exam 1 (chapters 1 & 2)

Question 1

atomic number

Answer 1

number of protons in the nucleus

Question 2

isotopes

Answer 2

same number of protons but different number of neutrons

Question 3

electronegativity

Answer 3

ability of an atom to attract electrons (shared electrons in a covalent bond)

• atoms with large electronegativity difference react with each other (if the electronegativity difference is a lot, then both electrons will be donated becoming an ionic bond
• covalent bonds form by sharing of electrons between atoms of similar/same electronegativities

Question 4

how to calculate formal charge

Answer 4

number of electrons its supposed to have minus the amount it has in the diagram

• double bond counts as 2 and so does lone pair (b/c its about how many electrons are attached to the actual atom - one is its own and the other is the other element’s)

Question 5

charge on carbon, nitrogen, oxygen, and chlorine (halogens) and what they look like

Answer 5

carbon
+ = 3 bonds only
neutral = 4 bonds
- = 3 bonds, 1 lone pair

nitrogen
+ = 4 bonds
neutral = 3 bonds, 1 lone pair
- = 2 bonds, 2 lone pairs

oxygen
+ = 3 bonds, 1 lone pair
neutral = 2 bonds, 2 lone pairs
- = 1 bond, 3 lone pairs

chlorine (halogens)
+ = 2 bonds, 2 lone pairs
neutral = 1 bond, 3 lone pairs
- = 4 lone pairs

Question 6

how to tell which resonance structure contributes more to the overall hybrid

Answer 6

• complete octets: structures where most elements (esp C, N, O) have full octets are more stable
• minimal formal charges: structures with the least amount of formal charges are more stable
• if theres charge, better for neg. charge to be on electronegative atoms and pos. charge to be on less electronegative atoms (like C)
• electronegative atoms can contain a pos. charge only if they have a complete octet

Question 7

exceptions to the octet rule

Answer 7

elements in the second row usually obey the octet rule (Li, Be, B, C, N, O, F) as they have 1 2s and 3 2p orbitals available for bonding

elements in 3rd period and beyond have d orbitals that can accommodate for more and may not obey octet rule (ex. Sulfur)

electron-deficient exceptions: BF3 (where B is missing 1 bond b/c flourine doesnt want to give it up). also B is smaller and less electronegative so it lowkey doesnt even want more
- these types are better catalysts - also AlCl3
- also becomes highly reactive to get more (but idk why)

Question 8

isomers + constitutional isomers

Answer 8

isomers: different compounds that have the same molecular formula

constitutional isomer: isomers that have the same molecular formula but different connectivity (their atoms are connected in a different order) & their properties are completely different
- ex. 1-chloropropane and 2-chloropropane

Question 9

dashes & wedges

Answer 9

dashed: bond projects behind plane (going backwards)

wedge: bond projects out of the paper (towards you)

• an ordinary line represents a bond that lies within the plane of the paper

are multiple ways to write them, dashes and wedges can alternate between different elements b/c everything is always moving

Question 10

are intersections carbon points?

Answer 10

no, because the line has to change direction for it to be carbon, a straight line intersecting with another is not a carbon

Question 11

how many carbons are in a triple bond drawing

Answer 11

2 carbons (1 at each end of the triple bond)

Question 12

significant resonance structures: exception of nitro group

Answer 12

• nitro group (NO2) will often have significant resonance structures with more than 2 charges
• even though you’re supposed to minimize charges with significant structures, nitro group can have more than 2 charges and still be significant
• 2 charges of nitro group don’t count

Question 13

significant resonance structures: exception of electronegative atoms bearing positive charge

Answer 13

• electronegative atoms (N, O, Cl, etc.) prefer to have a negative charge but they can take a positive charge if they have a complete octet
• then, that structure ends up being more significant if the octet is complete and they have a positive charge

Question 14

significant structures: carbons with opposite charges

Answer 14

• one structure cannot have both C+ and C- whether close or far apart!!
• it would not be a significant structure then

Question 15

bond angles in relation to hybridization

Answer 15

sp3 = tetrahedral = 109.5º
sp2 = trigonal planar = 120º
sp= linear = 180º

Question 16

difference between aldehyde and ketone

Answer 16

both have =O to C

• but ketone is that the C=O is attached to 2 other carbons
• aldehyde is that the C=O is attached to C and H

Question 17

allylic carbon

Answer 17

bonded to a carbon atom that is double bonded to another carbon atom

allyl carbocation: where the positive charge is distributed between carbons in resonance and the double bonds alternate basically

Question 18

how to spot 0 formal charge without calculating

Answer 18

looks or their normal number of bonds

carbon: 4 bonds
nitrogen: 3 bonds + 1 lone pair
oxygen: 2 bonds + 2 lone pairs
hydrogen: 1 bond

Question 19

Aufbau principle, Pauli exclusion principle, Hund’s rule

Answer 19

aufbau principle: orbitals are filled so that those of lowest energy are filled first (aufbau means stacking up in Germany)

pauli exclusion principle: maximum of 2 electrons can be placed in each orbital but only when the **spins of the electrons are opposite*

hund’s rule: degenerate orbitals (orbitals of the same energy level) - add 1 electron to each with their spins unpaired until all of them fill up and then double up

Question 20

how are bonding and anti bonding molecular orbitals formed?

Answer 20

bonding molecular orbital: results when 2 orbitals of the same phase overlap

antibonding molecular orbital: results when 2 orbitals of the opposite phase overlap

• electrons prefer to be in bonding orbitals b/c they’re more stable, they dont really use the antibonding ones

Question 21

pi bonds and sigma bonds overlap

Answer 21

• pi bonds overlap laterally always
• sigma bonds overlap head on

Question 22

constructive & destructive interference

Answer 22

constructive: happens when 2 orbitals (regions where electrons are found) match up perfectly, pos. overlap w/ pos., resulting lobe is bigger, forms bonding molecular orbital

destructive: happens when 2 opposite orbitals overlap (+ and -), results in smaller lobe formed and forms antibonding orbital - electrons dont like to hang out here

Question 23

a situation where cis/trans isomerism is not possible

Answer 23

when 1 carbon of the double bond has 2 identical groups (the groups have to be on opposite carbons, otherwise cis/trans isomerism is not possible)

Question 24

atomic vs molecular orbital

Answer 24

atomic orbital: region of space about the nucleus of a single atom where there is a high probability of finding an electron

molecular orbitals: when atomic orbitals overlap, they combine to form a molecular orbital (basically a bond) - can be either bonding or antibonding

Question 25

shape of molecule based on: - sp - sp2 - sp3 - sp3 w/ lone pair - sp3 with 2 lone pairs

Answer 25

**sp**: linear **sp2**: trigonal planar **sp3**: tetrahedral **sp3 w/ lone pair**: trigonal pyramidal **sp3 with 2 lone pairs**: angular (bent)

Question 26

general formula for alkanes, alkenes, alkynes, & cyclic alkanes (rings)

Answer 26

**alkanes**: Cn H2n+2 **cyclic alkanes**: Cn H2n (b/c you have to remove 2 H molecules to form a ring) **alkenes**: Cn H2n **alkynes**: Cn Hn

Question 27

polar covalent bonds

Answer 27

**polar covalent bonds**: electrons of different electronegativity combine with each other = electrons are not shared equally = creates dipole moment - just b/c a molecule has a polar bond does not make It a polar molecule as a whole b/c the dipoles of the bonds can cancel out (with symmetry)

Question 28

dipole moment in alkenes (cis/trans)

Answer 28

alkenes = double bond

Question 29

boiling point & melting point correlation for molecules

Answer 29

**higher boiling point**: want it to be linear for higher boiling point,if symmetrical and can pack closer together then also have higher boiling point (trans molecules) **higher melting point**: want it to be spherical for higher melting point, if non-symmetrical and can't pack together then higher melting point (cis molecules)

Question 30

-ane vs. -yl for alkyl groups

Answer 30

**-ane**: for when the molecule by itself like butane, methane **-yl**: for when the molecule is missing an H (where it would bond) with the next molecule

Question 31

phenyl vs benzyl + phenol vs. benzyl alcohol

Answer 31

**phenyl**: just a benzene ring (6 carbon ring with alternating single and double bonds) attached directly to something else, like atom or molecule **benzyl**: a phenyl group (benzene ring) with an extra -CH2- **phenol**: benzene ring attached to -OH group directly **benzyl alcohol**: benzene ring attached to CH2 that is then attached to OH

Question 32

iso- vs, sec- vs. tert-

Answer 32

**iso-**: molecule has a branch at the end, specially second to last carbon, creates a "Y" shape **sec- (secondary)**: group is attached to carbon atom that is connected to *2 other* carbon atoms, attached usually in the middle of the chain not the end **tert- (tertiary)**: group is attached to carbon atom that is connected to 3 other carbon atoms, creates a more branched and compact structure

Question 33

primary, secondary, tertiary carbons

Answer 33

**primary**: carbon is bonded to 1 other carbon atom, the rest are different molecules (H's) **secondary**: carbon is bonded to 2 other carbon atoms **tertiary**: carbon is bonded to 3 other carbon atoms - also quaternary carbons, but thats not rlly frequently used **only possible if carbon is sp3 hybridized, otherwise no classification**

Question 34

alkenyl vs aryl halide

Answer 34

**alkenyl halide**: halide group (halogen atom) is bonded to an alkene (double bond) carbon **aryl halide**: halide group is bonded to an aromatic ring (alternating double-single bonds)

Question 35

primary, secondary, tertiary alcohols

Answer 35

**primary alcohol**: OH group is attached to a carbon that is bonded to 1 other carbon **secondary alcohol**: OH group is attached to a carbon that is bonded to 2 other carbons **tertiary alcohol**: OH group is attached to a carbon that is bonded to 3 other carbons

Question 36

primary, secondary, tertiary amine

Answer 36

**primary amine**: nitrogen atom itself is bonded to 1 carbon **secondary amine**: nitrogen atom is bonded to 2 other carbons **tertiary amine**: nitrogen atom is bonded to 3 other carbons **only works if nitrogen is sp3 hydridized, otherwise can't classify**

Question 37

nitriles

Answer 37

triple bonded Nitrogen to Carbon group (with a lone pair on nitrogen)

Question 38

how do you tell which compounds are going to be liquids or gases at room temp?

Answer 38

Liquids - organic compounds of **5-12 carbon atoms ( molecule weight 70-150** or low molecular weight but lots of **hydrogen bonding** - these tends to be liquids at room temp - if lots of hydrogen bonding + can pack well (I.e. long flat plans molecule) then these compounds can be solids

Question 39

When is cis/trans isomerism not possible?

Answer 39

When one of the carbons has 2 identical groups - the identical groups have to be on different carbons