exam 1 Flashcards
Na atomic number, electron configuration
11p, 11n, 11e, 1s2 2s2 3p6 3s1
Na+ atomic #, electron config
11p, 11n, 10e, 1s2 2s2 2p6
one orbital in…
first shell
max of electrons in first row of elements’ orbital?
2 electrons
VSEPR (valence shell electron pair theory) is
electrons repel each other
orbitals don’t repel each other (can’t be in same place as another orbital)
fill 1st orbital before moving to the next
bonding is…
the arrangement of two atoms in stable organization
through bonding, atoms attain..
a complete outer shell of valence electrons and lower energy configuration
ionic bonds come from the transfer of…
electrons from one element to another
covalent bonds result from…
sharing of electron b/w two nuclei
ionic bonds come from…
electrostatic attraction b/w two charged species
ionic stability relates to
noble gas configuration
coloumb’s law shows the…
energy release when salt is formed from ions
second row elements can’t have more than…
8 electrons around them
consequences for neutral molecules?
1) atoms with 1/2/3 valence electrons from 1/2/3 bonds in neutral molecules
2) atoms w/ 4+ valence electrons form enough bonds to make an octet
how to calculate predicted # of bonds?
8 - # of valence electrons
when second row elements form >4 bonds…
their octets consist of both bonding (shared electrons) and nonbonding (lone pairs) electrons
lewis structures use…
lines to represent covalent bonds (shared electrons) and dots to represent unshared electrons (lone pairs)
formal charges are (x) specific
atom
formal charges are…
the charge assigned to individual atoms in a lewis structure
formal charge =
of valence electrons - # of electrons an atom “owns”
number of electrons owned by an atom is determined…
by its number of bonds and lone pairs
an atom “owns” all of its…
unshared electrons and 1/2 of its shared electrons
FC =
valence - sticks - dots
lower energy means
more stability
free radicals are….
more reactive b/c they don’t have an octet (they violate the octet rule)
isomers have the same molecular…
formula but completely different structures aka constitutional isomers
bond length decreases…
across a row as atom size decreases
bond length increases…
down a column as atom size increases
force of atom is stronger when…
electrons are closer
smaller atoms have…
smaller covalent bonds
larger atoms have…
larger covalent bonds
bond angle determines…
shape around any atom bonded to two other atoms
group is either an atom or…
a lone pair of electrons
number of groups surrounding a particular atom is called
geometry
stable arrangement keeps groups…
far away –> VSEPR (valence shell electron pair repulsion theory)
two groups:
linear, 180 degrees
three groups:
trigonal planar, 120 degrees
four groups:
tetrahedral, 109.5 degrees
skeletal structures:
- assume there’s a C atom at junction of any two lines/line
- assume enough H around each C to make each C tetravalent
- draw heteroatoms and H directly bonded to them
a heteroatom is an atom…
without hydrogen and carbons
sigma bonds form when…
1s orbital of 1 H overlapping with 1s orbital of another H atom
sigma bond concentrates…
electron density b/w 2 nuclei formed
sigma bond is…
cylindrically symmetrical
constructive interference has…
lower energy
destructive interference has…
higher energy
what is hybridization?
combination of 2+ atomic orbitals
larger lobe =
stronger bond
bond rotation occurs around…
central C-C sigma bond (no double or triple bonds)
C-H and C-C bonds are
sigma bonds
overlap of 2p orbitals =
2nd C-C bond (more likely to break)
polarity of molecules
determines if molecule has a net dipole
polar molecule has one…
polar bond or 2+ bond dipoles that reinforce each other
coulomb’s law shows…
relation b/w force and energy of charged species (ions) with distance
same charge ions have…
+ delta E (bad)
ions of opp signs have
negative delta E (good)
closer ions =
stronger effect
lots of phenomena occurs to…
get low E
major elements?
C, N, O, H
minor elements?
halogens (F, Cl, Br, I), S, P, Si, metals
what is an atom?
building block of matter
what is a bond?
a stable joining of two atoms (via 2 electrons)
what is atomic mass?
average of all isotopes based on population
elements in the same row are roughly…
the same size
left to right means
elements get smaller in size
elements in the same column have roughly…
the same reactivity
as row number increases,
element rarity increases
chemical reactivity is based on
electrons in atomic orbitals
atomic orbitals are
locations where electrons can be found
orbitals can change shape but not…
number
i.e. an s and p orbitals can become 2 sp orbits (NOT 1 sp orbital)
shape of s orbital?
sphere
shape of p orbital?
dumbell
what is electron configuration?
arrangement of electrons in orbitals
shells are groups of orbitals…
increasing size and energy
group number tells you the number of…
outermost electrons
filled shells are thermodynamically…
favorable (noble gas configuration)
bonding allows completed…
outer shells / noble gas configuration (attempt to reach 8e- shells)
ionic bonding is
unshared electrons held together by strong electrostatic forces
covalent bonding
shared electrons
excess electrons manifest as…
nonbonding electron pairs
representation of molecules with electrons is called
lewis dot structures
lewis dot structures rules
1) draw only valence electrons around symbol
2) after that, give second row e- a full octet if possible
3) give each H 2e- if possible
4) may need to form double or triple bonds to 2nd row elements to form full octet
never draw 5 bonds around…
CARBON
how to calculate formal charge?
valence electrons - sticks - dots
what are isomers?
same elements, different connectivity/structure
constitutional isomers are
isomers with different connectivity
molecular geometry:
two groups (linear, 180 deg)
three groups (trigonal planar, 120 deg)
four groups (tetrahedral, 109.5 deg)
120 deg =
trigonal planar = flat
109.5 deg =
3D = tetrahedral
hybridized orbitals
atomic orbitals blend (mix) to become molecular orbitals
atomic orbitals overlap …
to form molecular orbitals
s can overlap with
sp, sp2, sp3 to form a sigma bond
p can overlap with
sp, sp2, sp3 to form a pi bond
s cannot overlap with
p
4 sigma bonds –>
sp3 (tetrahedral, 109.5)
3 sigma bonds are related to what hybridization?
sp2 (trigonal planar, 120)
2 sigma bonds
sp (linear, 180)
treat a lone pair like a
sigma bond
1 double bond implies
sp2 hybridization
1 triple bond implies
sp hybridization
pattern for carbon bonds:
increasing bond strength
decreasing bond length
sp3 bonds are longer than
sp2 bonds which are longer than sp
electronegativity is
an atom’s attraction for electrons in a bond
electronegativity increases
up and to the right of the periodic table
covalent bonds between atoms of different elements are not
equally shared
C-H bonds are not really polar covalent bonds because…
C and H have roughly the same polarity
polar molecules possess a
dipole (sum of polar forces of polar bond)
solubility of covalent molecule
polar solvent dissolve polar compounds and will NOT dissolve nonpolar compounds
bronsted-lowry acid is a
proton (H+) donor
bronsted-lowry base is a
proton (H+) acceptor
acids often have a
+ or neutral charge
bases often have a
negative or neutral charge
bronsted lowry acid possesses what kind of proton?
donatable proton
bronsted lowry base possesses a
lone electron pair or a pi bond
is water a bronsted lowry acid or base?
depends on environment
lewis acid is an electron pair acceptor or donor?
electron pair acceptor
lewis base is an
electron pair donor
is water a lewis acid or base?
depends on environment
bronsted lowry acid base reactions involve the
transfer of a proton (normally must break a bond to form a bond)
an acid that loses a proton
forms a weak conjugate base
a base that gains a proton
forms a weak conjugate acid
pka is
the quantitative measure of acid strength
larger Ka =
more acidic something is
small pka =
more acidic something is
pka =
-log Ka
pka is a pH but it is
the acid strength for an individual compound
pH is the acid strength of an environment (like a buffer solution)
weak acid does not automatically mean
a strong base
strong acids readily donate or accept protons?
donate protons
do weak acids donate or accept protons?
donate protons
predicting acid-base reactions:
reactions ALWAYS go strong to weak
factors that affect acidity?
elemental
inductive effects (electronegativity)
resonance
hybridization (pi electrons)
as you go right on the periodic table…
electronegativity increases, product stabilizes
charges are stabilized when on
larger ions
inductive effects signify the
presence of electronegative atoms increase acidity
the more electronegative,
the more acidity
the closer an electronegative atom is,
the more acidity
hybridization effects state the more ‘s’ character
the more acidic
more ‘s’ character, the more
(-) charge is held
resonance structure are 2 (or more) lewis structures that
have the same placement of atoms but a different arrangement of pi electrons
are resonance structures real?
they are model; reality is a hybrid of the structures
rules of resonance #1
atoms and sigma bonds must stay in the same positions (pi bonds and lone pairs may vary in location)
rules of resonance #2
two resonance must have same number of unpaired electrons
rules of resonance #3
resonance structures must be valid lewis structures
predicting resonance structures:
- use curved arrows to ‘shift’ pi bonds or lone pairs
- leave all sigma bonds alone
electrons move to location where
room for electrons allows
- can only move 1 bond distance
electrons can move
neg to neutral
neg to +
neutral to +
BUT NOT + to neutral/-
resonance stabilizes
structures (makes them lower in energy)
if you have resonance…
your structures are stable
the higher the pka of the acid,
the stronger the resultant base
lewis bases need
free pair of e- (lone pair or pi bond)
lewis acids need room to accept
lone pairs (including breaking bonds)
lewis acids are also known as
electrophiles
lewis bases are also known as
nucleophiles
curved arrows are used to indicate
movement of electrons
an electron deficient carbon reacts with a
nucleophile (Nu-)
electron rich carbon reacts with an
electrophile (E+)
alkenes contain an electron rich double bond so they react with
electrophiles (E+)
a lone pair on a heteroatom makes it
basic and nucleophilic
pi bonds create (x) and are more…
nucleophilic sites, easily broken than sigma bonds
alkanes are aliphatic hydrocarbons having
C–C and C–H sigma bonds
acyclic alkanes have the molecular formula:
C n H 2n+2 where n = an integer
- contain only linear and branched chains of carbon atoms
saturated hydrocarbons are
acyclic alkanes that have the max number of hydrogen atoms per carbon
cycloalkanes contain
carbons joined in 1+ rings
cycloalkanes’ general formula?
C n H 2n (have two fewer H atoms than an acyclic alkane with the same number of carbons)
all C atoms in an alkane are surrounded by
four groups (making them sp3 hybridized and tetrahedral, bond angles are 109.5)
butane and isobutane are…
constitutional isomers
same molecular formula, different arrangement
constitutional isomers are
isomers that differ in the way the atoms are connected to each other
- they are two different compounds with the same molecular formula
carbon atoms in alkanes are classified by….
the number of other carbons directly bonded to them
primary carbon
carbon is bonded to one other C atom
secondary carbon
carbon is bonded to two other C atoms
tertiary carbon
carbon is bonded to three other C atoms
quarternary carbon
carbon is bonded to four other C atoms
hydrogen atoms are classified as
primary, secondary, tertiary
primary hydrogen
H is on a C bonded to one other C atom
secondary hydrogen
H is on a C bonded to two other C atoms
tertiary hydrogen
H is on a C bonded to three other atoms
CH4
1 C atom
n-alkane: methane
C2H6
2 C ATOMS
ETHANE
C3H8
3C
PROPANE
C4H10
4C
BUTANE
2 CONST ISOMERS
C5H12
5C
PENTANE
3 CONST ISOMERS
C6H14
6C
HEXANE
5 CONST ISOMERS
C7H16
7C
HEPTANE
9 CONST ISOMERS
C8H18
8C
OCTANE
18 CONST ISOMERS
C9H20
9C
NONANE
35 CONST ISOMERS
C10H22
10C
DECANE
75 CONST ISOMERS
C20H42
20C
EICOSANE
366,319 CONST ISOMERS
cycloalkanes
molecular formula: C n H 2n
- contain carbon atoms arranged in a ring
C3H6
cyclopropane
cyclobutane
C4H8
C5H10
cyclopentane
cyclohexane
C6H12
naming organic molecules
1) parent name (number of carbon in longest continuous chain)
2) suffix - func groups present
3) prefix tells: identity, location, number of substituents attached to the carbon chain
prefix +
parent + suffix
what is CH2 group commonly known as?
methylene
what are alkyl groups?
carbon substituents bonded to a long carbon chain
alkyl group is formed by
removing one H atom from an alkane
how to name an alkyl group?
1) change –ane ending of parent alkane to —yl
2) thus methane (CH4) becomes methyl (CH3-) and ethane become ethyl
if there are two chains of equal length..
pick the chain with more substituents
number the atoms in the carbon chain to give the substituent the (x) number?
lowest
if the first substituent is the same distance from both ends, number the chain to give….
the second substituent the lower number
when numbering the carbon chain results in the same numbers from either end of the chain…
assign the lower number alphabetically to the first substituent
substituents in a carbon chain get named as…
alkyl groups
what is combined to create the IUPAC names of compounds/molecules?
combine substituent names and numbers + parent and suffix
cycloalkanes are named using similar nomenclature rules but…
the prefix cyclo- immediately precedes the name of the parent
naming cycloalkanes:
1) find the parent cycloalkane
2) name/number the substituents (no number is needed to indicate the location of a single substituent)
3)
for rings with more than one substituent..
begin numbering at 1 substituent and proceed around the ring to give the second substituent the lowest number
numbering the ring with two different substituents consists of…
numbering the ring to assign the lower number to the substituents alphabetically
special case of an alkane composed of both a ring and a long chain…
if the number of carbons in the ring is greater than or equal to the number of carbons in the longest chain –> CYCLOALKANE
do alkanes have high or low boiling points?
LOW
boiling point (x) as the number of carbons (y)
increases, increases b/c of increasing surface area
the boiling point of isomers decreases with branching because of…
decreased surface area
alkanes have low…
melting points (compared to more polar compounds of comparable size)
melting point increases as the number of…
carbons increases (b/c of increased surface area)
melting point increases with…
increased symmetry
solubility of alkanes?
alkanes are soluble in organic solvents and water
conformations are…
different arrangements of atoms that are interconverted by rotation about single bonds
when naming acyclic alkanes…
names are given to two different conformations
eclipsed conformation:
C–H bonds on one carbon are directly aligned with the C–H bonds on the adjacent carbon
staggered conformation:
C–H bonds on one carbon bisect the H–C–H bond angle on the adjacent carbon
on the eclipsed conformation…
the C–H bonds are all aligned
on the staggered conformation:
the C–H bonds in front bisect the H–C–H bond angles in the back
what can convert an eclipsed conformation into a staggered one?
rotating atoms on one carbon by 60 degrees
dihedral angle
angle that separates a bond on one atom from a bond on an adjacent atom
newman projection:
end-on representations for conformations
staggered conformations are more…
stable (lower in E) than eclipsed conformations
electron-electron repulsion b/w bonds in the eclipsed conformation…
increases its energy compared with the staggered conformation (where bonding electrons are farther apart)
when C–H bonds are farther apart,
molecule is more stable
torsional energy
energy difference between staggered and eclipsed conformers
torsional strain
increase in E caused by eclipsing interactions
an energy min and max occur every
60 degrees as the conformation changes from staggered to eclipsed
staggered conformation with two larger groups 180 degrees from each other is…
ANTI
staggered conformation with two larger group 60 degrees from each other is…
GAUCHE
which are lower in E: staggered or eclipsed?
staggered
relative energies of the individual staggered conformations
depend on their steric strain
what is steric strain?
increase in E resulting when atoms are forced too close to one another
are gauche or anti conformations higher in E?
gauche, because of steric strain
what is barrier to rotation?
energy difference b/w the lowest and highest energy conformations
lowest energy conformation has all bonds….
staggered and all large groups anti
- alkanes are often drawn in zigzag skeletal structures to indicate this
angle strain is…
the increase of energy when bond angles deviate from the optimum tetrahedral angle of 109.5 degrees
cycloalkanes with more than three C atoms in the ring are…
puckered to reduce strain
chair conformation is stable or unstable?
STABLE
chair conformation is so stable because it…
eliminates angle strain (all C–C–C angles are 109.5) and torsional strain (all Hs on adjacent C atoms are staggered)
axial hydrogens are located…
above and below the ring along a perpendicular axis
equatorial hydrogens are located…
in the plane of the ring around the equator
ring-flipping is an
important conformational change in cyclohexane
in a ring flip, what changes?
axial H –> equatorial H
equatorial H –> axial H
up to down carbons
down to up carbons
boat conformation is destabilized by…
torsional strain b/c the hydrogens on the four carbon atoms in the plane are eclipsed
chair forms are (x) more stable than boat forms
7 cal/mol
the equatorial position has more…
room than the axial position (larger substituents are more stable in the equatorial position)
larger axial substituents create…
destabilizing 1,3-diaxal interactions
what destabilizes boat conformation?
torsional strain b/c Hs on 4 carbon atoms in plane are eclispd
larger substituents are more stable in the…
equatorial positions
stereoisomers are isomers that…
differ only in the way the atoms are oriented in space
prefixes that are used to distinguish stereoisomers?
cis and trans
cis isomers has two groups on the
same side of the ring
trans isomers have two groups on….
opposite sides of the ring
all disubstituted cycloalkanes with two groups bonded to…
different atoms have cis and trans isomers
alkanes are the only family of organic molecules that have no…
functional group (they undergo very few reactions)
alkanes undergo…
combustion
combustion is an…
oxidation-reduction rxn
oxidation is the loss of
electrons
reduction is the gain of
electrons
to determine if an organic compound undergoes oxidation or reduction, we…
concentrate on the carbon atoms of the starting material and production
- compare the relative number of C-H and C-Z bonds where Z = an element more electronegative than carbon (O, N, X)
oxidation results in an increase of
C-Z bonds
oxidation results in a decrease of
C-H bonds
reduction results in a decrease of
C-Z bonds
reduction results in an increase of
C-H bonds
alkanes undergo combustion, meaning they
burn in the presence of oxygen to form CO2 and water
