore 31 p+ and n total 31 – 15 = 16 n 31 3– P 15 Z = 15, therefore 15 p+ 15, A = 31, therefore 31 p+ and n total 31 – 15 = 16 n n = 3 –, (gained 3 e–) − − Isotopes Isotopes • atoms (of same element) that have atoms the same number of protons but different numbers of neutrons, i.e., different A • may or may not have same number may of electrons of 52 24X 55 24X 52 24X 55 24X 52 24X 52 20X 52 X 24 55 52 X 24 52 X 20 X 24 52 3+ 50 24 24 X X Which of the Which pairs of atoms is(are) isotope(s)? isotope(s)? Isotope abundance Isotope A sample of naturally occurring sulfur contains several isotopes with the following abundances Isotope % abundance 32 32S 95.02 33 33S 0.75 32 34 34S S, 33S, 34S, 36S 4.21 16 16 16 16 36 36S 0.02 The %s have been determined experimentally. # of atoms of a given isotope of % Abundance = ─────────────────────────── x 100 Abundance ──────────────────────────── Total # of atoms of all isotopes of element Mass Spectrometry is employed to determine Isotopic Abundances determine • mass spectrometer. – Device generates ions that pass down an Device evacuated path inside a magnet. evacuated – Ions are separated based on their Ions charge/mass ratio. Mass is, then, calculated. charge/mass Atomic Weight Atomic The atomic mass and Isotope Abundances are determined by means of Mass Spectrometry. determined Mass Atomic mass of isotope carbon-12 is defined exactly 12 Atomic amu whereas all others of carbon and other elements amu are referred to that and do not have integer values. % abundance isotope 1 Atomic weight = x (mass isotope 1) 100 100 % abundance isotope 2 + x (mass isotope 2) + … 100 100 Example Example Isotope % abundance mass (amu) 64 Zn 48.6 63.9291 66 Zn 27.9 65.9260 67 Zn 4.1 66.9721 68 Zn 18.8 67.9249 70 Zn 0.6 69.9253 Example, contd. Example, %abund.i %abund. Atomic weight of Zn = ∑ × mi Atomic Zn 100 100 A.W.= 0.486 × 63.9291 + 0.279 × 65.9260 + … A.W.= + 0.041 × 66.9721 + 0.188 × 67.9249 + … 0.041 + 0.006 × 69.9253 = 65.4 amu 0.006 65.4 # 25. Gallium has two naturally occurring isotopes, 69Ga and 71Ga, with masses of 68.9257 amu and 70.9249 amu, respectively. Calculate the % abundance of the two isotopes of Ga. A W Ga = 69.723 (Per. table) Ga Let’s name p1 = % of 69Ga and p2 = % of 71Ga. p1 + p2 = 100 then, p1 = 100 − p2 (1) p1 (1) p1 × 68.9257 + p2 × 70.9249 AW = 69.723 = ──────────────────── then, 100 100 6972.3 = p1× 68.9257 + p2× 70.9249 Then, replace p1 by (1) 70.9249 (1) 6972.3 = (100 − p2) × 68.9257 + p2 × 70.9249 6972.3 = 6892.57 − p2 × 68.9257 + p2 × 70.9249 6972.3 6972.3 − 6892.57 = p2 × (70.9249 − 68.9257) 6972.3 6972.3 − 6892.57 6972.3 p2 = ─────────── = 39.88% p2 70.9249 − 68.9257 70.9249 p1= 100 − p2 = 60.12% Atoms and the Mole Atoms A collection term states collection a specific number of specific items. items. • 1 dozen donuts dozen = 12 donuts 12 • 1 ream of paper ream = 500 sheets 500 • 1 case case = 24 cans 24 Atoms and the Mole Atoms A mole is (a collection number) the amount of a mole substance that contains substance • the same number of particles (atoms, the molecules, ions, protons, electrons, etc.) as there are carbon atoms in 12 g of carbon-12 isotope isotope • 1 mol = 6.022 x 1023 particles (Avogadro’s number). Amadeo Avogadro number). • The number is referred to the atomic mass The assigned to carbon-12 isotope. assigned Atoms and the Mole Atoms 1 mole of … Number of particles Number 1 mole C mole = 6.022 x 1023 C atoms 1 mole Na mole = 6.022 x 1023 Na atoms 1 mole Au = 6.022 x 1023 Au atoms 1 mole electrons = 6.022 x 1023 electrons 1 mole H2O = 6.022 x 1023 H2O molecules 1 mole Na+ = 6.022 x 1023 Na+ ions Molar Mass Molar The molar mass of any element is the mass in The molar grams of 6.022 x 1023 atoms of that element, grams i.e., one mole of the element. mole Molar mass is abbreviated M, has units of Molar has grams per mole (g/mol), and is numerically (g/mol), equal to the atomic weight of the element (periodic table). Molar mass of Na = 22.990 g/mol Molar 22.990 Molar mass of Cl = 35.453 g/mol Molar 35.453 Molar mass of O = 15.999 g/mol Molar 15.999 Conversion factors Conversion Avogadro’s number 6.022 x 1023 can be written as 6.022 equalities and conversion factors. equalities Equality: 1 mole = 6.022 x 1023 particles = molar mass (g) Conversion Factors: particles = atoms or molecules 6.022 x 1023 particles and 1 mole 1 mole 6.022 x 1023 particles mole 6.022 x 1023 particles molar mass (g) and 1 mole molar mass (g) and molar mass (g) 6.022 x 1023 particles molar mass (g) 1 mole Converting moles ↔ mass Moles to mass Moles g moles x ──── = grams moles ──── 1 mol Mass to moles 1 mol mol g x ────= moles ────= grams The molar mass as conversion factors molar What is the mass of silicon represented by What 0.250 moles of this element? M of Si = 28.086 28.09 g g/mol 0.250 moles x ────── = 7.02 g Si ────── How many moles of manganese are 19.36 g of of that metal? M of Mn = 54.938 g/mol that 1 mol 19.36 g x ───── = 0.352384 = 0.3524 moles ───── 0.3524 54.938 g 54.938 4 SF How many atoms of calcium are in 4.008 g of that metal? that M of Ca = 40.08 g/mol 1 mol 6.022 x 1023 atoms mol 4.008 g x ────── x ───────────── ────── ───────────── 40.08 g 1 mol 40.08 The density of Au is 19.32 g/cm3. What is the The What volume of a piece of gold that contains 2.6 x 1024 volume atoms? If the piece of metal is a square with a thickness of 0.10 cm, what is the length (in cm) of one side of the square? AW = 196.97 g/mol AW 196.97 g Au 196.97 2.6 x 1024 atoms Au x ──────────── = 850 g Au ──────────── 6.022 x 1023 atoms 6.022 1 cm3 cm 850 g Au x ──────── = 43 cm3 Au 850 ──────── 19.32 g Au 19.32 side = l V = th x A = th x l 2 th thickness (th) thickness l = SQRT (V/th) = SQRT (43 cm3 / 0.10 cm) = 21 cm (43 l What is the average mass of one germanium atom? M Ge = 72.59 g/mol Here we have to divide the mass of a mole by the number of atoms in that mole. mole. 1 mole Ge = 72.59 g = 6.02 x 1023 atoms mole 72.59 g Ge 1 mol Ge g Ge 72.59 ─────── x ───────────── = 1.205 x10-22 ───── ───────────── ───── 1 mol Ge 6.022 x1023 atoms Ge 1 atom Ge mol 0.0000000000000000000001205 g !!!!!!! 0.0000000000000000000001205 Periodic Table(*) Periodic • a listing of the elements arranged according listing to their chemical and physical properties to • elements are arranged according to similar elements properties. • Groups or families contain elements with Groups similar properties in vertical columns. columns • periods are horizontal rows of elements. rows Every period has a number (row) from 1 through 7. through (*) originally Mendeleev by atomic mass (1869), (*) atomic later Moseley by increasing atomic number increasing (1913). (1913). Periodic Table Periodic Groups • • • • • • referred to by number or top element some have names: some The Representative Elements The alkali metals - group 1A alkaline earth metals - group 2A noble gases - group 8A halogens - group 7A • chalcogens - group 6A • pnictogens - group 5A Alkali Metals Group 1A(1), the alkali metals, includes alkali includes lithium, sodium, potassium, rubidium, cesium, and francium cesium, ChemNow 2.17 Exercise Halogens Halogens Group 7A(17) the halogens, halogens includes fluorine, chlorine, bromine, and iodine. iodine. Representative Elements Representative 1 1A 11 1.008 3 2 2A 4 Li Be H 6.941 9.012 11 12 Na 22.99 19 K 13 3A 5 B 24.31 20 3 3B 21 Ca Sc Mg 4 4B 22 5 5B 23 Ti V Zr Nb 6 6B 24 Cr Cr 102.9 77 106.4 78 107.9 112.4 79 80 114.8 81 118.7 82 121.8 83 127.6 84 126.9 85 131.3 86 195.1 197.0 Pb Bi 68 Unp Unh (227) (257) (260) Mo W (263) Tc (98) 75 Re 186.2 107 Uns (262) Ru Os 190.2 108 Uno (265) Rh Ir 192.2 109 Une (266) Pd Pt Au Hg In Tl 200.6 204.4 Sn 58 59 60 61 62 63 64 65 66 67 Pr Nd Pm Sm Eu Gd Tb Dy Ho 140.1 90 140.9 91 144.2 92 232.0 (231) 238.0 Pa U (147) 93 Np (237) 150.4 94 Pu (242) 152.0 95 Am (243) 157.3 96 Cm (247) 158.9 97 Bk (247) 162.5 98 Cf (249) Sb 207.2 209.0 Ce Th Kr 101.1 76 Unq Ra Br 95.94 74 Ac (226) Fr Se Ar 39.95 36 83.80 54 183.8 106 (223) As Cl 35.45 35 79.90 53 180.9 105 Ta Cd Ge S 32.07 34 78.96 52 178.5 104 Hf Ag Ga P 30.97 33 74.92 51 138.9 89 La Zn Si 28.09 32 72.59 50 91.22 92.91 72 73 Ba Cu Al 26.98 31 69.72 49 88.91 57 137.3 88 12 2B 30 Ne 20.18 18 63.55 65.39 47 48 87.62 56 Cs Ni 11 1B 29 F 19.00 17 He 4.003 10 58.69 46 85.47 55 132.9 87 Co 10 8B 28 O 16.00 16 17 7A 9 58.93 45 47.88 50.94 40 41 Y Fe 9 8B 27 N 14.01 15 16 6A 8 55.85 44 40.08 44.96 38 39 Sr Mn 8 8B 26 C 12.01 14 15 5A 7 52.00 98 54.94 42 43 39.10 37 Rb 7 7B 25 10.81 13 14 4A 6 18 8A 2 164.9 99 Es (254) Er 167.3 100 Fm (253) Te Po (210) I At Xe Rn (210) (222) 69 70 71 Tm Yb 168.9 101 Md (256) 173.0 102 No (254) Lu 175.0 103 Lw (257) Transition Elements Transition 1 1A 11 1.008 3 2 2A 4 Li Be H 6.941 9.012 11 12 Na 22.99 19 K 13 3A 5 B 24.31 20 3 3B 21 Ca Sc Mg 4 4B 22 5 5B 23 Ti V Zr Nb 6 6B 24 Cr Cr 102.9 77 106.4 78 107.9 112.4 79 80 114.8 81 118.7 82 121.8 83 127.6 84 126.9 85 131.3 86 195.1 197.0 Pb Bi 68 Unp Unh (227) (257) (260) Mo W (263) Tc (98) 75 Re 186.2 107 Uns (262) Ru Os 190.2 108 Uno (265) Rh Ir 192.2 109 Une (266) Pd Pt Au Hg In Tl 200.6 204.4 Sn 58 59 60 61 62 63 64 65 66 67 Pr Nd Pm Sm Eu Gd Tb Dy Ho 140.1 90 140.9 91 144.2 92 232.0 (231) 238.0 Pa U (147) 93 Np (237) 150.4 94 Pu (242) 152.0 95 Am (243) 157.3 96 Cm (247) 158.9 97 Bk (247) 162.5 98 Cf (249) Sb 207.2 209.0 Ce Th Kr 101.1 76 Unq Ra Br 95.94 74 Ac (226) Fr Se Ar 39.95 36 83.80 54 183.8 106 (223) As Cl 35.45 35 79.90 53 180.9 105 Ta Cd Ge S 32.07 34 78.96 52 178.5 104 Hf Ag Ga P 30.97 33 74.92 51 138.9 89 La Zn Si 28.09 32 72.59 50 91.22 92.91 72 73 Ba Cu Al 26.98 31 69.72 49 88.91 57 137.3 88 12 2B 30 Ne 20.18 18 63.55 65.39 47 48 87.62 56 Cs Ni 11 1B 29 F 19.00 17 He 4.003 10 58.69 46 85.47 55 132.9 87 Co 10 8B 28 O 16.00 16 17 7A 9 58.93 45 47.88 50.94 40 41 Y Fe 9 8B 27 N 14.01 15 16 6A 8 55.85 44 40.08 44.96 38 39 Sr Mn 8 8B 26 C 12.01 14 15 5A 7 52.00 98 54.94 42 43 39.10 37 Rb 7 7B 25 10.81 13 14 4A 6 18 8A 2 164.9 99 Es (254) Er 167.3 100 Fm (253) Te Po (210) I At Xe Rn (210) (222) 69 70 71 Tm Yb 168.9 101 Md (256) 173.0 102 No (254) Lu 175.0 103 Lw (257) Colors of solutions of Transition Metal Compounds Transition Inner Transition Elements Inner 1 1A 11 1.008 3 2 2A 4 Li Be H 6.941 9.012 11 12 Na 22.99 19 K 13 3A 5 B 24.31 20 3 3B 21 Ca Sc Mg 4 4B 22 5 5B 23 Ti V Zr Nb 6 6B 24 Cr Cr 102.9 77 106.4 78 107.9 112.4 79 80 114.8 81 118.7 82 121.8 83 127.6 84 126.9 85 131.3 86 195.1 197.0 Pb Bi 68 Unp Unh (227) (257) (260) Mo W (263) Tc (98) 75 Re 186.2 107 Uns (262) Ru Os 190.2 108 Uno (265) Rh Ir 192.2 109 Une (266) Pd Pt Au Hg In Tl 200.6 204.4 Sn 58 59 60 61 62 63 64 65 66 67 Pr Nd Pm Sm Eu Gd Tb Dy Ho 140.1 90 140.9 91 144.2 92 232.0 (231) 238.0 Pa U (147) 93 Np (237) 150.4 94 Pu (242) 152.0 95 Am (243) 157.3 96 Cm (247) 158.9 97 Bk (247) 162.5 98 Cf (249) Sb 207.2 209.0 Ce Th Kr 101.1 76 Unq Ra Br 95.94 74 Ac (226) Fr Se Ar 39.95 36 83.80 54 183.8 106 (223) As Cl 35.45 35 79.90 53 180.9 105 Ta Cd Ge S 32.07 34 78.96 52 178.5 104 Hf Ag Ga P 30.97 33 74.92 51 138.9 89 La Zn Si 28.09 32 72.59 50 91.22 92.91 72 73 Ba Cu Al 26.98 31 69.72 49 88.91 57 137.3 88 12 2B 30 Ne 20.18 18 63.55 65.39 47 48 87.62 56 Cs Ni 11 1B 29 F 19.00 17 He 4.003 10 58.69 46 85.47 55 132.9 87 Co 10 8B 28 O 16.00 16 17 7A 9 58.93 45 47.88 50.94 40 41 Y Fe 9 8B 27 N 14.01 15 16 6A 8 55.85 44 40.08 44.96 38 39 Sr Mn 8 8B 26 C 12.01 14 15 5A 7 52.00 98 54.94 42 43 39.10 37 Rb 7 7B 25 10.81 13 14 4A 6 18 8A 2 164.9 99 Es (254) Er 167.3 100 Fm (253) Te Po (210) I At Xe Rn (210) (222) 69 70 71 Tm Yb 168.9 101 Md (256) 173.0 102 No (254) Lu 175.0 103 Lw (257) • rows = periods • gradual transition in gradual properties from metallic to nonmetallic moving from left to right across a period to Metals Metals • Malleable: can be hammered or pressed Malleable: into new shapes (coins, rings, etc.) into • Ductile: can be pressed, beaten, or drawn Ductile: into shape when cold (wires, such as Cu) into • solid at room temperature (except for Hg) • luster • photoelectric effect (e– emission due to light) light) • thermionic effect (e– emission due to heat) • readily lose electrons readily lose • good thermal and electrical conductors Nonmetals Nonmetals • • • • • • • solid, liquid, or gas brittle if solid (fracture) non-malleable, non-ductile thermal and electrical insulators do not exhibit photoelectric effect do not exhibit thermionic effect readily gain electrons readily gain Metalloids (Semimetals) Metalloids • properties intermediate to those of properties metals and nonmetals metals • are located around the solid ladder are between metals and non-metals in periodic table periodic • B, Si, Ge, As, Sb, Te, Po, At Noble gases Noble • Are the least reactive elements • Are gases, none-abundant on Earth, Are but He is the second in the universe after hydrogen • Neon in advertising signs Neon • Some lasers are made of He, Ar, Kr Learning Check Learning Identify each of the following elements as Identify 1) metal 2) nonmetal 3) metalloid A. sodium A. B. chlorine C. silicon C. D. iron E. carbon F. antimony ____ ____ ____ ____ ____ ____ ____ Learning Check Learning Match the elements to the description. A. Metals in Group 4A(14) A. 1) Sn, Pb 2) C, Si 1) 3) C, Si, Ge, Sn B. Nonmetals in Group 5A(15) 1) As, Sb, Bi 2) N, P 3) N, P, As, Sb C. Metalloids in Group 4A(14) 1) C, Si, Ge, 2) Si, Ge 3) Si, Ge, Sn, Pb 1) Learning Check Learning The elements magnesium and calcium are in what The group? a. alkali metals b. alkaline earth metals a. c. halogens d. noble gases Which elements are nonmetals? Which a. sodium and potassium a. b. magnesium and barium c. boron and aluminum d. carbon and bromine Identify the period number for the row that ends in Identify argon. a. Period 1 b. Period 2 c. Period 3 d.Period 4 a. Learning Check Learning Which statement is characteristic of metals? A. They are shiny. A. B. They are poor conductors of electricity. C. They melt at high temperatures. a. statement A only b. statements A and B only c. statements A, B, and C c. d. statements A and C only Which statement is false? A. Potassium is an alkali metal. A. B. Strontium is an alkaline earth metal. C. Argon is a noble gas. D. Zinc in a halogen. Learning Check Learning What is the right order of increasing metallic What character for the elements Rb, F, P, Ga? character Rb < F < P < Ga P < F < Rb < Ga Ga< Rb < P < F F < P < Ga < Rb Learning Check Learning How many atoms are in 1.50 mol Na? A.1.50 b. 9.03x1023 c. 3.00 d. 2.49x10-24 e. 345 6.022× 1023 atoms 6.022 1.50 mol × ──────────── = 9.03 x 1023 atoms 9.03 1 mol mol How many moles of Ar in 5.22 x 1022 atoms of this noble gas? a. 11.5 b. 0.0867 c. 1.15x10 22 noble d. 8.67x1023 d. e. 3.14 x1046 1 mol mol 5.22 x 1022 atoms × ──────────── = 0.0867 mol 5.22 ──────────── 6.022× 1023 atoms 6.022 Learning Check Learning What is the mass (grams) of one atom of Na? a. 22.99 1 mol Na mol b. 0.04350 c. 3.818 x 10−23 b. 2.619x1022 22.99 g 22.99 ─────────── = 3.818 x 10−23 g/atom 3.818 g/atom 6.022× 1023 atoms 6.022 ...
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This note was uploaded on 11/07/2011 for the course CHM 2045 taught by Professor Geiger during the Fall '08 term at University of Central Florida.

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