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UNT CHEM 1415 - Exam 2 Study Guide
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CHEM 1415 1nd EditionExam # 2 Study Guide Lectures: 10 - 15Lecture 10 (September 23)Gases: Gaseous StoichiometryAir Pollutiono Criteria Pollutants CO, NO2, O3, SO2, Pb,o Primary Standards Pollutant standards intended on protecting our healtho Secondary Standards Pollutant standards intended on protecting environment and propertyo Photochemical reaction Light energy from the sun initiates chemical changes in air pollutantso Volatile organic chemicals VOCs  Key additional components needed for a photochemical reactionProperties of Gaseso Expand to fill volume of any containero Have much lower densities than solids or liquidso Have highly variable densities, depending on the conditionso Mix with one another readily and thoroughlyo Change volume dramatically with changing temperatureIdeal Gas LawPV =nRTo Universal gas constant – R = 0.08206 L atm mol^-1 K^-1PressureoP=FAoUnits 1 torr = 1 mm Hg 1 atm = 760 torr 1 atm = 101,325 Pa 760 torr = 101,325 PaCharles lawo Expressing temperature on the Kelvin scale makes the volume and temperature are directly proportionalBoyle’s lawo States that at constant temperature, pressure and volume are inverselyproportionalAvogadro’s lawo States that the volume of a gas is proportional to the number of molecules of gaspresentLecture 11 (September 25)Kinetic Molecular Theory  Dalton’s Law of Partial Pressureso The pressure of a mixture of gas is equal to the sum of the partial pressuresPtotal=PN2+PO2+PCO2+PAr+…Ptotal=nN2RTV+nO2RTV+nCO2RTV+nArRTV+…Ptotal=( nN2+nO2+nCO2+nAr)RTVxi=nintotal Kinetic Molecules Theory of Gases1. gas – made up of particles in constant motion2. particles are very small – occupy no volume3. particles move in straight lines until colliding with each other or the walls of the entrancea. collisions are elastic ≡ kinetic energy is conserved4. particles interact only by collidinga. no repulsions or attractions5. average kinetic energy α K temperature- P α1V (with T, n constant)o larger volume →longer distance for particles to travel → fewer collisions with the wall → lower pressure- V α T (with P, n constant) o increase temperature →increase the velocity of the particles → to keep pressure constant , volume must increase- V α n (with P, T constant) o because – no volume for the particles – no interaction between the particles→ only depends on number of particles Electromagnetic spectrumo Visible light is only a small portion Wavelengtho Distance between corresponding points on adjacent waves Amplitudeo Size or height of the wave Frequencyo Number of complete cycles of the wave passing a given point per second (Hz)c=2.99792458∗108m s−1c=λ∗vLecture 12 (September 30)Model of the Atom Bohr Model of the Atom:o Proposed the idea that electrons occupy stable orbits from which they can’t deviate without first absorbing or emitting energy in the form of light, however not completely correct Variables in the wave equation of quantum numbers: n, l, ml, mso n – Principle quantum number, row numbero l – secondary polynomial number, n-1oml - magnetic quantum number, orientation of the orbital, from +l to –ln Lmlms1 0 0 1s2 0 0 2s2 1 1 2p2 1 0 2p2 1 -1 2p3 0 0 3s3 1 1 3p3 1 0 3p3 1 -1 3p3 2 2 3d3 2 1 3d3 2 0 3d3 2 -1 3d3 2 -2 3d Pauli Exclusion Principle:o No two solutions in the same atom can have the same set of quantum numbersGround StateH1 s1He1 s2Li1 s22 s1Be1 s22 s2B1 s22 s22 p1C1 s22 s22 p2N1 s22 s22 p3O1 s22 s22 p4F1 s22 s22 p5Ne1 s22 s22 p6Na1 s22 s22 p63 s1Mg1 s22 s22 p63 s2Lecture 13 (October 02)Chemical Bonding, Lewis Dot Structures Polarity – nature of electrical charges on the surfaceso Na2+ isn’t found in nature because the energy needed to remove the second electron from the core electron is quite large Formation of anionso Energy is released when anions are formedo Amount of energy released when atoms acquire additional electrons tends to increase from left to right across the periodic tableo Ionic radius increases for ions as you move down a group Covalent Bondso Based on the sharing of pairs of electrons between two atomso Bond energy – energy released when isolated atoms form a covalent bondo Bond length – distance between the nuclei of the bonded atoms Octet rule: an atom will form covalent bonds to achieve a complement of eight valence electrons. The exception is hydrogeno Lewis Dot – conveniently depicts the octet rule with a doto The elements in the second period have the following lewis symbols Lewis Dot Structure o Shows how electrons are shared in a moleculeo By sharing the electron from each atom, two hydrogen atoms can form a chemical bondo Group 1, all have one valence electrono Group 2, all have 2 valence electronso Group 13, all have 3 valence electronso Group 14, all have 4 valence electronso Group 15, all have 5 valence electronso Group 16, all have 6 valence electronso Group 17, all have 7 valence electronso Group 18, all except He have 8 valence electronso Bonding pair – a pair of electrons shared by two atomso Lone pairs – the other paired electrons that are associated with a single atom, non bonding electrons Fluorine molecule has one bonding pair and six lone pairso Double bond – two pairs of electrons are sharedo Triple bond – three pairs of electrons Electronegativity o Attraction of an atom for the shared electrons in a covalent bondo The higher the electronegativity value, the more likely an element is to attract extra electron density when it forms chemical compoundso Fluorine is the most electronegative element, value = 4.0o Molecules form a covalent bond and one atom is slightly more positive while the other is slightly more negative, this creates an electric fieldo Dipole – two points of positive and negative charge in a moleculeo Polar bond –the bond between two atoms that have a dipoleo The greater the difference in electromagnetivity, the more polar the bondo If the electronegativity difference exceeds 2.0, the bond is classified as ionic How to study Lewis Structures:o Step 1: count the total number of valence electrons in the molecule or iono Step 2: draw the skeletal structure of the moleculeo Step 3: place single bonds between all connected atoms in the structure by drawing lines between themo Step 4: place the remaining valence electrons not accounted for in step 3 on individual atoms until the octet


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