PCAT General Chemistry Exam Review: Key Topics and Concepts, Exams of Chemistry

Download PCAT General Chemistry Exam Review: Key Topics and Concepts and more Exams Chemistry in PDF only on Docsity! PCAT General Chemistry exam review questions and answers isotopes - an element that differs in mass numbers and neutrons but has the same number of protons (atomic number) Quantum theory - 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 - 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 - it is impossible to simultaneously determine the momentum and position of an electron four quanta numbers - n=size l=shape ml=orientation of the orbital ms= spin PCAT General Chemistry exam review questions and answers principal quantum number (n) - 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) - 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) - 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: -1,0,1 d subshell: -2,-1,0,1,2 f subshell: -3,-2,-1,0,1,2,3 spin quantum number (ms) - 2 spin orientations are +(1/2) and -(1/2) whenever 2 electrons are in the same orbital they must have opposite spins PCAT General Chemistry exam review questions and answers - left to right of period= inc - top to bottom group=dec - second ionization E is always greater than 1st ionization E electron affinity - - E change that occurs when e- is added to gaseous atom and represents ease when an atom can accept an e- - left to right of period= inc - top to bottom group=dec - noble gases have electron affinities on the order of zero bc they already possess full shells and can't readily accept electrons electronegativity - - 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 PCAT General Chemistry exam review questions and answers ionic bonding - - 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 - e- pair shared between 2 atoms polar covalent bond - - 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 - avg distance between 2 nuclei of the atoms involved in the bond what is the order of bond length from shortest to longest? - 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 PCAT General Chemistry exam review questions and answers bond energy - strength of a bond inc as the number of shared e- pairs inc formal charge - formal charge= number of valence electrons- (# of sticks+#of dots) polar molecule - polar covalent molec that has separation of positive and negative charges. dipole moment is a vector quantity nonpolar covalent bonding - occurs between atoms that have same electronegativities. bonding e- pair is shared equally. ex: diatomic molec BrINClHOF valence shell electron-pair repulsion (VSEPR) - 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 - 2 electron pairs, 0 nonbonding pairs, 180 PCAT General Chemistry exam review questions and answers rate-determining step - slowest step in a proposed mechanism bc the overall rxn cannot proceed faster than this step units of rate - units of moles per liter per second or molarity per second orders of reaction - exponents in a rate law. they are equal to the stoichiometric coefficients of the rate-determining step overall order of a reaction - sum of the exponents of the orders of reaction zero order reactions - has a constant rate, which is independent of the reactants' []. in medication, the amount of drug administered/eliminated each hour. first order reactions - 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 - 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^-1 PCAT General Chemistry exam review questions and answers Do reaction rates depend on temperature? - yes. rxn rates inc with inc temp and vice versa activation E or E barrier - minimum E of collisions necessary for a rxn to take place transition state - 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 - diff between the potential energy of the products and the P.E. of the reactants activation E of forward rxn - diff in potential E between activated complex and reactants in activation E activation E of reverse rxn - diff in potential E between activated complex and the products PCAT General Chemistry exam review questions and answers exothermic rxn - when the potential E of the products is less than the P.E. of the reactants. enthalpy change is negative endothermic - 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? - 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 - 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 - 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 PCAT General Chemistry exam review questions and answers leading strand - one daughter strand that is continually synthesized lagging strand - other daughter strand that is synthesized discontinuously resulting in Okazaki fragments which is joined together by DNA ligase redundancy - term to describe the genetic code bc most amino acids have more than one codon coding for them RNA structure - 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? - RNA polymerase binds to DNA at a promoter region (TATA box in humans) what happens during post-transcriptional process of mRNA? - 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 PCAT General Chemistry exam review questions and answers ribosomes - 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? - - 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? - humans and bacteria have diff types of subunits that make up their ribosomes. Antibiotic can target specific bacteria ribosome leaving human cells unharmed proteins - 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 - 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 PCAT General Chemistry exam review questions and answers Is the alpha carbon on an amino acid a chiral center? - yes except for glycine bc it has a H as its R group zwitterions - neutral form of an amino acid that has both positive and negative charges amphoteric - 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 - kal and ka2 2 dissociation constants when amino acids are deprotonated - kbl and kb2 isoelectric point (PI) or isoelectric pH - intermediate pH at which amino acids is neutral and exists as a zwitterion. lies between pKal and pKa2 ___ moles of base must be added to deprotonate 1 mole of most amino acids - two PCAT General Chemistry exam review questions and answers beta-pleated sheets - 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 - 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 - 2 cysteine molec became oxidized to form cystine. create loops in protein chain fibrous proteins - ex: collagen sheets or long strands globular proteins - ex: myoglobin spherical in shape conjugated proteins - 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 PCAT General Chemistry exam review questions and answers denaturation - proteins lose their 3D structure and revert back to random-coil state. caused by detergent or changes in pH, temp, or solute [] lipids - - 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 - having hydrophilic and hydrophobic regions. ex: phospholipids are amphipathic saturated fatty acid tails - have only single bonds. more stable and form solids at room temp unsaturated fatty acid tails - have 1+ double bonds that create kinks in the fatty acid chains. tend to be liquid at room temp. most are cis configuration PCAT General Chemistry exam review questions and answers glycerophospholipids - 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 - 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 - esters of long chain fatty acids with long chain alcohols. protect against environ. help prevent dehydration and provide lubrication signaling lipids - steroids, prostaglandins, and fat-soluble vitamins steroids - 4 cycloalkane rings fused together, non polar. cholesterol - important steroid. major component of phospholipid bilayer and helps maintain fluidity. helps stabilize cell membrane against changes in temp (high temp=membrane not too permeable. low temp= keeps membrane from solidifying) PCAT General Chemistry exam review questions and answers mass defect - diff in the larger mass for the constituent protons and neutrons of original nucleus in nuclear rxn radioactivity - when the nucleus of an atom is unstable, it can spontaneously emit particles or electromag radiation how are nuclear rxns diff from chem reactions? - 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? - iron bc the binding E per nucleon peaks here how does fission nuclear reaction work? - 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 - 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 PCAT General Chemistry exam review questions and answers 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? - alpha decay and fission beta decay - emission of either a beta- (electron) or b+ (positron) from the nucleus positron - similar to an e- (minimal mass) but has a positive charge beta - decay - 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 - 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 - 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 # PCAT General Chemistry exam review questions and answers electron capture - 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