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INTRODUCTORY INFORMATION
Chemistry: the study of matter and its changes Proust’s Law of Definite Proportions: any sample of a pure compound will have the same elemental composition by mass. DALTON Law of Multiple Proportions: if elements A and B form two different compounds, the ratio of the compounds’ mass ratios is a whole number or a simple fraction Atomic Theory of Matter: Elements are composed of tiny particles called atoms Atoms of the same element have the same mass and the same chemical properties Atoms combine in whole number ratios to form compounds Chemical reactions do not change the atoms, only the way they are combined ATOMS (^) Composed of: -Protons (p+) -Neutrons (n) -Electrons (e-) (^) Element defined by number of p+^ (z) (^) In a neutral atom, number of p+^ = number of e- (^) Mass number (A) = # p+^ + # n (^) Atoms of same element with different A are isotopes (^) Atomic mass units: 12 atomic mass units (u) is the mass of one atom of 12 C THE MOLE AND ITS MEASURES 1 mole = amount of substance that has as many entities as 12 grams of 12 C Avogadro’s Number = 6.022 * 10^23 = number of entities in 1 mole 6.022 * 10^23 u = 1 gram Molar mass of an element: mass of 1 mole of atoms in grams Molar mass of a compound = sum of molar masses of all individual atoms in the compound Molar Mass (M) o Used to measure moles of a substance in solution o M = mol solute / L solution In dilutions: M 1 V 1 = M 2 V 2 MICELLANEOUS MEASURES Density: Mass of sample / volume of sample Percent yield: Experimental mass of product / Theoretical mass of product
STOICHIOMETRY
“measuring elements” Must use a balanced chemical equation Balancing equations: 1.) Never change subscripts 2.) Use coefficients in front of chemicals to balance atoms that appear only once per side 3.) Use coefficients (fractions are OK) to balance atoms that appear more than once per side 4.) Multiply/divide to get the smallest whole number ratio Sometimes, an excess of one reactant is used o Limiting reactant: used up first. Reaction stops when limiting reactant in gone o Excess reactant: some remains after reaction stops o Hint: if you are given a way to find moles of all starting materials, it is probably a limiting reactant problem ATOMIC STRUCTURE THE e-^ IS CRITICAL IN CHEMISTRY Sharing of e-^ between atoms- chemical bonding Rearrangement of e-^ between atoms- chemical reactivity Unpaired e-^ - magnetism e-^ travel in a solid- conductivity CATHODE RAY EXPERIMENT (late 1800’s) (^) http://www.lightandmatter.com/ html_books/4em/ch01/figs/deflect.png (^) First evidence of e- (^) Cathode ray attracted to a (+) electrical field and deflected by a (-) field, showed that the particles had a (-) charge
http://acept.la.asu.edu/PiN/rdg/color/spectrum.gif o Gamma rays: high E, very toxic, produced by black hole collisions and during radioactive nuclear decay o X-rays: high E, toxic in high doses, produced when high E e-^ collide with metal target o UV and visible: caused by e-^ dropping to lower E levels o Infrared: emitted by vibrating chemical bonds o Microwaves: produced by circulating electrical field, causes molecular rotation o Radio waves: caused by oscillating electrical fields NIEL BOHR Explained why only four lines were observed in H emission spectrum e-^ orbits nucleus in circular path, only certain orbits with specific energies are allowed Electrical or thermal E can promote e-^ to higher E orbits Light is emitted when e-^ drop down in orbits E of light emitted corresponds only to the E gaps between the orbits that the e- travels Equation for energy of an e-^ in an H atom: E = -Rhc/n^2 where n is orbit number (principle quantum number as mentioned below) From above equation: ΔE = EE = Efinal – Einitial = -Rhc(1/nfinal^2 – 1/ninitial 2
Energy of an e-^ has the same magnitude as the E it takes to remove that e-^ from the atom (ionize) QUANTUM NUMBERS SCHRÖDINGER Described electron as a wave not a particle Created the wave function (ψ), which supports that the E of the e), which supports that the E of the e-^ is quantized Ψ^2 is related to the probability of finding the e-^ within a given region of space To solve the wave function, the three integer quantum numbers-n, , and m-are needed PRINCIPLE QUANTUM NUMBER (^) Principle (n) = 1,2,3,…, (^) Primary factor in determining energy of an e- (^) Defines size of an orbital- as n increases, so does the e-‘s average distance from the nucleus (^) Two or more e-^ may have the same n (^) n = number of subshells in a shell, n^2 = number of orbitals in a shell ANGULAR MOMENTUM QUANTUM NUMBER
Angular (l) = 0,1,2,3,…,n-
Determines subshell in which an e-^ resides Each number corresponds to a different orbital shape or orbital type Value of l Corresponding Subshell Label 0 s 1 p 2 d 3 f
Value of lalso specifies number of planar nodes in the orbital in any given
subshell MAGNETIC QUANTUM NUMBER
Magnetic (ml) = any integer between - land l
Related to the orientation in space of the orbitals within a subshell Number of m values for a given equals the number of orbitals within that
subshell = 2 l+ 1
PAULI EXCLUSION PRINCIPLE
Principle: no two e-^ in a single atom may have the same exact set of quantum numbers 4 th^ QN-Spin Quantum Number (ms) o Only permissible values are ½ and –½ o Therefore, only two e-^ can reside in a single orbital ELECTRON CONFIGURATION e-^ CONFIGURATION (^) Listing of e-^ populations in various subshells of an atom Example: Fluorine 1s^2 2s^2 2p^5 (^) Represents ground state- e-^ placement for lowest atom E (^) Orbitals are still present when empty (^) e-/e-^ repulsion can occur, giving orbitals of a given n different E (^) Subshells are filled with e-^ from lowest E to highest E (^) Diagonal rule is used as a guide to subshell E ordering http://www.explorelearning.com/ELContent/gizmos/ELScience_Deliverable/ ExplorationGuides/images/EL_MSCH_ElectronConfig1.gif o Some exceptions to diagonal rule
Main group (s & p blocks) elements tend to form ions in order to achieve noble gas configuration o Na ([Ne]3s^1 ) e-^ + Na+^ ([Ne]) o N ([He]2s^2 2p^1 ) + 3e-^ N3-^ ([Ne]) Transition metals (d block) form cations, but noble gas configuration is usually not achieved o Fe ([Ar]3d^6 4s^2 ) 2e-^ + Fe2+^ ([Ar]3d^6 ) IONIC COMPOUNDS Ionic compounds are overall electrically neutral compounds formed by the combination of anion and cation o Li
- (^) N3- (^) Li 3 N o Co 2+ (^) Cl- (^) CoCl 2 o Cr 4+ (^) O2- (^) CrO 2 Naming binary ionic compounds o Cation gets element name and comes first o Anion is element name ending in –ide and follows cation name o No numeric prefixes are used o Transition metal cation charges are indicated with a roman numeral o Examples: Li^3 N – lithium nitride, CrO^2 – chromium (IV) oxide PERIODIC TRENDS AND CHEMICAL PROPERTIES ATOMIC RADIUS Atomic radius (r): size of atom Going down a column, r increases o More filled e-^ shells o Larger amounts of e-/e-^ repulsion o Atom size swells Going across row, r decreases o Filled inner e-^ shells screen out the full attractive effect of the (+) nucleus o Going L to R, number of p+^ increases while the inner filled e-^ shells remain unchanged (thus screening effect does not change either) o Outermost e-^ then feel a greater attraction to nucleus and atomic radius decreases (^) Exception to trend: last column of d block elements are slightly larger than expected – filled d subshell and greater e-/e-^ repulsion
IONIC RADIUS
(^) Cation is smaller than its parent atom- fewer e-, less e-/e-^ repulsion (^) Anion is larger than its parent atom- more e-, more e-/e-^ repulsion (^) Isoelectronic cations have the same number of e- o (^) Example: Na+, Mg2+, Al3+ o (^) Follow atomic radius trend by parent atom IONIZATION ENERGY Ionization energy (IE): energy required to remove an e-^ from a free atom in the gas phase, measured in kJ/mol IE 1 represents first ionization energy, IE 2 represents second ionization energy o (^) Li (g) Li+^ (g) + e-^ IE 1 = 513 kJ/mol o (^) Li+^ (g) Li2+^ (g) + e-^ IE 2 = 7298 kJ/mol o (^) IE generally increases after each ionization- every time an atom loses an e-, the remaining e-^ are pulled in closer to the nucleus and are held in with a greater force Going down a column, IE 1 decreases o Outermost e-^ is farther away from nucleus, making it easier to remove o Explains increasing reactivity LiNaKRbCs Going across row, IE 1 increases o r decreases from L to R o outermost e-^ gets closer to nucleus and is harder to remove (^) Exception to trend: slightly easier to remove outermost e-^ from O than from N, as doing so will create a half filled valence 2p shell in O ELECTRON AFFINITY (^) e-^ affinity: E change that occurs when a neutral gas phase atom accepts an e- (^) X + e-^ X- o (^) If X- (^) is more stable than X, electron affinity will be (-), energy will be released when X-^ is formed o (^) If X- (^) is less stable than X, electron affinity will be (+), energy is required to form X- Halogens have the most negative electron affinity, as accepting an e-^ creates noble gas configuration Noble gasses have the highest positive electron affinity, as accepting an e-^ breaks noble gas configuration There is no clear trend for electron affinity ELECTRONEGATIVITY Electronegativity (X): the ability of an atom, when in a compound, to attract e-^ to itself Critical to types of chemical bonding, intermolecular forces, and physical properties Going down a column, X decreases. Going across a row, X increases. F has highest X = 4.0, Cs has lowest X = 0.
BOND ORDER
Bond Order (B.O.) = total # of bonds / # of connections Applies to one resonance structure at a time Can be used as a relative measure of bond length o Double bonds are shorter than single bonds and longer than triple bonds for the same set of atoms o The higher the B.O. for each connection, the shorter the bond Can be used as a relative measure of bond energy o Triple bonds are stronger than double bonds, which are stronger than single bonds between the same atoms o The higher the B.O. for each connection, the stronger the bond NAMING CHEMICAL COMPOUNDS NAMING MOLECULAR COMPOUNDS Non-metals only, not acids Name less electronegative atom first Name more electronegative atom second using –ide ending Use numeric prefixes to indicate how many of each atom Examples: H 2 O – dihydrogen monoxide, S 4 N 4 – tetrasulfur tertranitride NAMING IONIC COMPOUNDS Binary ionic compounds o Name metal first, then non-metal o d block element- indicate charge as Roman numeral o anion (non-metal) name, -ide ending Polyatomic ions o Charged groupings of non-metal atoms held together with covalent bonds o Do not break down further in aqueous soution o In compound name, place polyatomic ion name in its appropriate place (cation/anion) o Examples: CuSO 4 – copper (II) sulfate, Na 2 CO 3 – sodium carbonate, Ca(ClO 3 ) 2 – calcium chlorate o Common polyatomic ions (taken from La Duca R. (2006). Polyatomic ions. Acetate CH 3 COO-^ Ammonium NH 4 + Carbonate CO 3 2-^ Dichromate Cr 2 O 7 2- Chlorate ClO 3 -^ Hydroxide OH- Chromate CrO 4 2-^ Nitrate NO 3 - Cyanide CN-^ Permanganate MnO 4 - Cyanate CNO-^ Phosphate PO 4 3- Sulfate SO 4 2- o Other anions can be named with the following rules (ibid)
Removing or adding O atoms without changing the charge Adding an O atom to “ate” ion per…ate Losing an O atom from “ate” ion …ite Losing 2 O atoms from “ate” ion hypo…ite Adding an H+^ to anions to form other ions Adding an H+^ to an anion hydrogen (anion name) Adding 2H+^ to an anion dihydrogen (anion name) Substituting an S atom for an O atom without changing the charge: +S, -O thio(anion name) NAMING ACIDS (^) Acid can be recognized as any neutral compound whose only cations are H+ Parent anion ending Acid name -ide Hydro__ic acid -ate __ic acid -ite __ous acid MOLECULAR STRUCTURE VSEPR-VALENCE SHELL ELECTRON PAIR REPULSION (^) Theory: groups of e-^ on a central atom try to maximize the distance between themselves (^) Predicts molecular geometry of main group p-block compounds (^) One e-^ group is any of the following: a single bond, a double bond, a triple bond, a lone pair, a single lone electron (^) General shapes and bond angles e-^ groups 0 lone pairs (basis shape) 1 lone pair 2 lone pairs 3 lone pairs 2 Linear 180° - - - 3 Trigonal planar 120° Bent - - 4 Tetrahedral 109° Pyramidal Bent - 5 Bipyramidal 90°, 120°, 180° See-saw T-shaped Linear 6 Octahedral 90° Square Pyramidal Square Planar - MOLECULAR POLARITY POLARITY Polarity: the ability of a substance to respond to an applied electric field o Polar will respond to an electric field o Nonpolar will not respond to an electric field Polarity’s significance o Polarity has a large effect on solubility
o In molecules with two or more e-^ on the central atom, single bonds, σ only, are formed by the overlap of a hybridized orbital of the central atom and an orbital of a terminal atom o Multiple bonds consist of 1 σ bonds and one or more π bonds. The π bonds are formed by the overlap of unhybridized orbitals on two different atoms ORGANIC CHEMISTRY INTRO Out of 15mil known chemical compounds, 14.9mil are organic Because of a C base, many compounds can be made o C is small and makes good orbital overlap o C can make four bonds o C can link into long chains or rings o There is a 3-D geometry around C Organic compounds make up all living material Organic compounds are used to make medicines and polymers NAMING 1.) Find longest uninterrupted C chain parent name, consider functional groups (discussed below) 2.) Number the chain from the end closest to any substituents (non-Hydrogen groups) (Minimize sum of number positions of substituents and functional groups/ multiple bonds of alkenes/alkynes) 3.) State the position number of the substituent, name substituent as a prefix 4.) combine prefix and parent name ISOMERS Isomers have the same chemical formula but different structures True isomers have unique names Degree of Unsaturation (DOU) = (2+2(C)+N-H-X) / 2 = number of rings and/or π bonds possible in any isomer of a given formula Cis –trans isomers o Cis isomers have identical groups attached to each C of a multiple bond on the same side of the bond o Trans isomers have identical groups attached to each C of a multiple bond on opposite sides of the bond Regioselective reactions favor the production of one isomer over all others CHIRALITY Enantiomers: isomers with handedness (non-superimposable images) o Have same physical properties (except for rotation of plane polarized light) o Different enantiomers will react with other chiral molecules differently Chiral molecules o Have handedness
o Virtually all amino acids and sugars are chiral o A molecule must have four different things attached to a single C atom to be chiral (these C’s are stereocenters) o Number of stereoisomers possible = 2n, n = number of stereocenters The reactions in the following organic chemistry sections taken from La Duca R. (2006). Organic reactivity ALKANES Have C-C and C-H single bonds only General Formula: CnH2n+ Saturated hydrocarbons Name ends in -ane Relatively unreactive Reactions o Halogenation: Alkane + Halogen (light) Alkyl halide o Combustion: Alkane + O 2 CO 2 + H 2 O ALKENES Each has a C=C double bond General Formula: CnH2n Name ends in –ene, indicate number position of double bond in carbon chain More reactive than alkanes Reactions o Hydrogenation: Alkene + H 2 (Pt catalyst) Alkane o Hydrohalogenation: Alkene + HBr Alkyl Halide ALKYNES Each has a C≡C triple bond General Formula: CnH2n- Name ends in –yne, indicate number position of triple bond in carbon chain Similar reactivity to alkenes, slightly more reactive – more e
- (^) in triple bond Reactions o Hydrogenation: Alkyne + H 2 (Pt catalyst) alkene (cis) o Halogenation: Alkyne + X 2 alkene dihalide (trans) AROMATICS
Name ends in –one, indicate number of C of ketone group in carbon chain Cannot be oxidized Reduction: Ketone + H-^ secondary alcohol CARBOXYLIC ACIDS Name ends in –oic acid, C of carboxylic acid group is carbon-1 in carbon chain Reactions o Deprotonization: carboxylic acid + base metal carboxylate o Ester Synthesis: carboxylic acid + alcohol (strong acid catalyst) ester ESTERS Naming: split RCO 2 – portion and the –R’ portion, –R’ portion is named normally replacing ending with –yl. The acid part is named by replacing -oic ending of acid with –oate. Example: CH 3 CH 2 CO 2 CH 3 is named methyl propanoate Saponification: ester (base catalyst) carboxylic + alcohol AMINES Protonation: amine + acid alkylammonium salt Condensation: amine + carboxylic acid amide POLYMERS Polymers are built from monomers, smaller repeating unit of a polymer Polymers are used in plastics and other technological materials Bipolymers make up cellulose, proteins, and genetic material Polymerization reactions o Addition monomers add to each other with no stable byproducts Substitted polyalkanes via free radical initiator catalyst o Condensation Two different monomers interact Stable small molecule byproduct is formed Dicarboxylic acid + diamine polyamide Condensation of amino acids polypeptides proteins THERMOCHEMISTRY
THERMOCHEMISTRY
Study of heat changes during physical or chemical processes Thermal E: E associated with random motion of atoms and molecules Law of Conservation of Energy o “First law of thermodynamics” o States that total E in the Universe is constant o E can neither be created nor destroyed, just changed from one form to another HEAT Heat: transfer of thermal E between two objects at different temperatures System: the chemicals and their container Surroundings: everything else Universe (Ū): system + surroundings Exothermic reactions release heat to surroundings Endothermic reactions absorb heat from surroundings HEAT TRANSFER Heat transfer (q) Enthalpy (H): heat transfer in an open system (constant pressure system) Change in enthalpy: ΔE = EH = Hfinal - Hinitial (unit: kJ / mol) In an exothermic reaction: A B + heat HA > HB ΔE = EH = HB – HA < 0 In an endothermic reaction: A + heat B HB > HA ΔE = EH = HA – HB > 0 COMPUTING HEAT CHANGES Heat change (q): q = mcsΔE = ET o m = mass o cs = specific heat: amount of heat E required to raise the temperature of 1 g of substance by 1°C (unit: J / (g*°C)) o ΔE = ET = Final temperature – initial temperature Phase changes o There is no temperature change (ΔE = ET = 0) during phase change o All added heat E increases motion of molecules o Heat change in phase change: q = nΔE = EH n = number of moles of substance ΔE = EH is constant and unique for each phase change of each compound, i.e. ΔE = EHfusion (H 2 O) = 6.01 kJ/mol Fusion: solid to liquid, freezing: liquid to solid, vaporization: liquid to gas, condensation: gas to liquid, sublimination: solid to gas
