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88 Cards in this Set
- Front
- Back
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Describe the structure of NaCl |
Cubic Close Packed Chloride anion lattice Sodium cations filling all octahedral holes |
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Describe the Zinc Blende ZnS structure |
Cubic Close Packed Sulfide anion lattice Zinc cations filling half the tetrahedral holes |
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Describe the structure of NiAs |
Hexagonal Close Packed Nickel cation lattice Arsenic anions filling all octahedral holes |
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Describe the Wurtzite ZnS structure |
Hexagonal Close Packed Sulfide anion lattice Zinc cations filling half the tetrahedral holes |
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Describe the CsCl structure |
Chloride anion lattice Caesium cation in centre of cube |
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Give the equation for Magnetic Moment. |
Where n is the number of unpaired electrons. |
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In an octahedral splitting diagram, how many orbitals are stabilised in energy, and what is their label? Which orbitals are these? |
3, the dxy, dxz and dyz orbitals - t2g |
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Give the requirement for a system to be low spin. |
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Why are tetrahedral complexes always high spin? |
As the tetrahedral splitting energy is much smaller than that of octahedral, (4/9ths) |
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Give three factors that affect the octahedral splitting energy. |
1. Metal Charge - greater charge, greater Δo 2. Transition Series of the Metal - Δo increases down the group 3. Nature of the ligand - Δo increased by strong field ligands. |
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What is the Jahn-Teller Theorem? |
Any non-linear molecular system in a degenerate electronic state will be unstable and will distort to form a system of lower symmetry and energy to remove the degeneracy. |
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How is bond order calculated? |
Bond Order = number of electrons in bonding MOs minus the number of electrons in antibonding MOs, over 2 |
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Give the equation for the number of - total nodes - radial nodes - nodal planes |
- n-1 - n-l-1 - l |
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What are the four quantum numbers? |
n = principle quantum number l = angular momentum quantum number ml = magnetic quantum number ms = electron spink quantum number |
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What values can the principle quantum numbers take? |
- n can take integer values and defines the energy of the orbital - l can take values up to n-1 and describes the shape of the orbital - ml can take the values -l to +l - ms can take values -1/2 or +1/2 |
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What is the RDF? |
Radial Distribution Function - the likelihood of finding an electron at a certain distance from the nucleus. |
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Why is the 2s orbital more stable than the 2p orbital? |
The 3s orbital has a higher penetration closer to the nucleus into the inner layers of electrons, where it is held closely to the nucleus and can avoid the shielding effects of other electrons. |
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What is the effect of electronegativity on bond angle? |
Atoms with a greater electronegativity pull the electrons in the bond closer to themselves, decreasing electron density around the central atom so the bond repels others less - reduced bond angle. |
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Why are there discrepancies between experimental and theoretical lattice enthalpies? |
- Theoretical model is purely ionic with no covalency which would increase bond strength - Repulsions are approximated with Born exponents etc - Interatomic distances are estimated as separating ionic atoms is arbitrary so there will be errors |
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When are tetrahedral and octahedral holes formed? |
Tetrahedral - a triangle of close packed spheres with a sphere directly above the centre Octahedral - two triangles over each other in opposite directions |
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What are the issues with using radius ratio rules to predict packing structures? |
- Radii may not be correct - Nothing about covalency - No thermodynamics considered - Jahn-Teller distortions not considered - square planar stabilisation |
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What is the Pauli Principle? |
No two electrons in a given atom may have all four quantum numbers the same. |
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What is the Aufbau Principle? |
Atomic orbitals are filled with electrons starting from the lowest energy |
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What is Hund's Rule of Maximum Multiplicity? |
Electrons will arrange themselves so as to have as many parallel spins as possible |
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Why is the 4s orbital filled before the 3d? |
The 4s orbital is able to penetrate the lower energy orbitals closer to the nucleus, so the 3d is more effectively shielded from the nucleus. The two orbitals are very close in energy, so e-e repulsions can be significant in determining their order. |
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How is the order of filling determined for transition metals? |
For transition metal atoms in the gas phase - 4s filled before 3d For transition metals in compounds - 3d filled first |
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What are the two exceptions to the 3d/4s filling rules in Period 3? |
Cu: [Ar]4s13d10 Cr: [Ar]4s13d5 |
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Why does Zeff (effective nuclear charge) increase across a period? |
The atomic number Z increases (more protons), increasing nuclear charge. Electrons are added to the same shell - roughly the same distance from the nucleus. Shielding stays almost the same. Therefore the nuclear charge felt by the outer electrons increases. |
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What is the degree of shielding power of the orbitals and why? |
s > p > d > f Due to the different shapes of the orbitals |
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Why does atomic radius decrease across a period? |
- Increase in effective nuclear charge as Z increases and shielding stays the same - Greater degree of attraction between the positive nucleus and outer electrons - Electrons are held more closely to the central nucleus |
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Describe the trend in ionic radius across period 2. |
For positive ions - nuclear charge increases, positive charge increases, electrons feel increased Zeff, ion size decreases For negative ions - nuclear charge increases, negative charge decreases, electrons feel increased Zeff, ion size decreases Discontinuity as negative ions have much larger ionic radius than positive ions |
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Describe the trend in ionisation energy across Period 3. |
General trend is an increase as Zeff increases and atomic radius decreases. Deviations: - Al - outer electron removed from 3p orbital which is higher in energy than 3s - S - pair of electrons in 3p orbital experience mutual repulsion Both will readily lose outer electron so ionisation energy is lower than expected. |
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What is wave particle duality? |
The idea that all matter possesses characteristics of both waves (diffracted by a crystal lattice) and particles (mass) |
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Which orbital would n=3 l=2 ml=-2 correlate to? |
One of the 3d orbitals |
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What is Lewis Theory? |
A covalent bond is formed when 2 neighbouring atoms share an electron pair |
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What factors can distort molecular bond angles? |
- Lone pairs have a greater electron density closer to the nucleus and are thus more repulsive. As most repulsive interactions occur at 90', they will distribute themselves to minimise 90' repulsions
- Double bonds are also more repulsive than single bonds due to their higher electron density
- More electronegative atoms pull electron density away from the central atom - repulsion to other atoms decreases
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Why is electron promotion favourable? |
The energy taken to promote two electrons is easily compensated for by the energy gained from the formation of two extra bonds |
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What is isolobality? |
Structurally similar molecular fragments are described as isolobal. |
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Give the three interaction criteria for the LCAO approach? |
- the energies of the AOs must be similar - the symmetries of the AOs must be compatible - the overlap between the AOs must be significant |
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What is the a) HOMO b) LUMO c) SOMO |
a) the Highest Occupied Molecular Orbital b) the Lowest Unoccupied Molecular Orbital c) a Singularly Occupied Molecular Orbital |
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What are paramagnetic materials? What are diamagnetic materials? |
Paramagnetic materials have unpaired electrons and are attracted into a magnetic field Diamagnetic materials have only paired electrons and are repelled by a magnetic field |
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What is the sigma pi crossover and when does it occur? |
The σ2s and π2pz are very similar to the left of the periodic table and have the same symmetry so there can be secondary mixing of these orbitals. σ2s higher than π2pz. As we move to the right, there orbitals get further apart in energy - no overlap so π2pz is higher than σ2s. |
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What is the consequence of the different energies of the atomic orbitals in heteronuclear diatomic molecules? |
The MO will have more of the character of the AO it is closest in energy to. |
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Give the properties of a metal. |
- Electric and heat conductor - Malleable - Ductile - Lustrous - Can form alloys - Form basic oxides |
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Why do electronegative (non-metal) atoms form acidic oxides? |
The electronegative element pulls electron density towards itself, giving a build up of negative charge on the E and positive charge on the H. A proton is easily lost - acidic. |
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Why do electropositive (metal) atoms form basic oxides? |
Electropositive element pushes electron density away, giving a build up of positive charge on the E and negative charge on the OH. OH- easily lost - basic. |
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What is hydrolysis? |
The reversible loss of H+ from an aqua species. |
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What is the inert pair effect? |
As you go down the groups, there is an increasing tendency for the ns2 electrons to be left out of bonding. - The energy required to promote these electrons increases - The atoms get larger and their bonds get weaker - The energy of promotion is not compensated for by the energy gained from bond formation. |
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Why do favoured oxidation states vary by ±2? |
These ions will contain no unpaired electrons or radicals. Radicals are uncommon in the s and p block. |
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What is bond energy? |
The amount of energy required to break a bond into neutral atoms (for gaseous species) |
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Why do homonuclear single bond energies decrease down groups? |
The bonds get weaker as: - radii increase - orbitals are larger and more diffuse - poorer overlap |
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Why are N-N, O-O and F-F bond energies particularly weak, against the trend? |
They are small atoms, and therefore there is repulsion between adjacent lone pairs. |
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Are heteronuclear bonds generally weaker or stronger than homonuclear bonds? |
Stronger due to a greater difference in electronegativity |
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Why is the C-F bond stronger than the C-Cl bond? |
The size of the halogen atom is increasing, which leads to poorer orbital overlap and so weaker bonds. |
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Why is multiple bonding common in the first row of the p-block, but not in other rows? |
As the size of the atoms increases, there is poorer p-orbital overlap, and weaker π bonds. Nitrogen - 1 N≡N bond is stronger than 3 N-N Phosphorus - 2 P-P bonds are stronger than 1 P=P |
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What is catenation? |
The formation of single bonds between atoms of the same element type as π bonds would be weak, so multiple single bonds are favoured. |
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How can some molecules disobey the octet rule, according to Valence Bond Theory? |
The central atom may be able to use its empty d orbitals to form sp3d2 hybrid orbitals as they are not too much higher in energy. This is called hypervalence. |
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Why are alkanes kinetically stable in oxygen, but silanes are not? |
Si has accessible 3d orbitals, not too much higher in energy than the 3p orbitals which allow attack by oxygen. There is less steric hindrance around the Si as it is a larger atom. |
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How can H3PO4 form a P=O double bond when the P is sp3 tetrahedral? |
A π orbital is formed from backbonding of the Oxygen's p-orbital lone pair to an empty Phosphorus d-orbital. |
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What evidence do we have that π backbonding exists? |
When comparing Me3NO and Et3PO, we would expect the P-O bond to be the most polar due to the larger difference in electronegativity. The N-O bond is actually the most polar as the N donates a lone pair (dative) and π backbonding from O-P shortens the P-O bond and reduces charge separation. N(CH3)3 has trigonal pyramidal geometry N(SiH3)3 has trigonal planar geometry as this allows the N's p-orbital to overlap with the empty Si d-orbital. |
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Why is F2 highly reactive? |
Usually - general trend that bonds get weaker as atoms get larger and further apart F atoms very small and therefore the lone pair-lone pair repulsion weakens the bond F is the most electronegative atom and so will form very strong bonds with other elements - heteronuclear bonds are stronger than homonuclear. Reaction of F2 very thermodynamically reactive. |
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Why are boron trihalides monomeric, but other group 13 trihalides dimeric? |
Group 13 trihalides are electron deficient. As Boron is small its empty p-orbital can overlap with the halogen's p-orbital's lone pair to form a π backbond and provide stabilisation. Other group 13 trihalides dimerize to get 8 electrons and adopt tetrahderal geometry |
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What are the three possible sources of colour in transition metal complexes? |
- 'd-d' transitions as electrons move between d-orbitals - L-->M charge transfer - M-->L charge transfer |
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Why does the range of oxidation states in TMs increase towards the centre of the d-block? |
Across period: - Towards left all outer electrons easily lost - 3d orbitals become more stable (lower in E) - 3d acts more like core electrons and less like valence electrons - less likely to bond - The Ea to reach high oxidation states would be too high |
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Label the different parts of --> [ML]X |
M - Transition metal cation L - Inner sphere ligand (anion, cation or neutral) X - Outer sphere ligand anion |
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What are the two ways in which bidentate ligands may bind? What determines which is prefered? |
1. Chelating mode - when both donor sites of a bidentate ligand bind to the same metal centre. Preferred when a stable 5/6 membered ring formed 2. Bridging mode - when the donor sites of the ligand bind to different metal centres. Preferred when an unstable 4 membered ring would be formed by chelation |
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What geometry do coordination number 5 complexes take? |
Trigonal Bipyramid or Square Planar - however there is a marginal energy difference between the two so they can easily interconvert through the Berry Pseudo Rotation Mechanism - usual geometry is between the two. Each use different d-orbitals to form the sp3d different shapes. |
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What geometry do coordination number 6 complexes take? What type of geometric isomerism can octahedral complexes exhibit? |
Octahedral or Trigonal Prism - both use different d-orbitals to form the different sp3d2 shapes. Cis/trans for MX2L4 Mer/fac for MX3L3 |
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What are the drawbacks of Crystal Field Theory? |
It is a purely ionic model with no overlap/covalency of ligand and metal orbitals considered.
Only the metals' d-orbitals are considered. |
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Why is Tetrahedral Splitting Energy less than Octahedral Splitting Energy? |
- 4 ligands rather than 6 - smaller effect - The ligands do not point at any of the orbitals directly |
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What are high and low spin complexes? |
High spin complexes maximise the number of electrons with parallel spins Low spin complexes maximise the number of electrons in the lower set of orbitals |
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Put these ligands in order of weak to strong field CN-, NO2-, CO, NH3, H2O |
H2O < NH3 < NO2-, < CN- < CO |
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Why does Boron Trichloride not dimerize as Aluminium Trichloride does? |
Boron is small Effective overlap of empty p orbital with Cl's lone pair in a p-orbital - π backbond formed This provides stabilisation (octet satisfied) and shortens the bond Another Cl atom would not fit around the B atom |
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Why do d8 complexes prefer to be square planar rather than octahedral or tetragonally distorted? |
The crystal field splitting is high, so a large stabilisation results from filling only the lowest four d-orbitals |
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Why do lattice enthalpies not follow the expected trend based on size (radii decrease so should expect an increase in exothermicity. |
They only match the expected when CFSE is 0. A greater CFSE results in a greater deviation as there is increased stability so lattice enthalpy is more exothermic. |
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Why do stepwise stability constants decrease? |
Statistical reasons - gets harder to substitute when there are fewer ligands to substitute. First - 1/6 Second - 1/5 Third - 1/4 |
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Why are there poorly defined values for logK5 and LogK6 for an octahedral complex? |
The fifth and sixth bonds are very weak due to the Jahn Teller effect - therefore it is difficult to obtain meaningful data for coordination at these sites. |
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Where are tetragonal distortions more significant? |
More significant in the eg level rather than the t2g level as the ligands point directly at these orbitals |
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A thermodynamically favourable process would require? |
ΔG ≤ 0 E > 0 K > 1 |
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What is logB3? |
The overall stability constant for the substitution of the first three ligands (sum of the log of the stepwise stability constants) logK1+logK2+logK3 |
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What is Lattice Enthalpy (U)? A positive U value indicates... |
The amount of energy required to break up a solid and form and gaseous ions. A stable lattice |
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What is the Ksp of AgCl(s)? Why can the [AgCl] be ignored? |
Solubility Product Ksp = [Ag+][Cl-] AgCl is a solid so the [AgCl] is 1 (not going to change) |
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What is the common ion effect? |
The common ion effect is responsible for the reduction in the solubility of an ionic precipitate when a soluble compound containing one of the ions of the precipitate is added to the solution in equilibrium with the precipitate. |
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Why are back titrations sometimes necessary? |
- If excess is required for a complete reaction - If the endpoint of the first titration is unclear |
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What is a solid solution? |
The random distribution of one element in another. |
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What are substitutional and interstitial alloys?
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Substitutional - Atoms of one solute metal randomly occupy sites in the solvent metal lattice. Must have similar metal radii and electropositivities. Interstitial - Some of the holes between the metals are occupied by another element |
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Why do metals not shatter? |
The delocalised electrons leas to non-directional bonding which is uniform in all directions. Therefore its layers can be disruptive without losing attraction - so they only deform |
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How can the accuracy and precision of gravimetric analysis be improved? |
- Use an appropriate weighing form - Heat to a constant weight in a dessicator without touching - Increase the size and filterability - Digestion (redissolve and reprecipitate) - Precipitate from homogenous solution which generates the product slowly and in situe |
