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Chemistry 1- CHEM 1331 Week 2 Notes Chapter 1-2

by: Alexis Clowtis

Chemistry 1- CHEM 1331 Week 2 Notes Chapter 1-2 CHEM 1331

Marketplace > University of Houston > Chemistry > CHEM 1331 > Chemistry 1 CHEM 1331 Week 2 Notes Chapter 1 2
Alexis Clowtis
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These notes cover the second week of class, beginning with the scientific method and going through wave-particle duality. This includes tophat questions, sample problems, and some elaboration from ...
Fundamentals of chemistry
Thomas Teets
Class Notes
Chemistry, scientific method, atomic structure, wavelength, frequency, photon, electron, neutron, radiation, quantum theory
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This 11 page Class Notes was uploaded by Alexis Clowtis on Wednesday February 3, 2016. The Class Notes belongs to CHEM 1331 at University of Houston taught by Thomas Teets in Spring 2016. Since its upload, it has received 61 views. For similar materials see Fundamentals of chemistry in Chemistry at University of Houston.


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Date Created: 02/03/16
Chemistry 1331- 12pm MWF SEC 100 Professor Thomas Teets The Scientific Method 01/25/2016 Observation: something you sense or measure  Qualitative- what happens, what something looks like  Measurement, numerical value + a unit Hypothesis: possible explanation for what you’ve just observed; usually based on limited or flawed information Experiment: designed to carefully test hypothesis Law: explains what happens Theory: explains why it happens (stands the test of time)  A lot more advanced and developed than a hypothesis Early Chemical History The Greeks:  Tried to explain chemical changes  Proposed 4 fundamental substances: Earth, Fire, Water, Air  First to propose atoms as fundamental building blocks of matter as fundamental particles The Alchemists:  “pseudoscience”  Spanned ~2000 years  Tried to change base metals (ex. Lead) to gold Robert Boyle:  First “chemist”  Quantitative measurements on gases o Measured relationship between pressure and volume of air  Proposed the concept of elements Greek concept of elements died out Joseph Priestly  Discovered oxygen  Careful studies of chemical reactions Chemistry 1331- 12pm MWF SEC 100 Professor Thomas Teets Three Laws, One Theory 1. Mass conservation- Antoine Lavosier a. In a chemical reaction, the mass of what you start with (reactants) is equal to the mass of what forms (products) b. Matter is neither created nor destroyed in a chemical reaction 2. Definite Composition- Joseph Proust a. A given compound always contain the same proportion of elements by mass, regardless of the source i. Ex. 44g of Carbon dioxide contains 12g of carbon and 32 g of oxygen b. Every compound has a constant mass % i. ???????????????? % = ???????????????? ???????? ????????????????????????????????100 ???????????????? ???????? ???????????????????????????????? ii. Example: CO :2mass percent of oxygen= 32g/44g x 100= 73% mass percent of carbon= 12g/44g x 100= 27% (Should add to equal 100%) 73% oxygen by mass, 27% carbon by mass in ANY carbon dioxide “sample” iii. Mass percent of an element is 100% iv. Example: Pyrite= iron+sulfur 50.0g of pyrite has 26.7g sulfur, what is the mass % of iron in pyrite? Mass % Fe: 23.3g/50.0g x 100= 46.6% ???????????????? ???????? ???????????????????????????? v. ???????????????? ???????????????????????????????? = ???????????????? ???????? ????????????????????????????????(just mass % without multiplying by 100) 3. Multiple Proportions a. If one gram of Element A combines with Element X to form 2 different compounds, the masses of X that combine with A are small, whole- number rations of each other i. Ex. 2:1, 3:1. 3:2 ii. Ex. Ferrous oxide and rust are 2 compounds with iron and oxygen only Ferrous oxide= (mass oxygen)/(mass iron)= 22.27/77.73 = 0.2865 Rust: (mass oxygen)/(mass iron) = 30.06/69.44 = 0.4329 .4329/.2865= 1.5  3:2 *Mass ratios can be used as conversion factors* Chemistry 1331- 12pm MWF SEC 100 Professor Thomas Teets The Unifying Theory Dalton’s Atomic Theory 1. Substances are composed of tiny particles called atoms which cannot be decomposed further 2. Atoms cannot be converted into different atoms-elements cannot be interconverted 3. Atoms of a given element have the same mass and other properties; distinct from other elements 4. Chemical compounds are formed when atoms of different elements combine in a specific ratio; reactions involve reorganization of the atoms Guy-Lussac’s Observations: at equal temperature and pressure, gases combine in chemical reactions in fixed, whole number ratios; 2 volumes hydrogen + 1 volume oxygen2 volumes water vapor Avogadro’s interpretation: at the same temperature and pressure, equal volumes of different gases have the same number of particles 2 molecules hydrogen + 1 molecules oxygen2 molecules water Key: ∴ = Therefore Chemistry 1331- 12pm MWF SEC 100 Professor Thomas Teets Sections 1-6—1-7 01/27/2016 The Electron: Cathode Ray Experiments- J.J. Thompson Thompson studied electrical discharges in partially evacuated tubes called cathode-ray tubes; found when high voltage was applied to the tube, a ray he called the cathode ray because it emanated from the negative electrode or cathode, was produced Key observations:  Cathode rays are repelled by negative pole of an electric field  “electrons” could be produced from many different materials (doesn’t matter what you used)  Concluded all atoms have these electrons  Determined charge to mass ratio o Couldn’t get absolute charge or mass but could get the ratio of the 2 The Electron: Oil Drop Experiment- Miliken Key Observations:  Falling negatively charged oil drops stopped by an electric field o Induce electric field and charged particles  Charges on oil drops occur in regular intervals  Determined the mass and charge of an electron o Using this information and the stuff from the cathode ray o Didn’t really add information about structure of atom just reaffirmed existence of the electron Early Picture of the Atom Thomson--Plumb-pudding model: atoms consist of electrons held in place by a diffuse cloud of positive charge; electrons are randomly embedded in this positive charge (no set location for electrons) Electrons are floating around with positive charges (not clumped together) like raisin plum pudding The Nucleus: Gold Foil Experiment—Rutherford (The Nuclear atom)  Expected outcome: alpha (α) particles would mostly pass straight through (if plumb pudding model was right) or be slightly deflected  Actual outcome: most particles went straight through but some were deflected at very large angles or reflected completely (came straight back at source)  Explanation: the positive charge and most of the atom’s mass is in a very small area, called “nucleus” ( nuclear picture of atom) Chemistry 1331- 12pm MWF SEC 100 Professor Thomas Teets (image from Professor’s slides) *Size relationship: golf ball= nucleus, football field=atom Summary of Subatomic Particles *Nucleus also contains neutrons* Chemistry 1331- 12pm MWF SEC 100 Professor Thomas Teets Atomic Symbols The number of protons in the nucleus distinguishes one element from another (defines what atom/element you’re talking about) Atomic Symbol: X: Atomic Symbol= 1 or 2 letter abbreviation for element, first letter is capitalized (know symbol-name for first 36 elements) A: Mass Number= number of protons (p+) + number of neutrons (nº) Z: Atomic Number= number of protons (p+) in the nucleus All atoms of an element are not always the same, made of different isotopes usually Isotopes (mess with neutrons)  Definition: atoms of a given element that differ in the number of NEUTRONS (and hence the mass is different) DALTON WAS WRONG!  Properties: physical and chemical properties for a given element are nearly identical (generally going to react the exact same)  Examples: o 1????  1 proton, 0 neutrons o 2???? 1 proton, 1 neutron all 3 exist, only difference is number of nºs 3 o 1???? 1 proton, 2 neutrons Sample Problems: 1) Determine the number of protons, electrons, and neutrons in the two most abundant isotopes of palladium. 2) A fictitious element wit symbol Q has 34 protons and 43 neutrons in the nucleus. Write the proper atomic symbol for this element. 77???? 34 Chemistry 1331- 12pm MWF SEC 100 Professor Thomas Teets Formation of Ions  Neutral atoms: must contain equal numbers of protons and electrons to balance charge  Forming Ions: o Removing or adding electrons o Can NEVER add or remove protons to make that ion because that would change the identity of the atom itself (just mess with the cloud) o Add 1 electron for each negative charge, subtract 1 electron for each positive charge  Examples: How many protons, neutrons, and electrons are in the following ions: Using the periodic table to find the number of the protons Note: Z (Atomic number) is usually left out of symbol 12 12 6???? = C because the 6 is redundant with the C Determine which 2+ ion has the same number of electrons as Br . -- Br : protons= 35 electrons= 36 X 2+: protons=38  electrons=36 Sr 2+ Chemistry 1331- 12pm MWF SEC 100 Professor Thomas Teets 207 2+ Imagine that a Pb ion loses two protons and two neutrons (an alpha particle) from the nucleus. Give the atomic symbol for the resulting atom. 20Pb loses 2 protons and 2 neutrons  P+ =82 p+ =80 203  nº=207-82=125  nº =123 neutral 80???????? (80+123=203)  e- = 80 e-=80 (mercury) no net charge Chemistry 1331- 12pm MWF SEC 100 Professor Thomas Teets Chapter 2 1/29/2016 Quantum Theory Electromagnetic wave (“radiation”): energy propagated through space by electric and magnetic fields  Blue is electric, red is magnetic; perpendicular to each other  Oscillate intensity as they travel, not constant intensity  Examples: visible light, x-rays, radio waves, microwave Properties of a Wave Frequency (ν= “nu”): number of cycles per second (number of times it oscillates in 1 second) Units: Hz (1/s) Wavelength (λ): distance between corresponding points on a wave Amplitude (A): height of the crest- intensity Comparing Wavelengths/Frequencies (image from Professor’s notes with edits) Chemistry 1331- 12pm MWF SEC 100 Professor Thomas Teets Relationship between wavelength and frequency The wavelength is proportionate to the inverse of the frequency 1 ???? ???? ∝ ???? ???? = ???? ????λ = ???? ; C= speed of light in a vacuum, given on our periodic table C= 3.00x10 m/s Sample Problem 1. What is the frequency of 600.0 nm light, which is orange in color? νλ=C 8 ???? = ???? = 3.00????10 ????/???? = 5.000????10 ???????? = 500.0???????????? ???? 600.0????10 ????9 Quantization of Energy Blackbody radiation:  Concept: a solid heated to very high temperatures (around 1000K) emits visible light  Problem: Classical physics says that matter can absorb or emit any quantity of energy-fails to explain the wavelength/intensity relationship of blackbody radiation  Solution: Max Planck- Energy from electromagnetic radiation is “quantized” in whole-number multiples of h (planck’s constant) times frequency(ν) o ∆???? = ????ℎν h=6.626x10 -34Js n= integer (1,2,3,4, etc.) Chemistry 1331- 12pm MWF SEC 100 Professor Thomas Teets Photoelectric effect- Albert Einstein  Concept: if light strikes a metal surface, it ejects electrons  Problem: the light must have a minimum “threshold” frequency and below this frequency, nothing happens, no electrons are ejected, regardless of the intensity of the light  Solution: light consists of particles called photons and the energy of a photon is 1 2 ????????ℎ????????????????= ℎν K???????????????????????????????????? ????2 = ℎν − ℎ???? whe????e ν is toe threshold frequency and ν is the photon frequency E omin energy to remove e- (From professor’s notes) 2 De Broglie Wavelength- Einstein E=mc ???? ℎ???? ℎ ???? ????ℎ???????????????? = ????2 = ???? 2= ???????? ℎ ∴ For matter: ???? =???????? where v=velocity Wave-Particle duality “dual nature of light”  Matter and energy both have dual particulate and wave properties  Electrons exhibit wave-like behavior  Diffraction= scattering of light by a regular army of points or lines  Electrons are diffracted by crystals Sample Problems: 1) Commonly available red laser pointers have a wavelength of 635 nm. What is the energy of a 635‐nm photon? E=hc/λ 8 (6.626????10 −34????????)(3.00????10 ???? ) ???? −19 ????????ℎ???????????????? = 6.35????10 ????7 = 3.13????10 ???? TopHat: The work function is the minimum energy required to emit an electron from a metal surface. If the work function of rhodium is 7.98 x 10–19 J, which of these wavelengths of light will eject an electron from rhodium? (A) 225 nm (B) 325 nm (C) 175 nm (D) Both A and C −34 3.00????10 ???? 7.98x10 -19J=(6.626????10 ????????)( ???? )= 249 ???????? Ephotonwork function (Eo) ???? Ephotonhc/λ > Eo λ=hc/E so anything lower than 249 nm will eject electron


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