2Atomic theoryJohn Dalton, 1808: matter is made of tiny indestructible particles called atomsWhat evidence persuaded John Dalton that matter was made of atoms?
3Evidence for Atoms Boyle’s Law (1660s) Gases can be compressed (PV = constant)Suggests that a gas is made of particles with space betweenConservation of mass (Lavoisier, 1789)In a chemical reaction, matter is neither created nor destroyed
4Evidence for Atoms Law of Definite Proportions (Proust, 1797) All samples of a compound, regardless of source or how prepared, have the same proportions of their constituent elements (constant composition)Law of Multiple Proportions (Dalton, 1803)When two elements (A and B) form two different compounds, the masses of B that combine with 1 g of A can be expressed as a ratio of small whole numbers.
6Evidence for Atoms Combining Volumes of Gases When two gases combine to form a new compound, the volumes that combine will be in a ratio of small whole numbers.
7A New System of Chemical Philosophy: John Dalton, 1808 Each element is composed of tiny indestructible particles called atoms.All atoms of a given element have the same mass and other properties that distinguish them from the atoms of other elements.Atoms combine in simple, whole-number ratios to form compounds.Atoms of one element cannot change into atoms of another element. In a chemical reaction, atoms change the way that they are bound together with other atoms to form a new substance.
9Discovery of the electron J.J. Thompson (1897)Cathode rays are deflected by an electric or magnetic fieldCathode ray = beam of negatively charged particles (electrons) coming out of cathode metal atomsDetermined electron mass-to-charge ratio = – x 10–9 g/C
14The gold foil experiment Ernest Rutherford (1910)Bombarded gold foil with alpha particlesMost went straight throughSome slightly deflectedA few strongly deflected“about as credible as if you had fired a 15-inch shell at a piece of tissue paper, and it came back and hit you”
16Rutherford’s nuclear model Mass & positive charge concentrated in nucleusMost particles miss the nucleus & are not deflected: most of the atom is empty spaceSome particles come near the nucleus & are deflected: nucleus is positively charged and very denseTiny, lightweight electrons circle the nucleus, like planets around the sun
17Composition of the atom Protons+1 chargex 10–24 g = amuNeutrons0 chargex 10–24 g = amuElectrons–1 chargex 10–24 g = amu
18Atomic number and mass number Atomic number (Z) = protonsMass number (A) = protons + neutronsA 35Cl atom has 17 protons and 18 neutronsAlso shown as chlorine-35
19Ion chargeWhen an atom loses or gains an electron, it becomes an ionIon charge is shown in the upper right corner of the atomic symbolIf no charge is shown, the charge is zeromass number, Aprotons + neutrons2311Na1+ion chargeprotons – electronsatomic number, Zprotons
20Give the structure (p+, n0, e–) of these atoms 40K1+235U34S2–
21Give the symbol of each atom or ion 35 p+, 44 n0, 36 e–79Br1–47 p+, 62 n0, 46 e–109Ag1+26 p+, 28 n0, 26 e–54Fe
22IsotopesAtoms with the same number of protons but different numbers of neutrons are isotopes of the same element6Li and 7Li are isotopes of lithiumBoth are the element lithium6Li has 3 protons, 3 neutrons7Li has 3 protons, 4 neutrons
25Average atomic massElement’s atomic mass = weighted average of masses of all naturally-occurring isotopes of that element
26Average Atomic Mass Calculate the average atomic mass of Ne: ISOTOPE ISOTOPIC MASS (amu) ABUNDANCE20Ne amu %21Ne amu %22Ne amu %
27Average Atomic Mass Calculate the average atomic mass of Ne: ISOTOPE ISOTOPIC MASS (amu) ABUNDANCE20Ne amu %21Ne amu %22Ne amu %(0.9048)( amu) = amu(0.0027)( amu) = amu(0.0926)( amu) = amu20.18 amu
28How to calculate the average atomic mass Magnesium occurs as three isotopes: 24Mg, mass amu (78.99%) 25Mg, mass amu (10.00%) 26Mg, mass amu (11.01%)The average atomic mass of Mg is ( x ) + ( x ) + ( x ) = amuBe careful about sigfigs!
29Atomic massTwo natural isotopes of antimony exist % exists as 121Sb (mass amu), and the rest is 123Sb (mass amu). What is the atomic mass of antimony?The abundances must total 100%, so abundance of 123Sb = 100 – 57.3 = 42.7%(0.573 x ) + (0.427 x ) = = amu
30Percent abundanceTwo natural isotopes of copper exist, 63Cu ( amu) and 65Cu ( amu). What is the abundance of each isotope?The abundances must total 100%If x = 63Cu abundance, then 65Cu = 1–xAverage mass (from periodic table) = amu
31Percent abundance 63Cu = 69.15% and 65Cu = 30.85% x = 63Cu ( amu) & 1–x = 65Cu ( amu)Average mass = amu63Cu = 69.15% and 65Cu = 30.85%
32A unit for counting atoms We have units for describing mass, volume, temperature, and so forth, butwe need a unit for counting the number of itemsFor large items like eggs or donuts, we can use dozen: one dozen = 12 itemsFor tiny items like atoms or molecules, we need the mole!
33What is a mole?One mole is defined as the number of atoms in exactly 12 grams of 12COne mole contains x 1023 particlesThis number is called Avogadro’s number (NA)There is Avogadro’s number of particles in a mole of any substance
34Calculations with Avogadro How many atoms of gold are present in mol Au?How many moles of Pb atoms are 8.27 x 1022 atoms of Pb?
35Mass on the periodic table One atom of Clweighs35.45 amuOROne mole of Cl atoms weighs gramsThe molar mass of Cl is g/mol
36Calculations with molar mass What is the mass of 1.38 mol Al?How many moles are in 35 g of Zn?
37Chemistry toolbox You now have 2 mole tools in your toolbox: Avogadro’s number6.02 x 1023 particles = 1molRelationship between particles (atoms/molecules) & molesMolar massThe atomic mass on the periodic table, in grams = 1 molRelationship between grams & moles
38Avogadro and molar mass What is the mass of 2.35 x 1024 atoms of Cu?
39Avogadro and molar mass How many He atoms are present in a 22.6 g sample of He gas?
40Mole concept Examples 2-7A, 2-7B, 2-8A, 2-8B How many atoms of gold are present in 5.07 x 10–3 mol Au?How many 206Pb atoms are present in 8.27 x 10–3 mol of Pb? (Pb contains 24.1% 206Pb )What is the mass of 2.35 x 1024 atoms of Cu?How many He atoms are present in a 22.6 g sample of He gas?
41Mole concept Examples 2-9A and 2-9 B How many Pb atoms are in a piece of lead with volume cm3? Density of Pb = g/cm30.100 mg of Re contains 2.02 x 1017 atoms of 187Re. What is the percent abundance of 187Re in this sample?
42Exercise 30Show that mass is conserved within experimental error in this experiment:10.00 g calcium carbonate was dissolved in mL hydrochloric acid (d = g/mL). The products were g solution and 2.22 L carbon dioxide gas (d = g/L)
43Exercise 31In one experiment, 2.18 g sodium were reacted with g chlorine. All the sodium was used up, and 5.54 g sodium chloride were produced. In a second experiment, 2.10 g chlorine were reacted with g sodium. All the chlorine was consumed, and 3.46 g sodium chloride were produced. Are these results consistent with the law of constant composition?
44Exercise 38 In an experiment like the oil drop experiment, drop 1 carried a charge of 6.41 x 10–19 Cdrop 2 had 1/2 the charge of drop 1drop 3 had twice the charge of drop 1drop 4 had a charge of 1.44 x 10–18 Cdrop 5 had 1/3 the charge of drop 4Do these data support the value of x 10–19 C for the electron charge? Could Millikan have inferred the electron charge from these data?
45Exercise 42 For the ion 228Ra2+, with a mass of 228.030 u, determine The numbers of protons, neutrons, and electronsThe ratio of the mass of this atom to that of an atom of 16O ( u)
46Exercise 49 There are three naturally occurring isotopes of magnesium: Calculate the weighted average atomic mass of magnesium.
47Exercise 54Boron has a weighted average atomic mass of u. What are the percent natural abundances of its two isotopes, 10B ( u) and 11B ( u)?
48Exercise 58 Determine The number of Ar atoms in 5.25 mg argon The molar mass of an element if the mass of 2.80 x 1022 atoms of that element is 4.24 gThe mass of a sample of aluminum that contains the same number of atoms as g zinc
49Exercise 60What is the total number of atoms present in a 75.0 cm3 sample of plumber’s solder, an alloy containing 67% Pb and 33% Sn by mass and having a density of 9.4 g/cm3?
50Early Observations of Mass 1770s Lavoisier - Conservation of MatterCareful measurements showed that mass is neither created nor destroyed in a chemical reaction.The total mass before and after reaction is the same
51Conservation of mass Examples 2-1A and 2-1B A g sample of magnesium reacts with g nitrogen gas. The sole product is magnesium nitride. After the reaction the mass of unreacted nitrogen is g. What mass of magnesium nitride was produced?A 7.12g sample of magnesium is heated with 1.80 g of bromine. All the bromine is consumed and 2.07 g of magnesium bromide is the only product. What mass of magnesium is left over?
52Early Observations of Matter 1799 Proust - Constant CompositionAll samples of a given compound contain exactly the same proportion of elements by mass.This is the Law of Definite Proportions
53Constant composition Examples 2-2A and 2-2B This information was provided in the example:A g sample of magnesium combines with oxygen to yield g magnesium oxideWhat is the mass of magnesium in g of magnesium oxide?You wish to make exactly 2.00 g of magnesium oxide. What masses of magnesium and oxygen must you combine?
54Early Observations of Matter 1803 John Dalton - Law of Multiple ProportionsWhen the same elements form different compounds, the combining ratios in the compounds are always in a whole number relationship.Compound II has exactly twice as much O per C as compound I, by massmass of Oxygenreacting w/ 1 g of Carboncmpd I g O/g Ccmpd II g O/g C
56The Electron: Part I J.J. Thompson - 1897 Cathode rays can be deflected by electric and magnetic fieldsThe charge-to-mass ratio of an electron can be determined: 1.76 x 108 C/g
57Cathode Rays Deflected by Thomson (1897)Cathode Rays Deflected byElectric Field
58Cathode Rays Deflected by Thomson (1897)Cathode Rays Deflected byMagnetic Field
59Balancing Deflections: Thomson (1897)Balancing Deflections:Measures the e/m Ratio
60Millikan’s Oil-drop Experiment Determines the charge of one electron
61RadioactivitySome elements spontaneously emit radiation called radioactivityThree types of radioactivity:Alpha (a) = He2+Beta (b) = e1–Gamma (g) = no mass or chargeMarie Curie1876–1934
62Alpha Particle Scatter Explained Rutherford’s Nuclear Model
63Atomic composition Examples 2-3A and 2-3B Write an appropriate symbol for the species with 47 protons, 61 neutrons, and 47 electronsDetermine the numbers of protons, neutrons, and electrons in an ion of sulfur-35 that carries the charge 2–
64Atomic MassesCalculate the atomic mass of copper, Cu, from the following data:ISOTOPE ISOTOPIC MASS (amu) ABUNDANCE63Cu amu %65Cu amu %
65Atomic MassesCalculate the atomic mass of copper, Cu, from the following data:ISOTOPE ISOTOPIC MASS (amu) ABUNDANCE63Cu amu %65Cu amu %63Cu: x =65Cu: x =63.5the average atomic mass of Cu is 63.5 amu
66Periodic TableDmitri Mendeleev developed the modern periodic table in 1869,based on his belief that element properties are periodic functions of their atomic massesWe now know that element properties are periodic functions of their ATOMIC NUMBERS