inorganic chemistry Flashcards
how can EM radiation be described?
as both a wave and a particle- dual nature
when does EM radiation behave as particles?
when it is absorbed or emitted, particles are called photons
what do photons carry?
quantised energy, proportional to the frequency of radiation
what happens when a photon is absorbed or emitted?
energy is gained or lost by the electrons of the material
what happens when energy is transferred to atoms?
electrons within it may be promoted to higher energy level
what happens when an electron moves from a higher to lower energy level?
a photon is emitted, the light energy emitted produces a spectrum that is made up of a series of lines at discrete energy levels
wavelength definition
distance between two crests
frequency definition
number of waves per second
relationship between frequency and wavelength
as one increases, the other decreases - inversely proportional
relationship between energy and frequency
frequency increases = energy increases
what happens as the concentration of the compound in absorption spectroscopy increases?
intensity of radiation absorbed increases, intensity of radiation transmitted decreases
what is an orbital?
an area of space where there is a 90% chance of finding an electron
what tell us where in an orbital to find an electron?
quantum numbers
what is a principal quantum number (n)?
represent electron shells
i.e n=1, first shell
n=2, second shell
what are the four subshells?
s, p, d, f
how many electrons can each orbital hold?
2
angular momentum quantum number
s subshell = 0
p subshell = 1
d subshell = 2
f subshell = 3
what does degenerate mean?
of equal energy
magnetic quantum numbers
no. of orbitals = no. of possible magnetic quantum numbers e.g. 2p subshell could have -1,0 or +1
- you can choose any of the possible magnetic quantum numbers
spin quantum numbers
- can either be +1/2 or -1/2
- the two electrons in an orbital will spin opposite ways
pauli exclusion principle
no two electrons can have the same 4 quantum numbers
aufbau principle
- orbitals of lowest energy fill up first
- lowest energy orbitals are not necessarily closest to the nucleus (4s fills up before 3d)
hunds rule of maximum multiplicity
- each electron will take a separate orbital until all the orbitals in the subshell are half-filled
what is ionisation energy?
energy required to remove one mole of electrons from one mole of gaseous atoms
why does the first I.E of Beryllium not follow the trend?
removing an electron involves breaking a full subshell, which requires more energy
what do full and half full shells provide for atoms?
more stability
what is the best definition for a transition metal?
it can form at least one ion with an incomplete d subshell
which elements dont match the definition for a transition metal?
scandium and zinc
which two elements do not follow the aufbau principle and why?
copper and chromium, due to the special stability associated with subshells being full or half full
which subshell are atoms lost from first when ions are formed?
4s
oxidation number in a free or uncombined element
zero
oxidation number in single atom ions
same as number charge on the ion
oxidation number of hydrogen in compounds
usually +1
in hydrides it’s -1
oxidation number of oxygen in compounds
usually -2
in peroxides it’s -1
what must the sum of all the oxidation numbers in a molecule equal?
zero
what must the sum of all the oxidation numbers in a polyatomic ion equal?
the overall charge on the ion
what does an increase in oxidation number mean?
oxidation has occurred
what does a decrease in oxidation number mean?
reduction has occured
do compounds containing metals with a high oxidation number act as oxidising or reducing agents?
oxidising - they are reduced to a lower oxidation number
do compounds containing metals with a low oxidation number act as oxidising or reducing agents?
reducing - they are oxidised to a higher oxidation number
what is changing oxidation states often characterised by?
a change in colour
what does a transition metal complex consist of?
a central metal ion surrounded by ligands
what is a ligand?
a molecule or ion electron donor which bonds to the metal ion by the donation of one or more electron pairs to unfilled metal ion orbitals
what are monodentate?
ligands which donate 1 electron pair
what are bidentate?
ligands which donate 2 pairs of electrons - pairs must be from separate parts of the molcule, not the same atom
what is a coordination number?
the number of bonds between the ligand and the central ion
when naming complexes, when should -ate be added to the metal?
if overall charge on ion is negative
dative covalent bonds
when one atom provides both electrons that form the covalent bond
how are transition metal complexes able to absorb light?
due to the 5 degenerate d orbitals splitting in terms of energy
why do the orbitals along the axis have a higher energy than the other in metal complexes?
because the ligands approach the metal along the axes and the electrons that lie on these axes will be repelled y those in the ligand molecules, resulting in more energy - called splitting of d orbitals
relationship between ligand size and energy difference
larger ligand = larger energy difference
what happens when compounds absorb light from the visible spectrum?
the colour corresponding to the wavelength is removed and the colour that remains is the complementary colour (opposite in the colour wheel)
when are electron transitions more likely to occur in the UV part of the spectrum?
when the ligands are strong field (cause greatest splitting/highest energy difference)
what colour will the compound be if the transitions occur in the UV part of the spectrum?
colourless
why are zinc and scandium complexes colourless?
zinc (2+) has a full 3d subshell
scandium (3+) has an empty 3d subshell
2 categories of transition metal catalysts
homogeneous and heterogeneous
homogeneous catalyst (definition)
catalyst that is in the same state as the reactants
heterogeneous catalyst (definition)
catalyst that is in a different state to the reactants
homogeneous catalyst (explanation)
changing oxidation states with the formation of intermediate complexes
heterogeneous catalyst (explanation)
formation of activated complexes and the adsorption of reactive molecules onto active sites.
the presence of unpaired electrons is thought to allow activated complexes to form, this can provide alternative reaction pathways with a lower activation energy.
what is adsorption?
the “sticking” of a molecule onto the surface of a catalyst
what happens to oxidation number when transition metals are used as catalysts?
oxidation number may change, but the original state will be regenerated at the end of the reaction
why is the shape of a molecule important?
it will determine its properties and uses
how do you calculate the number of electron pairs?
add the number of outer electrons on central atom to the number of atoms attached to the number of atoms attached to the central atom, then divide by 2
what shape is a molecule with 2 bonded pairs?
linear
what shape is a molecule with 3 bonded pairs?
trigonal planar
what shape is a molecule with 4 bonded pairs?
tetrahedral
what shape is a molecule with 5 bonded pairs?
trigonal bipyramidal
what shape is a molecule with 6 bonded pairs?
octahedral
what are the shapes of molecules or polyatomic ions determined by?
the shapes adopted by the atoms present, based on the arrangement of electron pairs
