Why study chemistry - University of Nebraska Omaha

1、Measurements PHILOSOPHY OF SCIENCE Foundational assumptions Physical phenomena are repeatable. Relationships exist between quantities and their changes. We can perform experiments to find these relationships. We can use mathematics to create statements (theories) about of many of these relationships

2、. - Unfortunately not all relationships can be expressed mathematically, especially in chemistry. Scientific method Experiment data doesnt fit an accepted theory. Theory is created or modified to include explain new results. New experiments are done to test theory. Hypothesis statement made before e

3、xperiment attempting to predict result. As long as theory is confirmed, it is accepted as true. (Fundamental theories are called laws.) When new experimental data doesnt fit theory, the process starts again! MEASUREMENTS Measurements are needed to explore relationships between quantities. Relationsh

4、ips can be qualitative. The top of campanile is higher than the library. Illiteracy contributes to poverty. Daddy is taller than Mary Grace. Daddy is taller than Sarah. Note: These qualitative relationships limit knowledge about Mary Grace and Sarah. Relationships are more powerful when they are qua

5、ntitative. Daddy is 75 inches. Mary Grace is 62 inches. Sarah is 46 inches. All measurements need units! Temperature in Edmonton is 20. Gasoline in Edmonton costs 1.51. *Measurements without units are meaningless.* MATTER Conservation of Mass States of Matter Gas Liquid Solid CLASSIFICATIONS OF MATT

6、ER I. Homogeneous A. Pure substances 1. Elements 2. Compounds B. Solutions II. Heterogeneous OR I. Pure substances A. Elements B. Compounds II. Mixtures A. Solutions B. Heterogeneous PROPERTIES OF MATTER (intensive and extensive) CHANGES IN MATTER UNITS OF MEASUREMENT TEMPERATURE (Memorize 273.15) S

7、I PREFIXS (f- through T-) DERIVED SI UNITS ACCURACY AND PRECISION SIGNIFICANT FIGURES DIMENSIONAL ANALYSIS Learning objective 1.2 The student is able to select and apply mathematical routines to mass data to identify or infer the composition of pure substances and/or mixtures. (See SP 2.2; Essential

8、 Knowledge 1.A.2) DENSITY Definition: - one can think of density as a conversion factor between mass and volume mass density volume Example: An Olympic shot put weighs 16.0 lbs. If the shot put is made of iron, what is its volume? d(Fe) = 7.86 g/cm3 1 lb = 0.4536 kg Example: What is the mass of osmi

9、um in units of pounds that has a volume of 65.45 in3 (the size of a tennis ball) if the density of osmium is 22.61 g/cm3? Osmium is very hard; thus, it is used (alloyed with iridium) in high quality pen tips. It is the densest element. Example: Water is placed in a 100 mL graduated cylinder and its

10、initial volume 34.2 mL. A 250 mL beaker is weighed to be 116.679 g. Some metal shavings are placed in the beaker. The mass of the beaker and the shavings is 170.503 g. When the shavings are poured into the 100 mL graduated cylinder, the volume rises to 54.2 mL. Given the table of densities below, de

11、termine the unknown metal. Show work! MgAlFeCuAgPb d(g/cm3) 1.74 2.70 7.87 8.96 10.5 11.3 Therefore, the metal shavings are aluminum. m170.503g 116.679g53.824g2.69g d V54.2mL34.2mL20.0mLmL Basic Atomic Structure / Nomenclature Learning objective 1.1 The student can justify the observation that the r

12、atio of the masses of the constituent elements in any pure sample of that compound is always identical on the basis of the atomic molecular theory. (See SP 6.1; Essential Knowledge 1.A.1) FUNDAMENTAL LAWS OF CHEMISTRY Lavoisiers Fundamental Laws of Chemistry -Father of Modern Chemistry -Late 18th ce

13、ntury French aristocrat -Guillotined during the French Revolution. 1. Law of Mass Conservation -In any chemical processes, matter cannot be created or destroyed. 2. Law of Definite Composition -A chemical compound always has the same mass composition regardless of its source. Daltons Atomic Theory -

14、 Early 19th century British scientist 1.All matter is made of indivisible atoms. 2.Elements are made of one type of atom. -All atoms have the same chemical and physical properties (mostly). 3.Compounds are made of atoms in fixed proportions. -Cant use of an atom to make a compound. -Also stated as L

15、aw of Multiple Proportions. 4.Atoms change arrangement in a chemical reaction, not identity. Law of Multiple Proportions When two elements combine to form two or more compounds, the ratio formed from each compounds mass ratio always yields a fraction. - In other words, elements cannot combine togeth

16、er with random compositions. The number of atoms of each element in a compound must be a whole number. Example: Consider two compounds of sulfur and oxygen. Compound A has a mass composition of 49.9% oxygen and 50.1% sulfur. Compound B has a mass composition of 59.9% oxygen and 40.1% sulfur. The oxy

17、gen to sulfur ratio for compound A is The oxygen to sulfur ratio for compound B is The law of multiple proportions says that a ratio of these ratios must yield a simple fraction. 0.99602 0.6667 1.4943 Compound A has two-thirds the oxygen that compound B has. Modern analysis yields that compound A =

18、SO2 and compound B = SO3. 49.9 0.9960 50.1 59.9 1.494 40.1 ATOMIC STRUCTURE HISTORY 1897 J.J. Thomson 1909 Robert Millikan 1910 Ernest Rutherford ATOMIC STRUCTURE Two components of an atom Nucleus (pl. nuclei) Electrons e- Definition: 1 Angstrom () = 10-10 m Learning objective 1.14 The student is ab

19、le to use data from mass spectroscopy to identify the elements and the masses of individual atoms of a specific element. (See 1.4, 1.5; Essential Knowledge 1.D.2) NUCLEAR STRUCTURE Two components of nucleus Proton p+ Neutron n NEW ATOMIC STRUCTURE HISTORY continued 1932 James Chadwick - Showed that

20、atoms have a third particle different than the electron and proton. - Aimed a beam of alpha particles (4He nuclei) at a sheet of beryllium to produce uncharged particles. - Interacting these uncharged particles with other nuclei showed that they must have approximately the same mass as a proton. - W

21、on Nobel Prize in 1935 ATOMIC SYMBOLS - Z A Sy Atomic Number - Z Mass Number A Definition: isotope an atom with the same atomic number as another atom but a different mass number. MASS SPECTROMETRY - Modern method for measuring masses of atoms (or molecules) - Sample of atoms (or molecules) is vapor

22、ized and ionized by hitting it with an electron beam - Ionized atoms travel into a region with a magnetic field - The magnetic field causes the path gaseous ion to curve - The amount of curvature for the path depends on the charge and the mass - Since the charge is fairly easy to guess (usually eith

23、er +1 or +2), the curvature of the path yields the mass of the atom./wiki/Mass_spectrometry NEW - Mass spectroscopy yields information about isotopic abundances as well as precise masses. - Rubidium has two naturally occurring isotopes (85Rb, 72% and 87Rb, 28%). - Tin has ten(!

24、) naturally occurring isotopes (from 112Sn to 124Sn). 0 5 10 15 20 25 30 35 85 88 91 94 97 100 103 106 109 112 115 118 121 124 127 130 133 136 139 142 145 148 151 154 157 160 163 Mass spectrum of Sn 0 10 20 30 40 50 60 70 80 45 48 51 54 57 60 63 66 69 72 75 78 81 84 87 90 93 96 99 102 105 108 111 11

25、4 117 120 123 Mass spectrum of Rb DEFINITION OF ATOMIC MASS UNIT ATOMIC AND MOLECULAR MASSES Average Atomic Mass PERIODIC TABLE OF GROUPS OF ELEMENTS Two different classification schemes Metal Nonmetal Scheme (based on physical properties) Metals Nonmetals Metalloids B, Si, Ge, As, Sb, Te At nonmeta

26、lish, Po metalish Group Scheme (based on chemical properties) Alkali metals column 1A (Ashes w/out air) Alkaline earth metals column 2A Pnictogens column 5A(Choke maker) Chalcogens column 6A(Ore maker) Halogens column 7A(Salt maker) Noble gases column 8A Transition metals four rows in middle of tabl

27、e Rare earths bottom two rows beside table Also inner transition metals, lanthanides-actinides, lanthanoids-actinoids CHEMICAL COMPOUNDS Chemical compounds consist of 1.) molecules - hydrocarbons compounds with only carbon and hydrogen. Molecular Elements - gases: H2, N2, O2, F2, Cl2(diatomic) - liq

28、uid: Br2 - solids: P4, S8, Se8, I2 - allotropes different substances made from a single element - oxygen, O2; ozone, O3 - graphite, C sheets; diamond, C network - white phosphorus, P4; red phosphorus, chains of tetrahedra; violet P; black P - orthorhombic sulfur, S8; polymeric sulfur, Sx; many other

29、s - white tin, ductile; grey tin, brittle (transition temp = 13.2 C) 2.) ions EMPIRICAL FORMULA - lowest integer ratios between atoms NOMENCLATURE: Nomenclature of ions Cations (positive) - name of ion is same as metal - with main group metals, Roman numerals are used to indicate the charge of the i

30、on only if the metal can have more than one charge. - with transition metals, the charge of cation is indicated with Roman numerals - many transition metals have only one common charge; thus, using the roman numeral is optional. - Sc3+, Ni2+, Zn2+, Ag+, Cd2+, La3+ - polyatomic cations are given ium

31、suffix Anions (negative) - monatomic anions have ide suffix - polyatomic ions with oxygen (oxyanions) have ite or ate suffix -ite is always one less oxygen than -ate *exceptions* OH-hydroxide CN-cyanide peroxide 2 2 O Note: assume peroxides form only with alkali and alkaline earth metals. NAMING ION

32、IC COMPOUNDS 1. Write name of cation first (include Roman numeral, if necessary). 2. Write name of anion. NAMING MOLECULAR COMPOUNDS 1. Write the name of the element that is farthest from upper right-hand corner first. 2. Indicate number of atoms with numerical prefix. 1 mono*6 hexa 2 di7 hepta 3 tr

33、i8 octa 4 tetra9 nono 5 penta 10 deca *use of the mono prefix is not preferred, except for carbon monoxide.* 3. Add name of second element with ide suffix. 4. Indicate number of atoms with numerical prefix. 5. Note: No numerical prefixes are needed for hydrogen. NOMENCLATURE OF ACIDS Binary acids Hy

34、X 1. Write the prefix hydro- 2. Write the name of nonmetal anion with ic suffix 3. Add the word acid Oxyacids 1. Write the name of the anion 2. Change suffix a) change ate to ic b) change ite to ous 3. Add word acid NOMENCLATURE OF HYDRATES 1. Name compound with previously stated rules. 2. At the en

35、d, add the word hydrate with the appropriate numerical prefix. Polyatomic Ion List Monatomic Anions N3-nitrideO2-oxideF-fluoride P3-phosphide S2-sulfideCl-chloride As3-arsenideSe2-selenideBr-bromide H-hydride Te2-tellurideI-iodide Common Metal Ions (alkali and alkaline earth metals not included) Cu+

36、Copper (I)Cu2+Copper (II) Hg22+Mercury (I)Hg2+Mercury (II) Fe2+Iron (II)Fe3+Iron (III) Co2+Cobalt (II)Co3+Cobalt (III) Pb2+Lead (II)Pb4+Lead (IV) Sn2+Tin (II)Sn4+Tin (IV) Mn2+Manganese (II) Mn4+Manganese (IV) Cr3+Chromium (III)Cr6+Chromium (VI) Ag+Silver Zn2+ZincCd2+Cadmium Ni2+Nickel Al3+AluminumGa

37、3+Gallium Sc3+ScandiumLa3+Lanthanum Polyatomic Ions Charge 2+ Hg22+mercury (I) Charge 1+ NH4+ammonium Charge 1- NO2-nitriteNO3-nitrate OH-hydroxide CN-cyanide MnO4-permanganate SCN-thiocyanate ClO-hypochloriteClO2-chlorite ClO3-chlorateClO4-perchlorate BrO-hypobromiteBrO2-bromite BrO3-bromateBrO4-pe

38、rbromate IO-hypoioditeIO2-iodite IO3-iodateIO4-periodate C2H3O2-acetate HCO3-hydrogen carbonate (bicarbonate) HSO4-hydrogen sulfate (bisulfate) H2PO4-dihydrogen phosphate Charge 2- SO32-sulfiteSO42-sulfate C2O42-oxalateO22-peroxide CO32-carbonateS2O32-thiosulfate CrO42-chromate Cr2O72-dichromate HPO

39、42-hydrogen phosphate Charge 3- BO33-boratePO43-phosphateAsO43-arsenate Quantum Theory and Atomic Structure THE NATURE OF LIGHT Light is a crossed electric and magnetic field that is oscillating in time. Changing electric field creates a magnetic field and a changing magnetic field creates an electr

40、ic field, etc B E t 2 E cB t Light is self-propagating electromagnetic field. Electric field: 0 EE sin kzt Magnetic field: 0 HH sin kzt y x z - Light is very peculiar in that it is a particle and a wave at the same time. - Our physical intuition tells us that this is impossible. - Waves are spread o

41、ut as in ocean waves - Particles are in one place (localized) as in a bowling ball. Q: How can something be spread out and localized at the same time? A: Who knows? It is a mystery of nature. Supplemental THE WAVE NATURE OF LIGHT - Light moves at a constant speed through a particular medium. - c spe

42、ed of light in a vacuum ( air) - c = 2.997 x 108 m/s (670,000,000 mi/hr) - Waves have two components. - wavelength - (Greek lambda) - distance between wave crests - frequency - (Greek nu) - how often wave crest moves up and down at a single point - number of beats per second: Hertz Hz - 1 Hz = 1 /s

43、= 1 s-1 - think of a boat bouncing up and down on waves - Frequency and wavelength are related = c - if we know , we can calculate - if we know , we can calculate 1 1 sin x() 18.850 x 05101520 1 0.5 0 0.5 1 THE PARTICLE NATURE OF LIGHT - light comes as particles called photons - energy of a photon i

44、s proportional to frequency E = h - h = Plancks constant h = 6.626 x 10-34 J s Photoelectric Effect Light shining on a metal surface may cause electrons to be ejected from the surface. e - Frequency of light needs to be above threshold frequency to induce photoelectric emission. Kinetic energy of el

45、ectrons is proportional to frequency of incident radiation. Kinetic energy of electrons is independent of light intensity. - I.e., microwave laser will not induce photoelectron emission. This independence contradicts wave nature of light. - According to wave nature, energy of electrons should be pro

46、portional to the intensity. Albert Einstein proposed that the electrons are knocked off the surface with a particle of light! - Nobel 1921 The photoelectric effect can be explained as a collision between an electron and a photon. ELECTROMAGNETIC SPECTRUM Name Wavelength Frequency (Hz) Radio300 km to

47、 0.3 m103 109 Microwave30 cm to 1 mm109 3 x 1011 Infrared1.0 mm to 780 nm3 x 1011 4 x 1014 Visible780 nm to 390 nm4 x 1014 8 x 1014 Ultraviolet390 nm to 1 nm8 x 1014 3 x 1017 X-ray10 to 0.06 3 x 1017 5 x 1019 Gamma1.5 to 0.3 ym2 x 1018 - 1033 LINE SPECTRA OF THE ELEMENTS The light emitted by pure el

48、ements has specific energies. - Therefore light of only specific wavelengths can be seen. (i. e., different colors can be seen) - This emitted light is called a line spectrum. (pl. spectra) Line spectra tell us that atoms can only have certain energy levels. - The atoms cannot have any arbitrary val

49、ue of energy. BOHRS MODEL OF THE HYDROGEN ATOM Learning objective 1.12 The student is able to explain why a given set of data suggests, or does not suggest, the need to refine the atomic model from a classical shell model with the quantum mechanical model. (See SP 6.3; Essential Knowledge 1.C.2) His

50、tory - Scientists before Bohr knew atom was made of nucleus and electrons. - They didnt know where the electrons were or how they behaved. - They also knew each element had a distinct line spectrum. 1913 Model - Bohr assumed electrons traveled in orbits around nucleus. - Bohr also assumed that elect

51、rons could only have specific orbits. - Specific orbits were labeled with a quantum number - Energies of orbits are ER n n nH 1 12 34 2 , , , , RH = 2.18 x 10-18 J - Won Nobel Prize 1922 Using the Bohr Model to Calculate Spectra Eatom = Ephoton Ef Ei = h hR nn R hnn H if H if 1111 2222 THE DUAL NATU

52、RE OF MATTER - Bad News: The Bohr model is wrong! - Electrons dont behave like planets. - Electrons have a wave nature that makes them spread out. We have seen that light can behave as a wave and a particle. This dual nature of light is also true for matter. *All matter behaves as a particle and a w

53、ave.* - I. e., an electron, an atom or a baseball all behave like a wave. DE BROGLIE WAVES (MATTER WAVES) All moving particles have a wavelength. Wavelength of particle is inversely proportional to particles momentum. (De Broglies Relation) note: smaller p implies higher higher p implies smaller Rec

54、all: Momentum is defined as mass velocity or p = m v h p Picture of a de Broglie wave - note that the wave is localized somewhat - as wavelength decreases wave becomes more localized (Note: momentum has increased.) In the macroscopic world, objects do not have large enough wavelengths to exhibit wav

55、e-like behavior. Only in the microscopic world (as in the atom) do objects exhibit wave-like behavior. 0.981 0.981 f x( ) 2.992.99x 3210123 1 0.5 0 0.5 1 0.976 0.976 g x( ) 2.9992.999x 3210123 1 0.5 0 0.5 1 Example: Calculate the wavelength of an electron when the electron is moving 2.18 x 106 m/s.

56、me = 9.109 x 10-31 kg h = 6.626 x 10-34 Js 34 10 316 hh6.626x10J s 3.34x10m3.34 pmv9.109x10kg2.18x10 m/s - Note: The wavelength is about the same as the size of the atom. Example: Calculate the wavelength of a baseball moving 60 mi/hr (26.8 m/s). The mass of baseball is 0.14 kg. 342 3434 hh6.626x10J

57、 sJ s 1.8x101.8x10m pmv0.14kg26.8m/skg m - Note: This is an extremely small wavelength, especially when compared to the size of the baseball. To summarize: Microscopic objects when moving become wave-like. Macroscopic objects have a wave-like nature when moving, but the wave nature is insignificant

58、compared to its particle nature. Experimental confirmation for wave-like properties has been found for electron, proton, neutron, hydrogen atom, sodium atom, bucky balls, et al. - matter waves interfere with each other just like light waves (or any wave) WAVE-PARTICLE DUALITY Diffraction of Waves Si

59、ngle-slit diffraction Light is a wave The wave relationship between frequency and wavelength is true for light. c More evidence that light is a wave exists since it can be reflected, refracted and diffracted. When a traveling wave hits a hole (slit) that is approximately the size of the waves wavele

60、ngth, the wave “expands” as it goes through the hole. Direction of propagation Supplemental Double-slit diffraction When a wave is incident on two slits relatively close to each other, a diffraction pattern appears when the waves constructively and destructively interfere with each other. Comments a