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Fundamentals, Photoelectirc Effect, Quantum Numbers.docx

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McMaster University
David Brock

Sept 11/12 Chemistry Fundamentals - Colours signify state on the periodic table - Only 3 elements liquid at room temp - Period – rows, group – columns - Chemistry: materials, molecules, biology, biochemistry - Carbon: Diamonds decompose into graphite (more stable) - 196 liquid nitrogen boiling point? Oxidation State & Oxidation Numbers o Actual charge of a monatomic ion  Cl- (-1), Mg2+ (+2) o Hypothetical charge of an atom in a molecule or polyatomic ion  Co2 (C = +4, O = -2)  SO4 ( S= +6, O = -2) th o Rules of assigning O.S. (O.N) – Table 3.2 pg 85 10 ed. o The further the elements are on the periodic table, the more set they are with their oxidation number o Oxidation states can vary increasingly as they move further in the periodic table - Group 1 metals always + 1, group 2 metals always +2 - Higher elements take priority in terms of assigning oxidation numbers - O is usually – 2, sum of ON = overall charge - F is always -1 - H is almost always +1 except in metal hydrides. - Moving up the period table in group 1 decreases the likelihood of it being +1, moving down the periodic table in the last group decreases the likelihood of it being -1 o If comparing two elements in the same group, give the pos charge to the element that is lower in the periodic table  Eg. KNa, K has the pos charge; ICl, Cl has the neg charge - O = -1 in peroxides - TI2BaCa2Cu3O10 Nomenclature - “ous” is for the lower oxidation state, “ic” is for the higher - Simple ions – recognizing ON o Fe(II), Fe 2+ vs Fe(III), Fe 3+ - Ionic compounds – Table 3-3 o NaCl sodium chloride - Binary molecular compounds – Table 3-4 Sept 11/12 o - Polyatomic ions – Table 3-5 - Oxoacids & Their Salts – Table 3-6; binary acids Mole / Mass - n = m/M - mass 1 H atom = 1.0079 amu - mass of 1 mol H atoms = 1.0079 g mol -1 23 -1 - 6.022 x 10 mol Representation of Structure - Ionic compounds: cations (M+) + anions (X-) --. Formula unit (MX) - Sodium chloride: NaCl - Pottasium sulfide: K S 2 - Magnesium fluoride: MgF 2 - Empirical forumula is the simplest atom ratio eg. CH O 2 - Molecular formula: actual atom ratio eg. C H O 2 4 2 - Structural formula: connectivity (drawing it out with all the lines haha) - Condensed structural formula: eg. CH COOH 3 - Line-angle stick formula – used in organic chem, connect things together and assume there’s a carbon at every connection - “ball and stick” molecular model – the 3D plastic model kits - Space filling – never use. - Benzene: o Empirical formula: CH o Molecular formula: C H 6 6 o - Isotopes have natural abundance eg. 16O= 99.76%, 18O = 0.2% - H2O exists in many forms because of multiple stable H and O isotopes 1 16 2 16 1 2 16 1 18 o Eg. H O2 H O, H2H O, H O 2 - H2O (l) is richer in heavier forms which condense more readily, especially at lower temps - Depletion of heavy water from snow at earth poles = greater when earth cooler - Water evaporates, goes up, lighter it us, further it’ll be carried and falls once it hits the poles - Compare oxygen 16 with oxygen 18 - Higher temps cause more evaporation cause water to move farther - Investigate isotopes in deep ice core to look at temps of the past years, see what the temp on earth was, compare O isotope changes, CO2 changes - Higher temp with more CO2 – global warming Sept 11/12 - Temperatures: 0K – absolute zero; 0C = 273 K - 14 C = 287 K, 15 C = 288 K - For Celsius, delta T btwn 14 & 15 is 1; for K, delta T btwn 287 & 288 is 1 - Extensive properties – depends on the amount of substance involved o Eg. M, V, heat capacity; heat – heat scales with amount of substance however, heat characterizes a process undergone by a substance – it is not a property of a substance - Intensive properties – independent of the amount of substance involved o Temp, density, specific heat capacity, Pressure o P is as intensive, not extensive, property (consider atmospheric pressure – a reading independent of how much outside air we “ measure”, similar idea to temp) o Eg. Density of a penny is the same throughout, same temp throughout a room - N = c x v, m = d x v - % by mass = mass of solute / mass of solution x 100 Essential Elements: Chemistry, Life, & Health (Chapter 8) Sept 18/12 - Atoms are mostly space, nucleus, electrons o Electrons are described by quantum mechanics, not traditional mechanics o Electrons behave like particles and waves o Their movement has associated changes in energy o Not at fixed distances / in fixed locations o Orbitals describe regions in space where electrons are likely to be found o Quantum numbers describe orbitals - Looking at how light interacts with atoms helps discover things about movement of electrons - High frequency = short wavelength, short frequency = high wavelength; together always = speed of light - Shorter the wavelength, higher the energy - Most of the sun’s emission spectrum is visible light - UV radiation associated with photolysis - Ozone & UV Exposure o 90% U B radiation from the sun is selectively absorbed by phytoloysis O3 in stratosphere, with peak at ~ 20km from earth’s surface o Lower O3 levels increase the transmittance of UVB radiation to earth  motreal protocol 1987 o O3 breaks apart at the ozone to create O2(g) + O(g) + heat o Ozone layer blocks out UV radiation o Biological impacts:  UVB radiation can ionize biological molecules (DNA, protein)  Chronic exposure to UVC rays increases chance of skin cancer, cataracts, genetic mutations Sept 11/12  Body`s response: produce melanin (dark pigment) to filter UV B radiation – melanin is like a natural sunscreen, selectively absorb UV radiation before it gets into your cells; chemical sunscreen  UV radiation interacts with adenosine (aromatic base in RNA/DNA) and tryptophan o Chemistry of sunscreen:  Propose alternative ways to decrease exposure to UV radiation  Use of sunscreen/cosmetics containing UV absorbing chemicals  Physical susnscreen – deflect or block sun’s rays  Chemical sunscreens absorb UV radiation, dissipate energy via heat instead of harming your cells  UVA 275/340 will absorb less effectively but broader spectrum coverage  UVB is better at absorbing one wavelength – narrow coverage but more effective at that one wavelength - Atomic Spectra o Absorption spectrum (absorbing energy) or emission spectrum (give off energy) o Burning gas, producing energy, promote electrons to higher energy levels o Discontinuous (line) spectra of atoms; few wavelengths  Don’t see every colour of the spectrum, only specific colours can be emitted  Not typical physical properties that you’d expect on the atomic scale - Current model of the atom o Experiments done during early 1900s proved that the classical model of the atom was insufficient - Quantum: Theory & Experiment o Max Planck proposed (1900): energy, like matter, is discontinuous (quantized) o Quantum (photon) of energy, E = hv where E = energy, v = frequency, h = Planck’s constant, 6.626 x 10^-34 J s o Idea used by Einstein to explain Hertz’s experiment The Photoelectric Effect – physical properties behind how solar panels work  Single wavelength of light strikes a metal surface to which a voltage is applied  If E > threshold energy (work function) of metal, e- are ejected with kinetic photon energy (KE)  Minimum threshold energy , specific amount, discrete amount all at one ti
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