Midterm 2 Flashcards
what is valence bond theory
Valence bond theory: Covalent bonds form through the sharing of electrons by adjacent atoms, when the electron orbits of the two atoms overlap.
how does the quality of valence electron overlap affect bonding
The energy of a covalent bond system depends on the quality of the overlap. If the two nuclei get too close together than the repulsive forces between them increase the energy of the system.
what are hybrid orbitals
A combination or merge of multiple different orbitals
Hybrid atomic orbitals allow us to apply the ideas of orbital overlap and valence bond theory to Polyatomic molecules.
When combining atomic orbitals to make hybrid orbitals, n atomic orbitals make n hybrid orbitals.
describe sp orbitals
For elements like beryllium which don’t have singly-occupied orbitals in its ground electronic state it will have trouble forming bonds. So it can promot a 2s electron to 2p, then both the 2s and 2p electrons become 2 different sp hybrid orbitals.
They have two lobes, one larger one, one smaller
how does phase affect hybrid orbitals
Orbitals of any kind can have a positive and / or negative portion based on the wave function in that region. When making hybrid orbitals, waves of the same sign get added in magnitude (constructive), and those opposite lose magnitude (destructive).
what are very simplified depictions of hybrid orbitals like and why
Usually only the larger lobe of a hybrid orbital interacts with other orbitals, so in very simplified depictions of Hybrid orbitals it might be the only part shown.
what are SP2 orbitals
when one s orbital and two p orbitals are hybridized they form three SP2 orbitals
these looks pretty similar to SP orbitals with one large lobe facing out in a trigonal planer shape, and one small lobe closer to the nucleus.
what are SP3 orbitals
When one s orbital and three p orbitals are hybridized they form four SP3 hybrid orbitals
the large lobes face out in a tetrahedral shape
what are SP3D orbitals
one s orbital + 3 p orbitals + one d orbital makes 5 SP3D orbtials (in a trigonal bipyramidal shape)
what are SP3D2 orbitals
one s orbital + 3 p orbitals + two d orbitals make 6 SP3D2 orbtials (in an octahedral shape)
what are sigma bonds
So far the covalent bonds have all been sigma bonds
These have head to head overlap
and cylindrical symmetry of electron density about the internuclear axis
how does the number of electron domains tell us the Hybridization state of an atom
2 e- domains = Sp
3 e- domains = sp2
4 e- domains = sp3
5 e- domains = sp3d
6 e- domains = sp3d2
what are pi bonds
When describing multiple bonding, we must invole pi (π) bonds
these have side to side overlap
and electron density above and velow the internuclear axis
In single, double, and triple bonds what types of bonds do they have
Single bonds are always a sigma bond, since overlap is greater, making the bond stronger and more energy lowering
In multiple bonds, one is a sigma bond, the rest are pi bonds
So in triple bonds there is one sigma bond, then two pi bonds (one above the plan, and the other in the plane)
when are electrons delocalized
For atoms with resonance structure,
for an example the nitrate ion where all the atoms have a p orbital, and the three p orbitals of the oxygen atoms overlap with the p orbital on the central nitrogen. The πelectrons are delocalized throughout the ion.
Similar for benzene where the π electrons are delocalized throughout the ring.
why do we need molecular orbitals
Lewis structures, VSEPR theory, and hybridization still do not explain a few things.
ex: why does O2 interact with magnetic fields
why are some molecules coloured
how do we explain metallic bonding
Molecular orbital theory helps explain some of these observations
what is the difference between atomic and molecular orbitals
Electrons in atoms are found in atomic orbitals
electrons in molecules are found in molecular orbitals
how are molecular orbitals similar to atomic
Molecular orbitals are similar to atomic orbitals in a few ways:
- each contain 2 electrons with opposite spins
- each has a definite energy
- electron density distribution can be visualized with contour diagrams
how do we know how many molecular orbitals there are
when n AOS overlap, n MOs form, for hydrogen 1s (H) + 1s (H) must result in 2 MOs
what are the two different types of molecular orbitals
a destructive combination of AOS creates and anti-bonding orbital
while a constructive combination of AOS creates a bonding orbital
both have their electron density centred around the internuclear axis
in what order do electrons fill molecular orbit
Electrons will fill Molecular orbits starting with the bonding orbitals, each MO has space for 2 electrons
and they start from the most bonding bonding orbitals and move up
how do molecular orbitals tell us the H2 can exist and He2 not
So for hydrogen-hydrogen, it has 1 antibonding Orbital, and 1 bonding orbital. But since it only has 2 electrons, they both end up in the bonding orbital.
Since there is not antibonding electrons to cancel out the bonding ones, the H2 molecule is possible
For He2, there is 4 electrons to fill 2 MOS. meaning both anti-bonding and bonding orbitals hold 2 electrons. And they cancel out, preventing the He2 molecule from forming.
what is the formula for bond order
Bond order = 1/2 (no. of bonding electrons - no. of antibonding electrons)
how does molecular bonding explain solid sodium metal
Consider the element sodium, when a large number of sodium atoms are bonding, they each have 1 MO and 1 electron. So the total number of MO is equal to the total number of sodium atoms. There is also the same number of electrons to fill these MOs, but, since each MO can hold 2 electrons, they are only half fulled. And since the bonding ones fill up first, any number of Sodium atoms can bond together. creating solid sodium metal.
This is called band theory, since as you add more Na atoms to the chain, the space between orbitals gets smaller till you have a band.
why are metals conductive
The energy difference between molecular orbitals is tiny, so electrons can easily move between them, and throughout the metal. (this is why metals are conductive)
what happens in group 1-12 elements regarding band theory
In group 1-12 elements the s and d bands overlap so the total number of electrons flow to whichever states are lower in energy. The s, d electrons fill up to a common energy (like water in connected chambers)
what happens as you move along groups 1-12 in regards to band theory
the s band can hold up to 2 electrons per atom, the d band up to 10
Moving along from group 1-12 the s-d band fills with electrons.
For group 1-6 the bonding pair fill up, then from group 7-12 the antibonding fills up
what are the results of band theory in regards to metal toughness and melting points
this means that group 6 has the strongest metal-metal bonding, and are really hard and have high melting points. (ex tungsten)
Group 12 has all its bonding electrons cancelled out so its metal-metal bonding is minimized and the metals are soft (ex mercury)
what determines the conductivity of a materials, and what are the three broad categories it can have.
materials conduct electricity well if electrons can move from an occupied orbital to an unoccupied one easily.
In metals there is no gap between the valence band and the conduction band. so they conduct well
in materials like carbon, there is a small gap between these two bands. so they are semiconductors
other materials have a very large gap and so act as insulators.
what is organic chemistry
Organic chemistry is the branch of chemistry that studies carbon compounds
what are the two most common types of bonds in organic chemical
Carbon carbon bonds are the backbone of organic chemistry, but carbon hydrogen bond occur in almost all organic molecules
what determines the reactivity and function of an organic molecule
the shapes of organic and biochemical molecules are important in determining their physical and chemical properties
carbon carbon and carbon hydrogen bonds are non polar covalent bonds, that are quite strong and unreactive
A group of atoms that determines how an organic molecules functions is called a functional group
what are alkanes
contain only single covalent bonds between carbon atoms
Long chains of carbon with hydrogen filling in empty bonds
end in “ane”
how can you draw alkanes, alkenes, and alkynes in shorthand
Shorthand drawing: a “zigzag” / branching zigzag line where the end of every line is a carbon, bond angles are 120º ish and hydrogen are not drawn, but fill out every octet. two/three lines for double / triple bonds
what is the formula for non cyclic alkanes
The formula for non cyclic alkanes is CnH2n+2, where n can be any number. the higher the number for n is the higher the melting or boiling point is
what are the prefixes you need to know for naming hydrocarbon chains
Naming alkanes relies on the prefixes for 1-10
1 = meth
2 = eth
3 = prop
4 = but
5 = pent
6 = hex
7 = hept
8 = oct
9 = non
10 = dec
what is possible for hydrocarbons with more than 3 carbon
branched chain hydrocarbons are possible for alkanes with more than 3 carbon atoms. Use the same formula for branched alkanes
what are structural isomers
Structural isomers are compounds with the same molecular formula but different bonding arrangements
They have somewhat different physical and chemical properties
what are the three components of an alkanes name
the name has 3 parts: prefix - base - suffix
prefix = what substituents (parts attached to chain not just H atom)
base = how many carbons
suffix = what family
how do you name an alkane
to name a compound
- Find the longest carbon chain. (the one with the most substituents, if more than one)
- number the chain from the end nearest the first substituent encountered
- list the substituents as a prefix along with the number(s) of the carbon(s) to which they are attached; replace ane with yl for hydrocarbon attachements
- when two or more substituents are present, list them in alphabetical order (use prefixes, di, tri, penta, for more than one of the same substituent)
- Do not alphabetize the numerical part of prefixes (ex triethyl before methyl)
- use fluoro, chloro, bromo, iodo, for group 17 substituents
what are cycloalkanes
carbon can also form ringed structures, 5 and 6 are the most stable though smaller exist and are reactive and strained
can take on conformation in which angles are ~ tetrahedral
how reactive are alkanes and what are they used for
mostly unreactive due to only c-c c-h non polar covalent bonds
used as non polar solvents and for combustion
what are alkenes
unsaturated hydrocarbons that contain C and H with at least on Carbon carbon double bond.
Called unsaturated since they have less than the max number of hydrogen for that number of carbon
how do you name alkenes
Named in same way as alkanes but with suffix -ene not -ane.
The location of the double bond is indicated by a prefix
chain numbered so the double bond gets the smallest possible number
what do the double bonds in alkenes mean for isomers
Alkenes cannot rotate freely about the double bond (π bond = side to side overlap)
no rotation means geometric isomers are possible in alkenes, differ from each other in the spatial arrangement of groups about the double bond
what does cis / trans mean in regards to alkenes
this structure determines the physical properties of alkenes, such as their boiling points.
Cis = this side of
means both sides of the double bond are lined up
trans = the other side of
means the two side of the double bond are flipped
what are alkynes
unsaturated hydrocarbons with at least one carbon carbon triple bond
Carbons in the tripled bond are sp-hybridized and have linear geometry
how do you name alkynes
naming is analogous to alkenes but suffix is -yne not -ene
what are the dominant reactions for alkenes and alkynes
the dominant react for both alkenes and alkynes are addition reactions between one alkene/yne and another molecule like diatomic bromine.
Common additions include H2 (hydrogenation, H2O or hydrogen halides.
how do addition reactions work in alkenes / alkynes
One of the π bonds is replaced by two sigma bonds to the new atoms. Essentially a double bond goes to a single bond (or triple goes to double) and the two new atoms are bonded to the two carbons that previous held the double/triple bond.
what are aromatic hydrocarbons
Aromatic structures are formally related to benzene (C6H6)
they have delocalized π electrons which confer a special stability making them unreactive. they don’t regularly undergo addition reactions.
what are three common aromatic hydrocarbons
Naphthalone (basically 2 benzene rings, 1 only has 2 double bonds)
Arthracene (basically 3 benzene rings, 2 only have 2 double bonds)
Teluene (benzene ring with a methane group)
what are the three possible substituent relationships on a benzene ring
2 substituents on a benzene ring have 3 possible relationships:
if they are adjacent it is called “ortho” ie ortho-dinitrobenzene
if they have 1 carbon separating them it is called “meta” ie meta-dinitrobenzene
if they are on opposite ends it is called “para” ie para-dinitrobenzene
what are functional groups
the site of reactivity in an organic molecule is called a functional group
what are alcohols
R-O-H
ex methanol H3-C-O-H
-OH is a hydroxyl group, the oxygen is strongly and covalently bonded to both C and H
how do you name alcohols
Named from parent hydrocarbon; suffix changed to -ol
longest chain of carbon is numbered from end closest to hydroxyl group, number designates which carbon the hydroxyl group is attached to.
what are ethers
R-O-R’
ex methoxy methane H3-C-O-C-H3
relatively unreactive used as solvents
what are amines
organic bases with the general formula NRR’R”,
Nitrogen atom attached to 3 other groups
how do you name amines
named based on groups, then ending in amine
ex trimethylamine (CH3)3-N
how do you name ethers
shorter chain listed with suffix “-oxy” then linger carbon chain second
relatively unreactive used as solvents
what are aldehydes
R- C=O -H or R-CHO
chain attached to carbon of carboxyl group, hydrogen attach to same carbon
how do you name aldehydes
start numbering from aldehyde end, position not specified as it is always 1
ends in “-al” ex athanal
what are ketones
R-C=O -R’ or R-COR’
have two carbon (or chains) attached to the carbonyl carbon
how do you name ketones
ends in “-one” ex Propanone
chain numbered from end closest to carbon group
what are carboxylic acids
-C=O -O-H or R-COOH
carbon (chain) attached to carbonyl group, -OH attached to carbonyl carbon
weak organic acids
in acid base reactions with them the end hydrogen pops off
how do you name carboxylic acids
start numbering from acid end (position not specified)
(carbon chain)_”oic acid”
what are esters
R-C=O -O-R’ or R-COOR’
can be prepared by condensation reactions involving a carboxylic acid and an alcohol; the products are the ester and water:
R-COOH + HO-R’ —> R-COOR’ + H2O
how do you name esters
esters are named using the alcohol part first and then the acid part, ends in ”-oate”
ex methyl ethanoate
what are amides
composites of carbonyl and amine functionalities
R-C=O -N-R’ -R” or R-CONR’R”
in the above structure if R’ is H than it is the amide linkage, the key functional group in the structure of proteins
how do you name amides
when there are different options for the substitution patter, the prefix “N-” is used to indicate the group(s) bound to the nitrogen atom
ex N-Methylpropanamide
ends in “-amide”
what are chiral isomers
isomers that are mirror images of each other, but are non-superimposable are chiral
how can you tell is a molecule is chiral
you can test if a molecule is chiral by taking a mirror image and rotating it every way to see if it can be superimposed. Chiral molecules have mirror images that are distinct from the original
If a carbon atom has 4 different groups attached to it then it is a chiral centre and the entire molecule is chiral.
what are enantiomers
enantiomers = two isomeric molecules that are mirror images of each other: (if distinct)
they are a type of stereoisomer
“if one stereoisomer is “right-handed” the other is “left-handed”
also called optical isomers
the labels R- and S- are used to distinguish
how are enantiomers relevant to pharmaceuticals
a mixture of two Enantiomers in the same quantity is called a racemic mixture
Enantiomers generally have the same physical properties by ofter have different chemical properties when they interact with other chiral molecules.
Since many pharmaceutical are chiral; enantiomers have different biological activity
ex S-linalool is the scent of coriander while R-linalool is the scent of lavender since the olfactory receptors in humans have chiral groups
how are amides produced
Amides are produced by a condensation reaction between Carboxylic acids and amines
carboxylic acid + amine —> amides + water
