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CHM 255 Exam 1
| Question | Answer |
|---|---|
| Each electron shell contains ______ electrons. | 2n^2 |
| What are the 3 rules for filling orbitals | 1. Fill lower electron energy orbitals 1st 2. No more than 2 electrons/ orbital 3. Fill all orbitals with same energy with 1 electron before putting into 2nd |
| Describe the shapes of s and p orbitals | S-orbital: spherical P-orbital: 2 lobes |
| Define electronegativity | how tightly an atom holds on to its electrons |
| What is the most electronegative atom and it's value | Flourine; 4.0 |
| Electronegativity trend | Increase right and up |
| Differentiate between ionic and covalent bonding | Ionic: electron transfer; eneg. diff. > 1.9 (large) Covalent: electron share; eneg. diff. <1.9 (>0.5 = nonpolar) |
| How can you tell if an atom has a partial negative or positive charge? | The more electronegative atom has a partial negative |
| Know electron configuration; lewis structure | |
| Formal charge formula | (Initial # valence electron) - (# nonbonded electron) - (1/2)(# bonded electron) |
| * FORMAL CHARGE CHART * | |
| Define alkane, alkene, and alkyne | Alkane: single CH bonded chain Alkene: CH chain with double bond(s) Alkyne: CH chain with triple bond(s) |
| Alcohol | OH (hydroxl) group |
| Ether | single bonded C-O-C |
| Amine | Single bonded N-H on chain |
| Aldehyde vs. Ketone | Aldehyde: R-C=O(-H off C also) at the END Ketone: R-C=O(R' off C also) in the middle |
| Carboxylic acid | R-C=O(-OH on C also) |
| Ester | R'-C(=O)-O-R |
| Amide | R"-C(=O)-N-R(R') |
| Phosphate Ester | Central P with =O, 2 O-, and O-R bonded at four sides Holds DNA together |
| What are bond angles and the shape of molecules dictated by? | A desire to keep the valence shell electrons as far away from one another as possible |
| Tetrahedron | 4 atoms or electron pairs bond angle 109.5 |
| How do unpaired electrons affect bond angles | Lead to greater repulsion and change angles |
| Trigonal Planar | 3 atoms or electron pairs bond angle 120 |
| Linear arrangement | 2 atoms or electron pairs bond angle 180 |
| An atomic orbital determines _____ % probability to find and electron there | 90 |
| Two 1s orbitals form a _____ bond Two 2p orbitals form a _____ bond | Sigma; Pi |
| Hybridization of atomic orbitals | Number of electron dense areas... 4=sp3 3=sp2 2=sp |
| How many sigma & pi bonds? a. sp3 b. sp2 c. sp | a. 4 sp3 --> 4 sigma b. 3 sp2 + 1 p ---> 3 sigma; 1 pi c. 2 sp + 2 p ---> 2 sigma; 2 pi |
| Which are hybridized, atoms or bonds? | Atoms |
| Describe resonance | The real structure of a molecule (resonance hybrid) is a composite of contributing structures |
| In arrow pushing, where does the arrow start? | The site of the electrons you want to move |
| Preference in resonance structures given by what 4 things? | 1. Atoms with completed octets 2. Maximum # covalent bonds 3. Least separation of unlike charges 4. Negative charge on more electronegative atom |
| Electronegativity: C, H, N, O, F, Cl, Br | C: 2.5; H: 2.1; N: 3.0; O: 3.5; F: 4.0; Cl: 3.0; Br: 2.8 |
| Prefixes for 1-10 Carbons | 1-meth; 2-eth; 3-prop; 4-but; 5-pent; 6-hex; 7-hept; 8-oct; 9-non; 10-dec |
| Infixes for IUPAC naming | Indicates nature of C-C bonds an- all single bonds en- double bond(s) yn- triple bond(s) |
| Suffix for each functional group in IUPAC (hydrocarbon, alcohol, aldehyde, ketone, carboxylic acid) | e-hydrocarbon; ol-alcohol; al-aldehyde; one-ketone; oic acid-carboxylic acid |
| Intermolecular forces of attraction are known as ____________: caused by temporarily induced dipole moments in atoms and molecules | dispersion forces |
| What causes boiling point to increase? | The number of atoms and most branching |
| What creates a temporary electron dipole? | Unsymmetrical electron density |
| The boiling point of a compound is ___________. ________ is needed to overcome attractive forces that occur in the liquid state. | The temperature at which liquid molecules are converted into gas; Energy |
| Define conformation | any 3_d arrangement of atoms that results from rotation around single bonds |
| The conformations that we care about are the ___________ (least favorable) and ________ (most favorable) | highest energy; lowest energy |
| To draw a _____________ look down the C-C bond and flatten | Newman Projection |
| In the _________ conformation H's are as far apart as possible In the _________ conformation H's are on top of each other | staggered; eclipsed |
| Which has the highest energy, eclipsed or staggered conformation? | eclipsed |
| Eclipsed conformation has ________ _______. | Torsional strain |
| What are the different types of staggered conformation and their relative energies | Lowest energy has CH3 groups farthest apart: "anti" Other ways to arrange staggerd are ~0.9kcal/mol higher in energy: "gauche" |
| What are the different types of eclipsed conformation and their relative energies | 2 conformations with CH3 groups not as close as possible ~ 3.5 kcal/mol higher than "anti" Highest energy structure has both CH3 groups eclipsed and is ~5kcal/mol higher energy than "anti" |
| What are constitutional isomers | molecules with the same molecular formula but a different arrangement of atoms |
| * Review substituent chains * (esp. iso, sec, tert) | |
| What do you do when there are two or more of the same substituents | 1. Number where the substituents are on the chain 2. Use prefix before substituent name (i.e. di, tri, etc.) |
| When both substituents are in equivalent positions, the one with _____________ gets the lowest number | the lower alphabetical ordet |
| Do you use prefixes when alphabetizing? | ONLY iso and neo |
| For cycloalkanes with one substituent... | don't use a number in naming, simply methylcyclo() |
| How do you number cycloalkanes with 2 or more substituents | Number the ring starting with the substituent with the lowest alphabetical order |
| Why are the hydrogens in O-H more acidic than the hydrogens in C-H3 in acetic acid? | Acidity increases with electronegativity! |
| How can you determine which direction an equilibrium of an acid base reaction wil lie? | Lies towards higher pKa |
| What's the trick for determining if you've numbered correctly in a multiple choice? | Want the number of substituents to add to the lowest possible number (i.e, 4,5,5 > 3,4,4) |
| What do we know about cyclopropane in terms of strain, shapes, and angles? | Carbons are planar with 60 deg. angles' lots of angle and torsional strain |
| Eclipsed CH's lead to ___________ strain; An angle less than _____ leads to angle strain. | torsional; 109.5 |
| What do we know about cyclobutane in terms of strain, shapes, and angles? | Butterfly shaped; 88 deg. angles; angle strain |
| What do we know about cyclopentane in terms of strain, shapes, and angles? | Envelope shaped; 105 deg. angles |
| What do we know about cyclohexane in terms of strain, shapes, and angles? | Most stable conformation is the CHAIR shape |
| What's the difference between axial and equatorial? | Ax: up and down on alternating carbons Eq: slanted on angles in the opposite direction of the axials |
| If all CH's are _____________ there is NO torsional strain | staggered |
| What's the highest energy conformation for a cyclohexane & 3 characteristics? | Boat (both ends point in same direction) Steric clashing; torsional strain; 6.5 kcal/mol higher energy than chair |
| What is the twist boat conformation? | A twists of the boat to relieve strain and sterics that i s1kcal/mol lower in energy than the boat conformation |
| What is steric clashing? | When -H H- are facing towards one another |
| Why are equitorial substituents prefered over axial | Axial provide steric interaction; Equitorial is 1.7 kcal/mol more stable |
| The __________ the substituent the worse the interactions | larger |
| What's the equation to determine free energy difference betqeen equitorial and axial substituents? | (Delta G) = -2.3 R T log(Keq) |
| When there are two substituents they can be on the same side (______) or opposite sides (________). | cis; trans |
| Which is the highest and lowest energy chair conformation - cis or trans? | Trans with axial = highest; trans with equitorial = lowest |
| When attempting to obtain the lowest energy conformation always put the larger group in ___________(axial/equatorial). | equitorial |
| Define delocalization | Spreading electron density over a large surface area |
| How do you determine which resonance structure would contribute the most to the hybrid (3) | WANT: 1. More covalent bonds 2. Least # lone pairs 3. Saturated carbons |
| Bronsted-Lowry acid | Proton donor |
| Bronsted-Lowry base | Proton acceptor |
| Bronsted-Lowry conjugate acid | Base accepts a proton (+) |
| Bronsted-Lowry conjugate base | Acid loses a proton (-) |
| Difference between week and strong acid/base | Strong completely donates/accepts H+; weak doesn't completely |
| How do we measure the strength of an acid? | pKa |
| When deciding if one acid is more acidic than the other you should...? | compare the stability of the conjugate bases |
| What determines conjugate base stabilization (4) | 1. Inductive effect 2. Resonance 3. Electronegativity of the atom with the anion (across) 4. Hybridization of the atom the anion resides on 5. Bond dissociation energy (down) |
| What is the inductive effect | When there is a nearby group that can pull electronegatively away from the central atom |
| As electronegativity increases, what happens to the stability of the conjugate base and why | Stabilized because it can better accommodate the negative charge |
| How does acidity change with bond energy down the periodic table and why? | Lower BDE = more acidic because of the overlab of the orbitals |
| How does hybridization affect conjugate base stability | sp lower in energy than sp2 or sp3... so more acidic |
Created by:
jkmccord11
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