Mr Joel Yr 12 Flashcards
(93 cards)
1
Q
What are structural isomers?
A
Compounds with the same molecular formula but different structures and properties
2
Q
What different suffix’s are for different functional groups?
A
Alcohol=_ol, Ketone=_one, Alkane=_ane,, Alkene=_ene, Carboxylic Acid=_noic acid, Aldehyde=_al, Nitrile/Cyanide=_nitrile, Ester=_oate
3
Q
What is the process of naming a compound?
A
Name all branches as a prefix, numbering them in relation to where the functional group is. The name the number of carbon atoms and finally choose the prefix for the corresponding functional group, numbering where it is when it is not on C1
4
Q
What is skeletal formula?
A
Shows the bonds of the carbon skeleton only with any functional groups
5
Q
How do you draw skeletal formula?
A
Each end of a line represents a CH3, or C atom, so draw the right number of line (eg, butane 3 lines) and then add any functional groups/branches to the right C.
6
Q
How do you work out the bond angles of a molecule?
A
- Count the areas of electron density (double bonds=1 area) 2. Count the number of areas that are lone pairs of electrons 3. -2.5 degrees per lone pair
7
Q
What are the different molecule shapes, and what are their bond angles?
A
2 areas of ED= Linear shape,180* 3 areas of ED= Trigonal planar arrangement,120* 4 areas of ED= Tetrahedral shape,109.5* (note, is not a flat molecule) 6 areas of ED= Octahedral shape,90* (note, not flat, akin to a 3D diamond in shape)
8
Q
What shape do the molecules become if one area of ED is a lone pair?
A
1 lone pair= Pyramidal (-2.5) 2 lone pairs= Bent/Non-linear (-5)
9
Q
What is the octet rule?
A
Atoms tend to gain, lose or share electrons in order to have a full set of valance/outer electrons, but cannot always do so.
10
Q
What is an alkyl group?
A
Everything not in the functional group of the molecule
11
Q
What is electronegativity?
A
The tendency of an atom to attract electrons in a covalent bond. Therefore the greater the electronegativity, the more it will attract the bonding pair
12
Q
What is electron shielding?
A
Inner electrons block the pull of the nucleus on outer electrons due to them having the same charge
13
Q
What is the Pauling scale?
A
It is a scale for electronegativity that states that the most electronegative elements are 1. F, 2. O, 3. Cl and 4. N
14
Q
What is a dipole?
A
An imbalance of charge in a covalently bonded molecule that is created due to one of the atoms being more electronegative than the other, like HCl. The strength of the dipole changes depending on how significant the difference is.
15
Q
What does a dipole create?
A
A polar molecule where the more electronegative attracts the bonding electron pair more than the other atom, giving it a δ - charge and the other atom a δ + charge (H2O)
16
Q
What indicates that a molecule is Polar?
A
- If it is Asymmetrical
- If it contains a very electronegative atom (F,O…) so therefore a strong dipole
- May have lone pairs of electrons
17
Q
What are the 3 different types of molecular forces?
A
- London forces/Induced dipole-dipole forces (weakest)
- Permanent dipole-dipole forces (medium strength)
- Hydrogen bonding (strongest)
18
Q
How can a substance containing induced dipole-dipole forces have a higher boiling point than one containing hydrogen bonds?
A
Because the strength of induced dipole forces can be increased when there are more electrons that randomly move, as well as the amount of shells an atom has, and therefore the more space an electron can randomly move around
19
Q
What are London forces?
A
Weak intermolecular forces that occur because electrons randomly move between shells. Sometimes this can cause an imbalance of charge on one side creating an induced dipole. This can then cause a dipole in the molecule adjacent to it and then a force of attraction between them. These forces can disappear very quickly
20
Q
What is permanent dipole-dipole intermolecular forces?
A
Molecules that contain a permanent dipole, like HCl, due to one atom being very electronegative. This allows the δ- of one polar molecule, say HCl, to interact with the δ+ of another polar molecule, e.g. another HCl. These intermolecular forces are generally stronger than London forces as the dipole is always there, not instantaneous
21
Q
What is a hydrogen bond?
A
Hydrogen bonds are intermolecular forces between atoms that contain an H covalently bonded to either an O, F or N. This is because these atoms are very electronegative, so create strong dipoles. Substances that contain hydrogen bonding also have to contain a lone pair of electrons, further strengthening the dipole. The forces themselves are therefore the electrostatic interactions between the δ- and the δ+ of 2 different molecules
22
Q
What is a sub-shell?
A
A group of orbitals of the same type within a shell
23
Q
What is an orbital?
A
A region in an atom where there is a high probability of finding electrons, and can hold up to 2 electrons with opposite spin
24
Q
What shapes are the orbitals?
A
-s-orbital= spherical
-p-orbital= dumbbell-like
-d-orbital= shaped like a 4 leaf clover
25
How many electrons can each periodic table block hold?
S-block= can hold max 2 e^-
P-block= can hold max 6e^-
D-block/transition metals= can hold max 10e^-
26
How do you write out an electron configuration?
1. Read across the periods, so it will always start with 1s^2 (1st shell, s-subshell containing H and He, 2 possible electrons held)
2. Continue down the periods, adding the p-subshells then the d-subshells
3. Count the d-subshells as -1 shell than the others (e.g. 4s^2, 3d^10,4p^6)
27
Why is the d-subshell always -1?
Because when the 4s sub shell is filled it reaches a more stable energy level than the 3d subshell, so it is always at a lower shell than the other subshells listed
28
What does [Ar] mean?
When listing an electron configuration, only list the electron subshells after the element in the brackets, which will always be a noble gas
29
How many electrons can an orbital hold?
2 electrons with opposite spins
30
How do you draw an electron configuration?
Electrons tend not to pair unless truly necessary, one electron will fill up each sub-shell before pairing up.
31
How many orbitals and sub shells do the first 3 shells have?
1st shell: 1s sub-shell, 1s orbital
2nd shell: 2s + 2p sub-shells, 1s + 3p orbitals
3rd shell: 3s + 3p + 3d sub-shells, 1s + 3p + 5d orbitals
32
In the case of Chromium (Cr) and Copper (Cu), how are their electron configurations different to the convention?
Chromium: The 4s and the 3d subshells are counted as one whole subshell, so there will be six electrons in each orbital before the electrons start pairing, e.g., [Ar] 4s^1 3d^5, not [Ar] 4s^2 3d^4
Copper: The 3d subshell fills entirely up before the 4s subshell, e.g., [Ar] 4s^1 3d^10, not [Ar] 4s^2 3d^9
33
What is the shape and bond angles of an alkane?
Alkanes always have a tetrahedral shape, due to each C having 4 areas of electron density around it, with a bond angle of 109.5*.
34
Why are alkanes described as saturated?
Alkanes are saturated as they contain only single σ bonds (single covalent bonds).
35
What is the orbital overlap model?
States that a bond forms when atoms are arranged so that their outer atomic orbitals overlap, forming a new shared orbital and therefore a σ bond. The more the orbitals overlap the stronger the bond.
36
How does covalent bonding work?
Due to the high density of electrons in the shared orbital of a σ bond, the nuclei impose an electrostatic force of attraction on the negative electrons, and therefore it is this attraction that keeps a bond from breaking.
37
How does a σ bond compare with π bonds?
σ bonds are the strongest type of covalent bonds, and allow rotation of the atoms involved in the bond as the orbitals will always overlap, whereas pi bonds don't allow atom rotation.
38
Why are alkanes unreactive?
-Because high bond enthalpy of σ bonds
-Very low polarity of the σ bonds present
39
How does the boiling point of alkanes vary and why?
It depends on the shape and length of the molecule. This is because alkanes are held together with London forces due to its non-polarity. Therefore the longer the molecule the larger its surface area, and the area of electron contact is larger as more e- are available to interact with, and so the London forces are stronger, which causes the BP to be higher. Branched molecules also have a lower BP because the shape causes it to have less e- contact and therefore weaker London forces.
40
What is an example of the complete combustion of an alkane?
C3H8 + 5O2 - 2CO2 + 4H2O Those products are a constant of the complete combustion of alkanes. Complete combustion occurs between gases so solid alkanes must be vapourised first.
41
What is an example of the incomplete combustion of an alkane?
2CH4 + 3O2 - 2CO + 4H2O Those products are a constant of the incomplete combustion of alkanes.
42
Why are alkanes used as fuels?
Because alkane combustion is highly exothermic, so releases more energy on the formation of bonds than it took to break the original bonds. Therefore longer chain alkanes release more energy than shorter alkanes (the latter being more volatile), and so the former is used for fuels needed for high energy engines, e.g., diesel in trucks.
43
Why is carbon monoxide dangerous?
CO has a high affinity for haemoglobin and will "bump off" the oxygen that should bind there. When carboxyhaemoglobin forms and travels to the tissues, the tissues will be hypoxic because less oxygen has been carried to the tissue. Therefore anything that burns alkanes must be properly ventilated, and a CO detector should be present.
44
What is a radical?
Atoms or molecules with a single unpaired electron. It is represented with a dot above the element, e.g. Cl*.
45
What is radical substitution?
A type of substitution reaction mechanism in which a radical replaces a different atom or group of atoms. The main 2 types are homolytic fission and heterolytic fission.
46
What is homolytic fission?
It refers to the breaking of a covalent bond in which each atom leaves with 1 electron from the pair in the initial covalent bond. (use half arrowheads)
47
What is heterolytic fission?
It refers to the breaking of a covalent bond in which one atom takes both of the electrons in the initially bonded pair. The more electronegative atom will take the pair. (use full arrowheads)
48
What are haloalkanes?
Alkanes with one or more halogen atoms bonded to a carbon in place of a hydrogen.
49
How are haloalkanes formed?
They can be formed by putting an alkane and halogen mixture under UV light (to provide energy), causing radical substitution to occur and creating a mixture of different haloalkanes. It has 3 main steps, Initiation, propagation and termination.
50
What happens in the initiation step of radical substitution?
A diatomic halogen molecule via homolytic fission to form halogen radicals. The UV light provides energy and is represented in the reaction as hv.
51
What happens in the propagation step of radical substitution?
1. The chlorine free radical takes a hydrogen atom from methane to form hydrogen chloride, a stable compound. This leaves a methyl free radical.
Cl∙ + CH₄ → CH₃∙ + HCl
2. The methyl free radical is also very reactive and reacts with a chlorine molecule. This produces another chlorine free radical and a molecule of chloromethane (a stable compound). The Cl∙ radical will then react with more methane and so on until one becomes the limiting factor.
CH₃∙ + Cl₂ → CH₃Cl + Cl∙
What happens in the termination step of radical substitution?
2 free radicals react to form a covalent bond : 2Cl* > Cl2 2CH3* > C2H6 Cl* + CH3* > CH3Cl
52
Why are alkenes described as unsaturated?
Because they contain a C=C double bond.
53
What are π bonds?
π bonds are formed by an overlap between the outer p-orbitals of two separate atoms. It forms at 90* to a σ bonds, which are overlaps of the s-orbitals, and resulting in 2 shared orbital areas above and below the σ bond. This is called being above and below the plane and causes them to be much weaker than σ bonds.
54
What are some properties of alkenes?
-Insoluble
-Boiling points increase with chain length
-Alkenes have a lower boiling point than their equivalent alkane
-Can exhibit E-Z isomerism
55
What is the area between the p-orbitals described as in a π bond?
Has a rich electron density
56
What is stereoisomerism?
It is a type of isomerism that occurs in compounds with the same structural formula but a different arrangement of atoms in space. This type of isomerism occurs in alkenes as the π bond restricts the rotation of the molecule. It can be classed as either E or Z isomerism.
57
What is cis-trans isomerism?
A type of E/Z isomerism in which two of the groups or atoms attached to opposing C in the C=C in alkenes are the same. To find out what type of isomer it is, find the identical groups or atoms on both C's, and work out if they are opposite to each other or on the same side. If they are opposite, it is a trans isomer and if they are on the same side it is a cis isomer.
58
What is E/Z isomerism?
A type of stereoisomerism that only occurs when a π bond is present and the C's in the π bond are bonded to different atoms or groups.
59
How are the E and Z isomers decided? (CIP)
1.Split the alkene in half, splitting the double bond
2.Look at the LC and look at what it is immediately bonded to, and using the atomic number, work out the group with the highest priority, which will be the atom with the highest atomic number.
3.If the LC is bonded to the same atom, look at al, the atoms that that atom is bonded to, add up all the atomic numbers, compare, and carry on until one has a bigger total and so is of a higher priority. If there is a double bond count the bonded atom twice.
4.Repeat on the RC
5.If the priority groups are opposite it is an E isomer and if they are on the same side it is a Z isomer
60
What are electrophiles?
Species that have a partial charge, either from an instantaneous or permanent dipole. This allows the rich electron density of C=C bond to be attracted to the δ+ of the electrophile, as the π bond is less under the influence of the nuclei than the σ bond.
61
What is the process of electrophilic addition reactions of alkenes?
1. The π bond is an area of rich electron density, so is attracted to the δ+ of the electrophile
2. An electrophile is formed when a dipole is created
3. The π bond is attracted to the δ+ atom in the electrophile, creating a bond with the δ+ atom
4. This forces the electrophile to split via heterolytic fission, causing the now separated δ- atom in the electrophile to form a separate - charged ion/anion
5. An intermediate is formed with the other C from the now broken π bond, which was broken via heterolytic fission, causing it to become a + carbocation, allowing it to form a bond
6. The anion from the electrophile forms a dative covalent bond with the carbocation
62
What is Markovnikov's rule?
When a compound containing H reacts via an addition reaction with an asymmetrical alkene, the H will bond with the carbon atom in the C=C that is bonded to the most hydrogen's already.
63
What is addition polymerisation, and what is the process?
-It is the process through which an unsaturated (containing a π bond) hydrocarbon, eg and alkene, links together with other unsaturated hydrocarbon molecules (monomers) to form a long saturated hydrocarbon chain (polymer)
-The π bond splits via homolytic fission to form 2 temporary C radicals
-The C radicals then react with other monomer molecules to form a polymer
-This can then be drawn as a repeat unit
64
What is a repeat unit?
A method of drawing a polymer that shows one monomer unit with large square brackets around it ([]) as well as an n to represent the number of monomer units present in the polymer.
65
What are alcohols?
Saturated hydrocarbon molecules that contain a hydroxyl (-OH) group as a functional group.
66
How does the BP of alcohols change as chain length changes? How does this compare with the BP of alkanes?
- The BP of alcohol increases as chain length increases
-This is because as the hydrocarbon chain length increases, there are more points of surface contact between the molecule, and therefore more areas in which London forces can occur, increasing the BP
-The BP of alcohols is also more than that of their respective alkane, as the hydroxyl (-OH) group means that hydrogen bonding will occur between alcohol molecules
-This strengthens the forces of attraction between alcohol molecules and increases the BP, as more energy is required to overcome the both the London forces and the Hydrogen bonds
67
Are alcohols soluble and how does it change with chain length?
-Alcohol molecules are soluble due to the hydroxyl group allowing them to form hydrogen bonds with water molecules
-The solubility of alcohols also decreases as chain length increases
-This is due to the fact that the effect that the hydroxyl (-OH) group and the hydrogen bonding that occurs because of it, decreases as the molecule length increases, as the alkyl group is non-polar
68
How is ethanol produced industrially?
Via the hydration of ethanol. This involves the electrophilic addition of ethene and vapourised H2O (steam). This involves the formation of a hydroxide anion and a carbo cation.
H2C=CH2 (g) + H2O (g) --H3 PO4 (aq) -> H3C-CH2 OH (l)
Conditions:
-Phosphoric acid catalyst
-Moderate pressure
-High temperature
-Operated continuously - Atom economy=100% as only 1 product
69
What are primary, secondary and tertiary alcohols?
Primary = The C bonded to the hydroxyl group is bonded to 1 or no adjacent C atoms
Secondary = The C bonded to the hydroxyl group is bonded to 2 adjacent C atoms
Tertiary = The C bonded to the hydroxyl group is bonded to 3 adjacent C atoms
70
What oxidising agent is used for the oxidation of alcohols, and how does it indicate the end of the reaction?
-The agent used is acidified dichromate (VI) ions, written as [H+/Cr2O72-]. This is potassium dichromate (VI) dissolved in concentrated sulphuric acid (H2SO4). This can be represented as [O].
-The solution of the [O] and the alcohol will be orange due to the presence of orange Cr2O72- ions. As the reaction continues, these ions will be reduced, as the alcohol is oxidised, to form green Cr3+ ions (Cr6+-> Cr3+), causing the solution to become green.
71
What are the products of the oxidation of certain alcohols?
1* alcohols -- Distillation with [O] --> Aldehyde
1* alcohols -- Reflux reaction with [O] --> Carboxylic acid
2* alcohols -- Reflux reaction with [O] --> Ketone
3* alcohols resist oxidation due to the C-OH bond being too stable.
*Reflux reactions are a longer process than distillation
72
What happens when an alcohol is reacted in either a dehydration or a substitution reaction?
Dehydration:
-An alcohol is reacted with an acid
-This forms an alkene and water
Substitution:
-Any alcohol can be reacted with a more reactive halide to form a haloalkane
-This is when an alcohol was is reacted with acidified sodium halide
73
How is an alcohol distilled to form an aldehyde?
-Partial oxidation of 1* alcohols to create aldehydes occurs by distilling off the aldehyde product before it can be oxidised again
CH3OH + [O] -> HCHO + H2O
-This is done by using the usual apparatus for the distillation of a liquid
74
How is an alcohol refluxed to form a carboxylic acid?
-Refluxing the reaction mixture ensures the aldehyde product doesn't escape and allows it to continue to be oxidised
CH3OH + [O] -> HCHO + H2O
HCHO + [O] -> HCOOH
-The method of this reaction involves putting the Liebig condenser in the top of the volumetric flask so that any gaseous aldehyde condenses before escaping
75
What is a nucleophile?
A species that has a lone pair of electrons with which it can form a dative covalent bond by donating them to a C atom.
Examples,
-Hydroxide ions, :OH^-
-Ammonia, :NH3
-Cyanide ion, :CN^-
76
What is an electron deficient centre?
The carbon to halogen bond contains a dipole due to the electronegativity of the halide. Because the C is very positive, nucleophiles are attracted to this, so the C atom is called an e^- deficient centre due to its positive charge.
77
What is the process of nucleophilic substitution?
1. The C to halogen bon breaks via heterolytic fission, with the halide receiving the e^-
2. The nucleophile forms a bond with the now positive C atom, donating its e^- to the e^- deficient centre
3. The nucleophile hydrocarbon and a halide ion are formed as products
-An easy way of conducting this with OH^- ions is by using an alkali
78
How do the reactivity of the carbon halogen bonds change down the group?
It increases down the group. This is because of the decreasing bond enthalpy down the group, due to the valence e^-'s being further from the nucleus. This means that the C-I bond has a lower bond enthalpy than the C-Cl bond, and so is more reactive as it will break more readily.
79
What is the ozone layer, and how is it created?
-A thin layer of O3 (ozone) molecules that reflect the majority of harmful UV away from the earth's surface
-Forms when an oxygen molecule create a dative covalent bond with an oxygen radical
O2 -UV-> 2O*
O*+ O2 -> O3
-Overall the equation is O3 ⇌ O2 + O*
80
How is the ozone layer broken down by CFC's (chlorofluorocarbon's) ?
-Via free radical substitution, as UV light splits the C-Cl bond producing a very reactive chlorine radical
-CFC's now banned, but were used for their inertness on the earths surface, and they are non-toxic
-Happens to all Cl containing compounds under UV
Initiation = CF3Cl -UV-> Cl* + *CF3
Propagation = Cl* + O3 -> *OCl + O2
*OCl + O* -> Cl* +O2
-Process then repeats as chlorine radical is reproduced, and only terminates when 2 Cl* react to form Cl2
-Alternatives include HCFC's (hydrogen chlorofluorocarbon's) and HFC's (hydrogen fluorocarbon's)
81
What is the greenhouse gas effect and what gases can be part of this layer?
-A layer of gaseous molecules, mostly CH4 and H2O, that must contain a dipole
-When UV hits the earth's surface, it reflects, losing energy and becoming Infra-red
-This energy is then absorbed by the bonds in the gas molecules, causing the to become more energetic and transfer this kinetic energy (heat) to neighbouring molecules
-This heats up the atmosphere
82
What is IR spectroscopy?
-IR is shined at the sample
-The covalent bonds absorb IR at specific wavelengths
-IR vibrates at a specific frequency, meaning each bond vibrates differently and so the bonds/functional groups can be determined
-Produces a spectrum with peaks that go down from THE TOP of the spectrum
83
What is mass spectroscopy?
-Molecules are bombarded with e^- to break them into fragments
-These fragments pass an electro-magnetic field that accelerates them, shooting them down a tube to a detector
-This measures the time it takes for the fragment to reach the end and records it as a peak on the spectrum produced
-To work out the molecule present take the 1st significant peak from the 2nd, and the 2nd from the 3rd....
84
What are the peaks at the end of a mass spectrum?
-The last significant (in size) peak on the spectrum is the entire molecule so, so is the Mr of the molecule in question, and is called the M^+ peak
-The very small peak at the end is called the M+1 peak, and occurs due to there being some C13 present, so should be ignored
85
What is the test for carbonate ions?
-Carbonates react with acids to form CO2
-Add dilute nitric acid and if effervescence is produced, then a CO3^2- ion could be present
-To affirm this test, bubble the gas through lime water and if it turns cloudy the gas produced is CO2
Ionic equation = H^+ (aq) + OH^- (aq) -> H2O (l)
86
What is the test for sulphate ions?
-Most sulphates are soluble, but barium sulphate is insoluble
-When BaCl2 or Ba(NO3)2 is added to the solution, Ba^2+ ions will react with any sulphate ions to form a white BaSO4 precipitate
-This precipitate should be insoluble and sink to the bottom of the test tube
Ionic equation = Ba^2+ (aq) + SO4^2- (aq) -> BaSO4 (s)
87
What is the test for halide ions?
-Silver ions will react with halide ions to form different colour precipitates
-Therefore, AgNO3 is added and the colour precipitate is observed
Cl^- = white precipitate
Br^- = cream precipitate
I^- = yellow precipitate
Ionic equation = Ag^+ (aq) + X^- (aq) -> AgX (s)
-Ammonia can be used further confirm the ion present
-Cl = soluble in dilute NH3
-Br = insoluble in dilute NH3, soluble in concentrated NH3
-I = insoluble in all NH3
88
What is the test for ammonium ions?
-It will act as an acid when it is added to a compound with basic properties, eg, NaOH
-Will donate a proton to form NH3 gas, which is alkaline, so must be heated with the base until effervescence forms
-When damp red litmus paper is held above the solution, it will turn blue
Ionic equation = NH4^+ (aq) + OH^- (aq) -> NH3 (g) + H2O (l)
89
What is dynamic equilibrium?
-Dynamic equilibrium is when the rate of forward reaction and the rate of the backwards reaction are equal
-This occurs in a closed system, in which the concentrations of reactants and products remain constant
90
What is Le Chatelier's principle?
-The principle states that if a system is in equilibrium, and is subjected to an external change, the system will change to counteract the effect of the change.
91
What are the external changes, and how does the equilibria change to counteract these changes?
Concentration:
-If the reactant conc. is increased, equilibrium shifts to produce more products, so the equilibria shifts to the right
-If product conc. is increased, equilibrium shifts to the left, so more reactants produced
Pressure:
-When pressure is increased, equilibrium will shift to the side which has the fewest gas molecules present
-If pressure decreased, equilibrium shifts to the side that has the fewest gas molecules
Temperature:
-Increasing temperature makes the equilibrium shift in the direction that is most endothermic
-Can be determined using standard enthalpy change as exo=- value, endo=+ value
92
What is a catalyst, and how does it affect equilibrium?
-A catalyst is a substance that increases the rate of chemical reaction by lowering the activation energy and providing an alternative reaction pathway
-The presence of a catalyst will only alter the rate of reaction and no the equilibrium as it will increase the rate of forwards and backwards reaction equally
93
What is the equilibrium constant, what is the associated equation, and what are the rules pertaining to this constant?
The equilibrium constant, Kc, gives information about whether the position of equilibrium lies to the left or right of the reaction
Rules:
-If Kc is 1, then the position of equilibrium is half-way between the reactants and products
-If Kc is less than 1, then equilibrium lies to the left, towards the reactants
-If Kc is more than 1, then equilibrium lies to the right, towards the products
Kc=[C]^c[D]^d/[A]^a[B]^b
-The capital letters = the reacting compounds concentrations
-The lowercase letters = the number of moles of the compounds
