Unit 1 Flashcards
Emission Spectrum
Energy is transferred to atoms.
The electrons within the atoms have been excited and promoted to a higher energy level.
The electrons fall back down to a lower energy level.
The energy is released as a photon of light is emitted.
Absorption spectrum
Electromagnetic radiation is directed at an atomised sample.
Radiation is ABSORBED as electrons are promoted to higher energy levels.
An absorption spectra is produced by measuring how the intensity of absorbed light varies with wavelength.
Note : the wavelength of the absorbed light is specific to a particular element.
S sub shell
Spherical shaped atomic orbital
Holds 2 electrons max
P subshell
3 dumbbell shaped p atomic orbitals, each holding 2 electrons max.
The p subshell can hold a maximum of 6 electrons.
D subshell
Has 5 d atomic orbitals each holding a max of 2 electrons.
The d subshell can hold a max of 10 electrons.
Ionisation energy
The energy required to remove one mole of electrons from one mole of atoms in the gaseous state.
Aufbau Principle
Electrons fill each degenerate orbital in order of increasing energy.
Hunds Rule
Electrons fill each degenerate orbital singly and with parallel spins before pairing occurs.
Pauli Exclusion Principle
No 2 electrons can have the same 4 quantum numbers.
4 quantum numbers
n : principle QN ; denotes the main energy level
l : angular momentum QN ; denotes the sub-shell the electron is in (s=0, p=1, d=2)
ml : magnetic QN; denotes the atomic orbital the electron is in (s=0, p=0,+1,-1, d=0, +1,+2,-1,-2)
ms : magnetic spin QN ; denotes the spin on the electron
Atomic Orbital
A region is space in which there is a >90% chance of finding an electron
2 bond pairs
Linear (180)
3 bond pairs
Trigonal planar (120)
4 bond pairs
Tetrahedral (109.5)
5 bond pairs
Trigonal bipyramidal (120 and 90)
6 bond pairs
Octahedral (90)
3 bond pairs + 1 lone pair
Pyramidal
2 bond pairs + 2 lone pairs
Angular
3 bond pairs + 2 lone pairs
Trigonal planar
4 bond pairs + 2 lone pairs
Square Planar
2 bond pairs + 3 lone pairs
Linear
Transition metals
The d block transition metals are metals with an incomplete d sub-shell in at least one of its ions.
What 2 metals do not follow Aufbau’s principle ?
Copper
Chromium
There is a special stability associated with a half filled or completely full orbital.
Oxidation
An increase in oxidation state.
Reduction
A decrease in oxidation state.
Ligand
Ligands are negative ions or uncharged molecules with one or more non bonding pairs of electrons.
Electron donors, bond to TM ions via a dative bond
Dative bond
A covalent bond in which both electrons in the bond come from the same atom.
Complex
A central metal ion surrounded by ligands.
Degenerate
The orbitals have the same / equal energy.
Co-ordination number
The number of bonds from the ligand to the central metal ion
Neutral mono-dentate ligands
H2O
NH3
CO
Charged mono-dentate ligands
F-
Cl-
Br-
I-
CN-
OH-
Neutral bi-dentate ligands
C2H8N2
Charged bi-dentate ligands
C2O4 2-
Oxalate ion
Charged poly-dentate ligand
EDTA 4+
Transition metal colours
An isolated TM ion has 5 degenerate d atomic orbitals.
As the ligand approaches the TM along the axes, the electrons in the d orbital which lies on the axes are repelled by the electrons of the approaching ligands.
This results in splitting of the 5 d atomic orbitals.
When light of a particular wavelength is absorbed, electrons can be promoted to the higher energy d orbitals.
If the absorbed energy is in the VISIBLE part of the E/M spectrum (400-700nm), the colour of the TM compound will be complementary to the absorbed colour.
Strong field ligands
Give a larger energy gap. Complexes containing strong field ligands are more likely to absorb ultra violet light, so the complex will be colourless. (200-400nm)
Weak field ligands
Give a small energy gap. Complexes containing weak field ligands are more likely to absorb visible light, making them coloured. (400-700nm)
Spectrochemical Series
CN- > NH3 > H2O > OH- > F- > Cl- > Br- > I-
What are uses of Transition metals ?
Transition metals and their compounds are used as catalysts, due to the variability in oxidation states.
Heterogeneous catalysts
A catalyst in a different physical state to the reactants.
Homogeneous catalysts
A catalyst in the same physical state to the reactants.
How do catalysts work ?
The reactants are ADsorbed onto the surface of the catalyst.
They form weak bonds with the transition metal due to the incomplete d sub-shell.
This lowers the activation energy.
The molecules leave the surface as products.
Dynamic equilibrium
The rate of the forward reaction is equal to the rate of the reverse reaction.
The concentration of reactants and products is constant.
Ways in which the position of equilibrium can be moved
Temperature : increase - shifts to endo. decrease - shifts to exo
Concentration : increase - shifts to opposite side. decrease - remains on same side
Pressure : increase - shifts to side with less moles of gas. decrease - more moles of gas
Equilibrium constant
K - characterises the equilibrium composition of the reaction mixture.
K > 1
Equilibrium lies on the right
K < 1
Equilibrium lies on the left
K = 0
Equilibrium neither lies left nor right
What is the value of K dependent on ?
Temperature
Endothermic reactions : increase in temperature : increase in K
Exothermic reactions : increase in temperature : decrease in K
Acid
Proton (H+) donor
Alkali
Proton (H+) acceptor
Amphoteric
Used to describe a substance that acts as both an acid and a base.
Kw
Equilibrium constant
At 24C has value 1.0 x 10^-14
Strong acid/base
Substances which fully dissociate in aqueous solution
Weak acids/bases
Substances that partially dissociate in aqueous solution.
Strong acids
Hydrochloric acid
Sulphuric acid
Nitric acid
Weak acids
Carboxylic acids
Strong bases
Sodium hydroxide
Potassium hydroxide
Calcium hydroxide
Weak bases
Amines
(Ammonia)
Conjugate acid
Formed by the gain of a proton
Conjugate base
Formed by the loss of a proton
Properties of strong acids
Have a lower pH than weak acids
Conduct better than weak acids
React with metals faster than weak acids
Properties of strong bases
Have a higher pH than weak bases
Conduct better than weak bases
Strong acid + base
Neutral solution
Weak acid + base
Neutral solution
Strong acid + weak base
Acidic solution
Weak acid + strong base
Basic solution
To explain changes in the pH of solutions
Because this is ACIDIC / BASIC there must be an XS of H+/OH- ions.
The OH-/H+ ions must be reacting with the large concentration of +/- ions, leaving an XS of H+/OH- ions.
Buffer
A buffer solution is one in which the pH remains approximately constant when small amounts of H3O+, OH- ions or water are added.
Acidic buffer : weak acid + its salt
Basic buffer : weak base + its salt
To explain how a buffer works
If an acid/base was added to this buffer mix, we’d expect the pH to decrease/increase, but instead it remains approximately constant.
This is because the H3O+ / OH- ions react with the -ve/ +ve salt ions.
Indicator
Indicators are weak acids which in aqueous solutions, the colour of the acid is distinctly different from that of its conjugate base.
Standard Enthalpy of formation
The enthalpy change when one mole of a substance is formed from its elements at STP.
( 25C/ 298K : 1 mole : 1 atmosphere pressure)
Entropy
A measure of the degree of disorder in a system. Entropy increases as temperature increases.
Solids have a low entropy
Gases have a high entropy
2nd Law of Thermodynamics
The total entropy of a system and its surroundings increases for a spontaneous event.
3rd Law of Thermodynamics
The entropy of a perfect crystal is zero at 0K
Feasible
A feasible reaction is one that tends towards the products side rather than the reactants.
When is delta G negative ?
Delta H is negative and Delta S is positive
When is delta G positive ?
Delta H is positive and Delta S is negative
Rate equation
Tells us how many molecules are involved in the slowest/ rate determining step.
