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Title: Inorganic Chemistry First Year
Description: Chemistry short notes on Inorganic topics dealt with in A level First Year of Sixth form. Main topics are: Atomic Structure, Mass Spectrometry, Orbitals, Radioactivity, Gas laws, Isomers, Bonding (very detailed), Shapes of molecules, Redox, Thermodynamics, and Equilibria.
Description: Chemistry short notes on Inorganic topics dealt with in A level First Year of Sixth form. Main topics are: Atomic Structure, Mass Spectrometry, Orbitals, Radioactivity, Gas laws, Isomers, Bonding (very detailed), Shapes of molecules, Redox, Thermodynamics, and Equilibria.
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Chemistry short notes
Atomic Structure
• Mass/Nucleon number - number of particles in an atom - protons + neutrons
• Relative atomic mass - mass of an atom compared to 1/12th of Carbon-12
• Purpose of neutrons? Protons are +ve so they would repel each other, neutrons added to keep
the nucleus intact
...
If large difference - nucleus is unstable and probably
radioactive
...
Mass Spectrometry
• Mass spectrometer - measures the m/e mass to charge ratio for a particle
...
Ionisation chamber
Pump evacuates mass spec to remove air particles
...
E- pass into ionisation chamber
...
5
...
1
...
3
...
6
...
7
...
8
...
• Uses: determine RAM of element; determine RMM of compound; identification of compounds;
forensic science investigations; determine between isotopes
...
• Bromine: 79-81 1:1 doublet & 172-174-176 1:2:1 triplet
Bohr Model
• E- contain a quantised (specific) amount of energy
...
• E- can be promoted from shell near nucleus (ground state) to
shell far (excited state) by heat/electricity
...
• Orbital - space where there is a 95% chance of finding an e-
Ionisation Energy
• 1st IE - the energy required to remove one mole of e- from one mole of a gaseous element
forming 1 mole of unipositive cations (kJmol-1) A (g) —> A+ (g) + e• 2nd IE - the energy change to remove the second electron from one mole of unipositive cations
to form one mole of gaseous dipositive cations A+ (g) —> A2+ (g) + e• Factors affecting the 1st ionisation energy:
1
...
2
...
3
...
IE decreases down the group, therefore reactivity dec
...
IE increases across period •
more e- on same shell and proton number is increasing
...
2,8,8,1)
Inc in values because
inner shells are closer
to the nucleus and so
they are more strongly
attracted when
compared to outer e-
...
• No of IE before large jump = no of e- in outer shell = group no (first divide —> if all similar then
subtract)
...
Orbitals
Shells:
•s-2
•p-6
• d - 10
• f - 14
^ Hund’s Multiplicity Rule - least repulsion
...
: less
reactive & slight
peaks observed in
the graph —>
Electronic Configuration of the Transition Metals
• When you reach 4th shell - OVERLAPPING - 4s orbital has a
lower energy than the 3d orbital
...
21 electrons - 21st e- is placed in the 3d subshell: (Ar)
4s2 3d1
• Since transition metals use d subshell —> d clock elements
...
• When forming ions - e- are first lost from the 4s subshell not 3d
...
• Detected by Photographic film, Geiger-Muller tube, Bubble chamber
...
• Neutron rich substances emit Beta particles: n —> p + e-
...
• Alpha decay occurs in heavy isotopes - He nucleus emitted
...
: nucleus remains intact
...
• Elements decay until they reach a proton: neutron ratio of roughly 1:1
• An alpha decay followed by 2 beta emissions is a very convenient way of producing a radioactive
isotope of the same element
...
• Chemical reactions - involves transfer or sharing of electrons
...
Rate at which decay occurs depends on the nature of the isotope
...
Larger the half life, the more stable it is
...
• GM tube - gaseous ionisation detector used for gamma, alpha, beta and x-rays
...
Geological dating
Reaction mechanisms - esterification reaction where radioactive oxygen is used to understand
how the carboxylic acid and alcohol interact
...
• When organism dies, it stops absorbing the radioactive isotope and immediately starts decaying
...
: measuring remaining C-14 in organism can tell you how long
ago it died
...
• Avogadro’s hypothesis - equal volumes of gases measured at the same volume and pressure
contain the same number of molecules
...
414dm3 @ s
...
p
...
414dm3 @ r
...
p
...
• Ideal gas equation: P1V1/T1 = P2V2/T2
• PV = nRT (P in Pa; V in m3; T in K; R = 8
...
• Liquid is weighed accurately in syringe & injected into the gas syringe (empty syringe weighed)
...
• Temp and atmospheric pressure in the steam jacket are noted
...
• Assumes that mols move randomly, occupy negligible volume, exert no pressure on each other &
have elastic collisions (assume that no energy is lost)
...
• Partial pressure of a gas in a mixture is the pressure a gas would exert should it be alone
...
• Diffusion - movement of 2 gases when they are mixed together
...
Isomers
Constitutional Isomers
Structural isomers which share the same molecular formula but the bond connections and/or their
order differs between different atoms/groups
...
1-chloropropane & 2-chloropropane
• Functional group isomers - totally different functional groups eg
...
• Diastereoisomers - isomers made since double bond doesn’t allow for rotation - cis (boat) & trans
(chair) cis more compact, trans higher s
...
: higher b
...
• Enantiomers - optical isomers: mirror images of each other - asymmetric carbon atom not
superimposable (like right hand and left hand) - totally identical properties except optical
properties
...
Bonding
Ionic (Electrovalent) bonding
•
•
•
•
•
•
Transfer of e- & formation of ions e
...
NaCl - Na+ + Cl-
...
Electrostatic attraction is the chemical bond in the compound
...
Metallic element + non-metallic element
...
Factors affecting the 1st ionisation energy
1
...
2
...
3
...
• Ionisation energy decreases down the group, therefore elements with a lower ionisation energy
are more reactive
...
This is because in the
2nd Group, there are 2 electrons in the outer shell, therefore more ionisation energy is required
to remove 2 electrons
...
e
...
• The 2nd ionisation energy is lower than the first in group 6, because since there are only 2
electrons, it is easier to loose the 2nd electron since there is repulsion between the 2 electrons
...
(Group 1 & 2)
• Electronegative: (cations) the tendency of an atom or molecule to attract electrons and thus form
bonds
...
Shielding effect increases down the group (as there
are more shells) but doesn’t change across the period, because the inner electrons are constant
...
• Electron affinity: (anions) the amount of energy released when an electron is added to a neutral
atom to form a negative ion
...
(Opposite of ionisation energy where
energy is needed to loose an electron - energy is released when gaining an electron)
...
However, electronegativity decreases down the group (due to shielding affect, weaker
force of attraction to nucleus)
...
• From left to right of the periodic table electropositivity decreases (more electrons in the same
shell so harder to lose) and electronegativity increases (more electrons in the same shell so
easier to gain an electron)
...
What is the difference between electron affinity and
electronegativity?
• Electron affinity is a measure of the energy released
...
• 1st Electron affinity: the energy released when one mole of gaseous atoms each acquire an
electron to form one mole of gaseous anions
...
This decrease in electron affinity corresponds to a parallel increase in the
shielding effect down the group
...
One
would expect Fluorine to have a
higher electron affinity than the
outer halogens because the
incoming electron is going to be
close to the nucleus
...
This implies that an
incoming electron will experience
more repulsion, decreasing the
overall electron affinity
...
• There is a stronger nuclear positive charge on the same electronic structure (an isoelectronic
series)
...
• Across a period, anionic size decreases due to increase in nuclear pull
...
Ionic Radii
• When ionic compounds solidify they from crystals
...
When removed becomes
anhydrous powder
...
• Anionic radius - radius of anion
...
• Isoelectronic - refers to ions/atoms with the same electronic configuration eg
...
• Crystal lattice made from a basic unit (unit cell) which is repeated throughout the structure
...
• Equal number of electrons but proton number is increasing —> inc in charge density - higher
tendency to form covalent compounds
...
: ionic
...
When bonding with Cl- it disrupts
the e- cloud of Cl
...
• Covalent vs Ionic —> depends on relative size and charge - charge density
...
2+ charge with smaller size
Mg>Ba
3D structure of ionic compounds
• NaCl - Face Centred Cubic Close Packing Lattice
• Consists from close-packed arrangement of anions, with the
smaller cations filling the octahedral holes
...
• Each F- has 4 Ca2+ ions tetrahedrally arranged around
it
...
• Large amount of energy must be supplied to make ions vibrate & eventually break off
...
• Brittle
• Crystals are hard but can be cleaved - split using a very sharp razor edge
...
• Repulsion results which fractures the crystal
...
When you apply force, metal will change shape as electron cloud
moves quickly to surround moved anions
...
• If you bend constantly - will heat up due to constant movie of the e- cloud
...
• Conduction of Electricity
• Only when molten or in solution
• When solid - ions held together in crystal - unable to move
...
• When molten/in solution ions are free to move and an electrical current can pass through
...
• Water has an uneven e- distribution - polar molecule
...
near the O atom rather than the H atom
...
• The new ion-solvent bonds formed results in a release of energy
which helps break down the strong electrostatic forces in the
crystal lattice
...
• Do not dissolve in organic solvents since these have weak molecular forces between them
which are not strong enough to penetrate the crystal lattice
...
g
...
: NaCl is more soluble - less shielding effect, so
more attracted to water molecule
...
Change in entropy will be so large that reaction still takes place
...
• When going up the group, charge density increases - decreasing atomic radius
...
g
...
• These have an electron efficient structure - don't have 8 e- around central atom
...
• They can have up to 10/12 e- in outer shell
...
• Hybridisation - convergence of 2 or more orbitals in space providing the vacancy for more e- to
be accommodated
...
When C and H bond
energy is released - some of which is used to move an electron from 2s to 2p in C - merge into
a sp3 orbital - energetically more stable
...
•
• E
...
PF5 has 10 e- around central atom & SF6 has 12 e-
...
• Van der Waals’ radius - half the distance in an atom which is not chemically bonded
...
Two kinds of Covalent Bond
• Sigma bond - When the orbitals from 2 atoms overlap along the line
drawn through 2 nuclei, a sigma bond forms
• E
...
2 s orbitals, a s & p orbital, or 2 p orbitals can overlap
• Pi bond - Sometimes, after a sigma bond has
formed between 2 atoms, the p orbitals of the
2 atoms also overlap above and below the line
drawn through the 2 nuclei and another bond
forms
...
• Degree of overlap in Pi is less than in sigma
...
• Species which provides this pair of e- must have a lone pair and is called the donor
...
• E
...
water bonds datively with a H+ to form hydroxonium ion
...
• AlCl3 can dimerise when cooled to form Al2Cl6
...
• Upon heating forms monomers again
...
g
...
• Electronegativity - ability of an element to attract bonded e- towards it in a covalent bond
...
g
...
The
centre of the -ve charge (due to e-) does not coincide with the centre of the +ve charge (due to
nucleus)
...
Molecule is slightly negative on the Cl atom
and slightly positive on the Hydrogen atom
...
• Symmetrical molecules have an even distribution of e- cloud and are said to be non-polar
...
Small radius enables the nucleus to exert larger effect and high positive charge will
attract e- cloud of neighbouring atoms towards it
...
• E
...
inc in polarisability Cl- < Br-
• A polar bond is an uneven distribution of the electron cloud in molecules whose atoms
are covalently bonded
...
• If the difference in electronegativity is:
• 0 = Pure covalent e
...
Cl2
• 1
...
g
...
3)
• Values suggest that there is no pure covalent/ionic compound
...
• Electronegativity values decrease down a group due to increasing atomic number and screening
which overcomes the increasing atomic number
...
• Small cation w/ high charge + large anion = covalent e
...
AlI3
• Small cation w/ low charge + large anion = ionic e
...
LiBr3
• Small cation w/ low charge + small anion w/ low charge = ionic & slightly covalent
...
g
...
• Large cation + large anion = cation won’t polarise anion - ionic e
...
BaCl2
• Shift of ionic character to covalent character from left to right across a period
...
Similarly the
difference in electronegativity between the oxide and the other element is also decreasing
...
• Dipole-Dipole interactions
• 2 polar molecules bonded - asymmetric distribution of e-
...
E
...
HCl and HBr
• Van der Waals forces
• Induced dipole - induced dipole interactions
...
g
...
a
...
• Strongest intermolecular bond
...
p
...
’s and m
...
t
...
• Substances which have H-bonds are extremely soluble in water
e
...
ammonia and alcohol
...
• E
...
When HCl reacts with H2O, the energy released overcomes the energy invested to break the
bond between HCl molecules
...
p
...
: inc in mol size down group
...
Group 5 - trend like Group 4 except NH3 - mostly H-bonds
...
p
...
Group 6 - same concept with H2O - extremely higher b
...
t
...
Group 7 - inc
...
B
...
t
...
• F —> dense e- cloud (small molecule) - difficult for another HF molecule to approach another strong repulsion
...
Dimerisation of Carboxylic acids
• Dimer - forms H-bonds with itself
...
• Benzene —> non-polar solvent, so ethnic acid would rather
bond with itself than interact with benzene
...
: weak acid
...
in water dec
...
• Solubility of longer chained acids decreases rapidly with size
...
The H-bonds are replaced with weaker Van der Waals
...
• Diamond
- Each C forms 4 bonds (sp3 hybridised) forming tetrahedral arrangement
...
- Virtually non-reactive
...
-
High m
...
t
...
p
...
Hard - tetrahedral shape can withstand pressures from all directions
...
• Graphite
- sp2 hybridisation
...
p
...
than diamond —> thermodynamics
...
- Delocalised electron
...
- High m
...
t
...
- Uses: Lubricant in heavy machinery, electrodes
during electrolysis
...
- Used as a catalyst to lower activation energy in nanotechnology
microchips; nano-engineering - medicine —> since inert
...
• Each Si-O bond is tetrahedrally distributed with each O atom bonded
to 2 Si atoms, and each Si bonded to 4 O atoms
...
p
...
• Structure also occurs in Quartz - m
...
t
...
Metallic bonding
• A cluster of metallic cations attracted to an electron cloud
...
• Strong
• Deformed without breaking
• Malleable (hammered)
• Ductile (worked into a wire)
• Shiny when freshly cut
• Good conductor of Heat and Electricity
• Brittle
• Metallic bond is a cluster of anions surrounded by a delocalised cloud which fills gaps between
anions
...
: no repulsion occurs & won’t break —> malleable
...
Inc in KE - can
overcome forces of attraction & break
...
• Metal absorbs the hear and transfers it into kinetic energy
...
• Good conductor of electricity
• Free e- cloud makes it electrically conductive
...
• As temperature inc, conductivity dec because the particle collisions in the lattice divert the efrom forward transport of charge (random motions of cations disrupts unidirectional electricity
flow) - concept of electric resistance of wire
...
• Light excites e- inside atoms - when go back to original shells they release a packet of energy
in the form of light
...
• Strength of metallic bond increases across a period, due to inc in no of delocalised electrons
...
Amphoteric Character of Al3+, Zn3+, Sn2+, Pb2+
- Can release H+ ions (Brønsted-Lowry Acid)
- Can accept H+ ions (Brønsted-Lowry Base)
• Must have a lone pair in structure
• Al3+ high charge density - surrounded by water —> hydration shell - attracting so many eweakening O-H bond in H2O until it breaks, releasing an H+ ion in water making solution acidic (
...
• pH dec
...
Shapes of Molecules
Valence Shell
Electron
Repulsion Theory
- count pairs of e-
Multiple bonds do
not allow for
rotation
...
Redox
• Common Oxidising Agents
• Oxygen
• Chlorine, Bromine, Iodine
• Manganate (VII) MnO4 in acid/alkaline solution
• Dichromate (VI) in acid solution
• Iron (III) salts
• Hydrogen ions
• Hydrogen peroxide (in the absence of another oxidising agent)
• Manganese (IV) Oxide MnO2 (in the presence of acid)
• Concentrated sulphuric acid
• Common Reducing Agents
• Metals
• Iron (II) salts
• Acidified potassium iodide
• Thiosulphate S2O3 2• Ethandioic acid C2O4
• Hydrogen sulphide and sulphides
• Sulphurous acid
• Hydrogen peroxide (in the presence of a strong oxidising agent)
• Hydrogen
• Carbon
• Carbon monoxide
Balancing Redox Equations
1
...
Use H2O to balance O
2
...
Use e- to balance charge
2
...
Same as above
2
...
• Disproportionation - element is oxidised and reduced in the same reaction
...
Potassium Manganate Titrations
• Used in titrations to determine unknown quality of reducing agents e
...
Fe 2+
• No indicator - when all MnO4 - has reacted solution turns pink to colourless (self indicating)
...
• MnO4- + 8H+ —> Mn2+ + 4H2O
• Fe2+ —> Fe3+ + e• MnO4 - + 8H+ + 5Fe2+ —> Mn2+ + 4H2O + 5Fe3+
Sodium Thiosulphate Titrations
•
•
•
•
•
•
Thiosulphate —> Tetrathionate
2S2O32- —> S4O6 + 2eStandardised using Iodine
...
2S2O32-(aq) + I2(aq) —> 2I-(aq) + S4O62-(aq)
Estimation of Chlorine
• Chlorine displaced iodine from iodides - iodine formed determined by titration against sodium
thiosulphate
...
no to all the atoms in the equation
...
no
...
no = dec in ox
...
Balance the other atoms by using the inspection method
-3 x 2 = -6
+2 x 3 = +6
Balancing: 1, 3, 2, 3
Thermodynamics
•
•
•
•
Study of energy changes
Heat content is known as enthalpy (H)
Bond breaking - energy needed (activation energy)
Bond forming - energy released
• 1st law - Energy can be changed from one form into the other, but it can neither be created nor
destroyed
...
• Entropy - chaos, without which the reaction would not take place
...
• Enthalpy of Formation △Hºf
• Heat absorbed when 1 mole of a substance is formed from its elements in their standard state
(r
...
p
...
Heat is
evolved and
...
More -ve = better fuel
• CH4 (g) + 2O2 (g) —> CO2 (g) + 2H2O (l)
• Lattice Enthalpy of △Hºa
• The enthalpy change when 1 mole of an ionic compound is formed from its gaseous ions
...
• Na (g) —> Na+(g) + e• Second Ionisation Energy △Hº2nd IE
• The enthalpy change when one mole of electrons is lost from a mole of unipositive ions
...
of mole of reactants as given in the
stoichiometric equation at 1atm
...
in a stated amount of
solvent
...
• Bond Dissociation Enthalpy of △HºBDE
• Enthalpy change when 1 mole of bonds are broken in the gaseous state
...
1
...
The temp is notes
...
2
...
Note the rise in temp
...
- In all thermochemical measurements, it is the usually practice to consult a cooling curve to
compensate for any heat losses, even though the cal used is highly insulated
...
3
...
Experiment to find enthalpy of combustion
•
•
•
•
•
Spirit burner contains fuel : weight after - weight before = mass of fuel burnt
Metal cal
...
Thermometer to measure change in temp
Draught shield to reduce heat losses
...
Hess’s Law
The final energy change for a reaction is the same, independent of the pathway
...
Born Haber cycle
—> application of Hess’s Law to enthalpy changes
which occur when an ionic compound is formed
...
Since standard bond enthalpies vary from one compound to
another, the use of average bond enthalpies gives only an approximate call for the standard
enthalpy of reaction calculated from them
Experimental methods are used to obtain enthalpies of reaction wherever possible
...
Rate of Forward reaction = Rate of Backwards reaction
Le Chatelier's Principle - If a dynamic equilibrium is disturbed by changing the conditions, the
position of equilibrium moves to counteract the change
...
The system counteracts the change you have made by absorbing the extra heat
...
The system counteracts the change you have made by producing more heat
...
Kc is temp dependant
If you dec pressure, system will oppose by increasing pressure, by breaking down the products
into original molecules
...
they are all
decreased, but NH3 more than others ; Kc is
unchanged ; Eq shifts to the right ; Both rates
dec
...
pressure - An inc in all conc
...
• Adding a noble gas (
...
: higher pressure) - Noble gas mol
...
: does not inc at a very fast rate
...
Reaction tries to
dec
...
: the reaction moves forwards
...
inc but N2 and H2 more than NH3 ; Kc is
unchanged ; The eq position moves to the left ; Both rates will be slower - since they are in a
bigger volume, less collisions
...
• Changing temperature - An inc
...
will favour the back reaction - Conc
...
of NH3 will dec
...
; Eq will shift to the left ; Both rates
will inc
Title: Inorganic Chemistry First Year
Description: Chemistry short notes on Inorganic topics dealt with in A level First Year of Sixth form. Main topics are: Atomic Structure, Mass Spectrometry, Orbitals, Radioactivity, Gas laws, Isomers, Bonding (very detailed), Shapes of molecules, Redox, Thermodynamics, and Equilibria.
Description: Chemistry short notes on Inorganic topics dealt with in A level First Year of Sixth form. Main topics are: Atomic Structure, Mass Spectrometry, Orbitals, Radioactivity, Gas laws, Isomers, Bonding (very detailed), Shapes of molecules, Redox, Thermodynamics, and Equilibria.