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PCAT: General Chemistry
isotopes - ANS an element that differs in mass numbers and neutrons but has the same number of protons (atomic number) Quantum theory - ANS developed by Max Planck proposing that E emitted as electromagnetic radiation from matter comes in discrete bundles called quanta. E of a quantum from equation E=hf (h=Planck's constant f=frequency of radiation) Bohr Model - ANS electron can exist only in certain fixed-energy states. E of an electron is quantized. smaller the radius, the lower the E state of the electron. this model is used to explain atomic emission spectrum and atomic absorption spectrum of Hydrogen Heisenberg uncertainty principle - ANS it is impossible to simultaneously determine the momentum and position of an electron four quanta numbers - ANS n=size l=shape ml=orientation of the orbital ms= spin principal quantum number (n) - ANS represents the shell where an electron is present in an atom. corresponds with that element's period in the periodic table. diff in E between adjacent shells decreases as the distance from the nucleus inc azimuthal (angular momentum) quantum number (l) - ANS tells the shape of orbitals and subshells. subshells include 0,1,2,3 corresponds to s,p,d,f subshells. the max number of electrons that can exist within a subshell is 4l+2. greater value of l, the greater the E of the subshell
magnetic quantum number (ml) - ANS describes orientation of the orbital in space. specifies the particular orbital within a subshell where an electron is highly likely to be found at a given point in time s subshell: 0 p subshell: -1,0, d subshell: -2,-1,0,1, f subshell: -3,-2,-1,0,1,2, spin quantum number (ms) - ANS 2 spin orientations are +(1/2) and -(1/2) whenever 2 electrons are in the same orbital they must have opposite spins bronsted lowry acid and base - ANS acid- species that donates protons base- species that accepts protons lewis acid and base - ANS acid- electron pair acceptor base- electron pair donor conjugate acid - ANS forms when a base gains a proton conjugate base - ANS forms when an acid loses a proton the weaker the acid, the _____ the ka (acid dissociation constant) - ANS smaller the weaker the base, the ______ the kb (base dissociation constant) - ANS smaller T/F: the larger the ka (the stronger the acid), the smaller the conjugate's kb (weaker the base) - ANS true
- noble gases have electron affinities on the order of zero bc they already possess full shells and can't readily accept electrons electronegativity - ANS - measure of the attraction an atom has for electrons in a chem bond
- greater an electron's electroneg, greater its attraction for bonding e-
- electroneg related to effective nuclear charge. larger effective nuclear charge, stronger pull the nucleus has on e-
- left to right of period= inc
- top to bottom group=dec ionic bonding - ANS - an e- from an atom with a smaller ionization E is transferred to an atom with greater e- affinity and resulting ions held together by electrostatic forces
- high MP and BP bc of electrostatic forces between ions
- conduct electricity in liquid and aq states but not solid state covalent bonding - ANS e- pair shared between 2 atoms polar covalent bond - ANS - bond is partially covalent and partially ionic
- occurs between atoms with small diff in electroneg
- bonding e- pair is not shared equally but is pulled more toward the element with higher electroneg
- higher electroneg element=partial negative charge
- lower electroneg element=partial positive charge bond length - ANS avg distance between 2 nuclei of the atoms involved in the bond what is the order of bond length from shortest to longest? - ANS triple bond, double bond, single bond. as # of shared e- pair increases, 2 atoms are pulled closer together leading to a dec in bond length
bond energy - ANS strength of a bond inc as the number of shared e- pairs inc formal charge - ANS formal charge= number of valence electrons- (# of sticks+#of dots) polar molecule - ANS polar covalent molec that has separation of positive and negative charges. dipole moment is a vector quantity nonpolar covalent bonding - ANS occurs between atoms that have same electronegativities. bonding e- pair is shared equally. ex: diatomic molec BrINClHOF valence shell electron-pair repulsion (VSEPR) - ANS uses Lewis structures to predict molec geometry of covalently bonded molec. 3 D arrangement of atoms surrounding central atom is determined by the repulsion between the bonding and nonbonding e- pairs in the valence shell of central atom. they want to be as far apart as possible, minimizing repulsion linear - ANS 2 electron pairs, 0 nonbonding pairs, 180 trigonal planar - ANS 3 e- pairs, 0 nonbonding pairs, 120 tetrahedral - ANS 4 e- pairs, 0 nonbonding pairs, 109. trigonal pyridmidal - ANS 4 e- pair, 1 nonbonding pairs, 107 bent - ANS 4 e- pair, 2 nonbonding pair, 104. trigonal bipyrimidal - ANS 5 e- pairs, 0 nonbonding pairs, 90,120,
orders of reaction - ANS exponents in a rate law. they are equal to the stoichiometric coefficients of the rate-determining step overall order of a reaction - ANS sum of the exponents of the orders of reaction zero order reactions - ANS has a constant rate, which is independent of the reactants' []. in medication, the amount of drug administered/eliminated each hour. first order reactions - ANS rate proportional to the concentration of 1 reactant. units s^-1. classic ex is radioactive decay. in medication, first order rxn is the % of drug administered/eliminated per unit time remains constant (amount of drug administered/eliminated is proportional to the amount of drug remaining) second order reactions - ANS rate proportional to the product of the [] of 2 reactants or to the square of the [] of a single reactant. units are M^-1 s^- Do reaction rates depend on temperature? - ANS yes. rxn rates inc with inc temp and vice versa activation E or E barrier - ANS minimum E of collisions necessary for a rxn to take place transition state - ANS when molec collide with sufficient E in which the old bonds are weakened and new bonds are beginning to form. has greater E than either the reactants or the products. do not have a finite lifetime enthalpy change - ANS diff between the potential energy of the products and the P.E. of the reactants activation E of forward rxn - ANS diff in potential E between activated complex and reactants in activation E
activation E of reverse rxn - ANS diff in potential E between activated complex and the products exothermic rxn - ANS when the potential E of the products is less than the P.E. of the reactants. enthalpy change is negative endothermic - ANS when the potential E of the products is greater than the P.E. of the reactants. enthalpy change is positive what factors affect reaction rate? - ANS depends on the individ species undergoing rxn and on the rxn environ.
- reaction [] inc [], inc rxn rate
- inc temp, inc rxn rate and vice cersa
- medium. faster rate of rxn in aqueous soln
- catalysts (lower activation E, not consumed) catalyst - ANS substances that inc rxn rate without being consumed by lowering activation E. E barrier for catalyzed rxn is much lower than E barrier for uncatalyzed rxn. rates of both forward and reverse rxn inc by catalyst. melting point periodic trend - ANS it is determined by the amount of E required to break or loosen IMF forces between the molec of an element. inc toward middle of period and then drop off. in second period, carbon as the highest MP. elements at the end of period have low MP T/F: water and alcohols are electrolytes - ANS False, they are not electrolytes. primary structure of proteins - ANS linear sequence of covalently linked amino acids. chain of linked amino acids how much does BP increase with molecular weight for each additional carbon? - ANS about 30 C
DNA polymerase - ANS reads parent DNA strand in 3'->5' direction and makes complementary, antiparallel daughter strand in the 5'->3' direction leading strand - ANS one daughter strand that is continually synthesized lagging strand - ANS other daughter strand that is synthesized discontinuously resulting in Okazaki fragments which is joined together by DNA ligase redundancy - ANS term to describe the genetic code bc most amino acids have more than one codon coding for them RNA structure - ANS sugar is ribose, contains uracil instead of thymine, and is single-stranded. can be found in the nucleus and cytoplasm what is the first step of transcription? - ANS RNA polymerase binds to DNA at a promoter region (TATA box in humans) what happens during post-transcriptional process of mRNA? - ANS introns (sequences not needed to make proteins) are spliced out leaving exons behind. guanine cap and poly-A tail added to ends of new molec to provide protection from enzyme degradation once the RNA leaves the nucleus ribosomes - ANS where translation takes place
- composed of 2 subunits (small and large)
- have 3 binding sites for tRNA (A,P,E site) what are the 3 ribosomal binding sites for tRNA? - ANS - A site: binds to the tRNA complex and transferred to P
- P site: tRNA contributes its amino acid to the growing polypeptide chain
- E site: tRNA is released after giving up its amino acid
Why are ribosomes targeted when making antibiotics? - ANS hum ANS and bacteria have diff types of subunits that make up their ribosomes. Antibiotic can target specific bacteria ribosome leaving human cells unharmed proteins - ANS some roles of proteins include providing structure, regulating body metabolism via hormonal control, and serve as catalysts (enzymes). composed mostly of C,H,O,N and can contain P and S amino acids - ANS contain an acidic amine group and a basic carboxyl group attached to a single carbon atom (alpha carbon atom). other 2 substituents are usually a H atom and an R group Is the alpha carbon on an amino acid a chiral center? - ANS yes except for glycine bc it has a H as its R group zwitterions - ANS neutral form of an amino acid that has both positive and negative charges amphoteric - ANS can act as either an acid or base. amino acids are amphoteric
- amino acids are fully protonated in acidic soln
- ...fully deprotonated in basic soln 2 dissociation constants when amino acids are protonated - ANS kal and ka 2 dissociation constants when amino acids are deprotonated - ANS kbl and kb isoelectric point (PI) or isoelectric pH - ANS intermediate pH at which amino acids is neutral and exists as a zwitterion. lies between pKal and pKa
what resonance structure is the true structure for an amino acid? - ANS the one with a partial C-N double bond bc the rotate about that bond is restricted primary protein structure - ANS chain, sequence of amino acids listed from N-terminus to C-terminus linked by covalent bonds secondary protein structure - ANS structure governed by H bond interactions within and between peptide bonds. ex: alpha helix and beta pleated sheets alpha helix - ANS rod-like structure that coils clockwise about a central axis. stabilized by H bonds between carbonyl oxygen atoms and amine H atoms 4 residues away. ex: keratin beta-pleated sheets - ANS peptide chains lie alongside each other in rows (rippled or pleated shape). held together by H bonds between carbonyl oxygen atoms on 1 peptide chain and amine H atoms on another. tertiary protein structure - ANS 3D shape of protein determined by hydrophilic and hydrophobic interactions between R groups of amino acids that are far apart on the chain and by the distribution of disulfide bonds. 2 classifications: fibrous proteins and globular proteins disulfide bond - ANS 2 cysteine molec became oxidized to form cystine. create loops in protein chain fibrous proteins - ANS ex: collagen sheets or long strands globular proteins - ANS ex: myoglobin spherical in shape
conjugated proteins - ANS molec with prothetic group attached meaning at least 1 portion of their structure is not made from protein (can be organic molec or metal ions). ex: lipoproteins, glycoproteins, nucleoproteins denaturation - ANS proteins lose their 3D structure and revert back to random-coil state. caused by detergent or changes in pH, temp, or solute [] lipids - ANS - characterized by insolubility in water and solubility in non polar organic solvents
- play roles in cell structure, signaling (cofactors, hormones, and intracellular messengers), and energy storage
- store the most E per unit weight of any molec in a human body
- all lipids have fatty acid tail amphipathic - ANS having hydrophilic and hydrophobic regions. ex: phospholipids are amphipathic saturated fatty acid tails - ANS have only single bonds. more stable and form solids at room temp unsaturated fatty acid tails - ANS have 1+ double bonds that create kinks in the fatty acid chains. tend to be liquid at room temp. most are cis configuration glycerophospholipids - ANS type of phospholipid that contains glycerol backbone. head groups can be +,-, or neutral which dictates its role in cell recognition, signaling, binding. important in membrane synthesis sphingolipids - ANS have sphingolipids or sphingoid backbone and have long, non polar fatty acid tails and polar head groups. ex: antigen on the surface of RBC that form basis of ABO blood type waxes - ANS esters of long chain fatty acids with long chain alcohols. protect against environ. help prevent dehydration and provide lubrication
water soluble vitamin - ANS excreted through urine lipid soluble vitamin - ANS can accumulate in stored fats. vitamins A,D,E,and K triglycerols - ANS used for energy storage. lightweight and E-rich. made of 3 fatty acids to glycerol why are triglycerols ideal for E storage? - ANS - C atom of fatty acid more reduced than those of sugars (oxidation gives 2x as much E per gram of carb)
- they are hydrophobic and do not draw in water dec their weight saponification - ANS hydrolysis of triglycerides by using a strong ace that makes soap binding energy - ANS amount of E required to break up a given nucleus into its constituent protons and neutrons mass defect - ANS diff in the larger mass for the constituent protons and neutrons of original nucleus in nuclear rxn radioactivity - ANS when the nucleus of an atom is unstable, it can spontaneously emit particles or electromag radiation how are nuclear rxns diff from chem reactions? - ANS nuclear: elements or isotopes are changed from one to another, large amounts of E involved, proton neutrons or e- involved chemical: atoms rearranged, small amount of E involved, only e- affected in orbital of atom involved what element has the most stable atom? - ANS iron bc the binding E per nucleon peaks here
how does fission nuclear reaction work? - ANS large, heavy atom splits to form smaller, more stable nuclei. by bombarding large unstable nuclei with neutrons, it can power commercial nuclear electric- generating plants alpha decay - ANS a type of radioactive decay. emission of an alpha particle. alpha particle very massive. daughter's atomic number will be 2 less than parent's atomic number and daughter's mass number will be 4 less than the parent's mass number what 2 nuclear reactions are the only radioactive decay process during which the mass number changes? - ANS alpha decay and fission beta decay - ANS emission of either a beta- (electron) or b+ (positron) from the nucleus positron - ANS similar to an e- (minimal mass) but has a positive charge beta - decay - ANS neutron is consumed and a proton takes its place. parent's mass number is unchanged and parent's atomic number is inc by 1 beta + decay - ANS proton is consumed and neutron takes its place. parent's mass number is unchanged and parent's atomic number is decreased by 1 gamma decay - ANS emission of a gamma particle which are high-E photons. it is a way for the nucleus to shed excess E by lowering the E of the emitting (parent) nucleus without changing mass # or atomic # electron capture - ANS capture of an inner e- that combines with a photon to form a neutron. atomic # now 1 less than the original but mass # still the same
