inorganic chem Flashcards
a) how can electromagnetic radiation be described + characterised?
- described in terms of waves
- characterised in terms of wavelength and/ or frequency
visible light travels in…
waves
what are waves measured in?
what is the symbol?
m
λ
what is frequency?
the no. of waves which go by a fixed point in 1 second
what is frequency measured in?
what is the symbol?
f
Hz or s-1
what is the speed of light formula, showing the relationship between frequency and wavelength?
c=f x λ
what is the electromagnetic spectrum?
the different types of radiation arranged in order of wavelength
wavelength of what particular type of light is measured in nm rather than m?
visible light
describe electromagnetic radiation
-can be described as a wave (have a wavelength and frequency)
-can also be described as a particle
hence has DUAL NATURE
what is the mnemonic for the electromagnetic spectrum
Good Gamma rays Xylophones X-rays Use Ultraviolet Very Visible Interesting Infrared Musical Microwaves Rhythms Radiowaves
what is the e/m radiation wavelength range?
from 10-¹²m to 10²m
as λ increases, f …
as f increases, λ …
as λ increases, f decreases
as f increases, λ decreases
what is visible light’s range?
400-700nm
what is 1 nm equal to in m?
1nm = 10-⁹m
when electromagnetic radiation is absorbed or emitted by matter, it behaves like…?
a stream of particles a.k.a- photons
what is a photon
carries quantised energy proportional to the frequency of radiation
what happens when a photon is absorbed or emitted?
- energy is gained or lost by electrons within the substance
- the photons in high frequency radiation can transfer greater amounts of energy than photons in low frequency radiation
the energy associated with a single photon is given by the formula…
E = hf or E = hc / λ
the energy associated with a one mole of photons is given by the formula…
E = Lhf or E = Lhc / λ
what units are generally used for energy?
kJmol-¹
what happens when energy is transferred to atoms?
electrons within the atoms may be promoted to higher energy levels
give direct evidence for the existence of energy levels
the light energy emitted by an atom produces a spectrum made up of a series of lines at discrete (quantised) energy levels
absorption + emission spectra can be used to identify + quantify an element. why?
each element in a sample produces characteristic spectra.
a.k.a- each element has its own spectrum
describe absorption spectroscopy
-electromagnetic radiation is directed at an atomised sample. radiation is absorbed as electrons are
promoted to higher electrons
-an absorption spectrum is produced by measuring how the intensity of absorbed light varies with wavelength
describe emission spectroscopy
- high temperatures are used to excite the electrons with atoms. as the electrons drop to lower energy levels, photons are emitted
- an emission spectrum of a sample is produced by measuring the intensity of light emitted at different wavelengths
describe atomic spectroscopy
the concentration of an element within a sample is related to the intensity of light emitted or absorbed
what are the five steps to colorimetry?
- prepare 4 or 5 standard solutions of the chemical whose concentration you are trying to determine
- choose a filter complementary to the colour of the sample
- use a blank (solvent) first e.g- deionised water
- produce a callibration graph by inserting the standards into the device and measuring absorbance
- now place unknowns in the device and measure absorbance. use the graph to determine concentration
what is the principal quantum number? what is it’s abreviation name?
it (n) refers to the energy level e.g- n=1 is the energy level closest to the nucleus
within each energy level is a what?
subshell(s)
within each subshell is a what?
Atomic Orbital (A.O)
what is an atomic orbital?
a region in space where there is a greater than 90% chance of finding an electron. every A.O holds 2 electrons maximum
describe the energy level n=1
this contains a subshell called an “s” subshell. this “s” subshell contains 1 A.O. we also call this an sA.O which is spherical
describe the energy level n=2
this contains 2 subshells- a larger s subshell and a p subshell
the s subshell contains 1 A.O (spherical)
a p subshell contains 3 p A.Os, each pA.O is dumbbell shaped
each of these pA.Os contains a maximum of 2 electronsso a p subshell contains 6 electrons
∴ the 2nd energy level, n=2 contains 8 electrons (2 in s and 6 in p)
describe the s subshell
contains only 1 atomic orbital
all sAOs are spherical- they simply vary in size
describe the p subshell
contains 3 p atomic orbitals
each p is dumbbell shaped
each of these p AOs contains a maximum of 2 electrons
so a p subshell contains 6 electrons
describe the energy level n=3
there are 3 subshells:
- an s subshell with 1 sAO (2 e-)
- a p subshell with 3 pAOs (6e-)
- a d subshell with 5 dAOs (10e-)
total e-s = 18e-
each dAO holds 2e-s max. so each subshell holds 10e-s
describe energy level n=4
there are 4 subshells:
- an s subshell with 1 sAO (2 e-)
- a p subshell with 3 pAOs (6e-)
- a d subshell with 5 dAOs (10e-)
- an f subshell with 7 fAOs (14 e-)
what does the Aufbau Principle
tells us that the electrons must fill the lowest energy AOs first
4s must be filled before 3d
what do we can AOs which are of equal energy?
degenerate
what are two ways of representing the Aufbau Principle
- an energy diagram (each line represents an AO)
- box notation (a box represents an AO and an arrow represents an e-)
what does Hund’s rule state?
that electrons must be filled up ___, with arrows facing the same way, before pairing in subshells which contains degenerate orbitals
what does the Pauli exclusion principle state?
that no 2 electrons can have the same 4 quantum numbers (which is why electrons in an AO have opposite spins)
what does “n” denote?
“n” displays the main energy level
what does “l” denote?
“l” displays the angular momentum quantum number. this denotes the type of subshell
what does “m₁” a.k.a- m l denote?
“M l” is the magnetic quantum number. this gives the orientation of the AO within the subshell (basically show how many AOs there are)
what does the “m₅” a.ka- m s denote?
“M s” is the spin magnetic quantum number. this relates to the spin of the electron and has values +½ or -½
what are the possible l values?
s- 0
p- 1
d- 2
what are the possible M l values?
s- 0
p- -1, 0, 1
d- -2, -1, 0, 1, 2
what are the possible M s values?
+½ or -½
why is the three atom molecule H₂O angular, yet the three atom CO₂ is linear? what dictates shape?
electron repulsions. bonds contain two electrons- they want to move as far apart as possible
what is the shape of a molecule determined by?
electron-electron repulsions between bonding and non-bonding pairs. non-bonding pairs exert a greater repulsion than bonding pairs
which exerts a greater electron repulsion- bonding or non-bonding pairs?
non-bonding pairs exert a greater repulsion than bonding pairs
l.p-l.p > l.p-b.p > b.p-b.p
what do we use to determine the shape of a molecule?
VSEPR
Valence Shell Electron Pair Repulsion Theory
what are the 7 steps of
VSEPR?
- identify central atom, how many outer electrons are there?
- add 1e- for each atom it’s bonded to
- add 1e- for each -ve charge
- remove 1e- for each +ve charge
- add together then divide by 2- this gives the number of electron pairs
- look at the formula and decide how many b.p or l.p are present
- determine shape
bond angle for linear?
no. of bond pairs?
180
2
bond angle for trigonal planar?
no. of bond pairs?
120
3
bond angle for tetrahedral?
no. of bond pairs?
109.5
4
bond angle for trigonal bipyramidal?
no. of bond pairs?
180, 90 and 120
5
bond angle for octahedral?
no. of bond pairs?
180, 90
6
bond angle for trigonal pyramidal?
no. of bond pairs?
107
3
bond angle for square planar?
no. of bond pairs?
90
4
what are transition metals defined as?
metals which have an incomplete d subshell in one of their ions
when a transition metal loses an electron, it loses it from which subshell first?
the 4s subshell
why do transition metals act as catalysts?
they have space in their d subshells to form “complexes” which have a lower Ea
describe catalysts
can be classed as Homogeneous (same physical state as reactants) or Heterogeneous (different state)
homogeneous catalysts have variable “oxidation states”
what can an oxidation state/ number be used for?
we can determine if a substance has been oxidised or reduced using it
what oxidation state do ELEMENTS have?
0
what oxidation state do IONS have?
have an OS equal to their charge
what oxidation state do MOLECULES have?
have an OVERAL OS of zero, with the OSs of the atoms in the molecule adding to zero.
give each atom an OS equal to the charge it WOULD have as an ION
what oxidation state do GROUP IONS have?
the OS of the individual atoms is equal to the OVERALL charge on the ion
is an increase in OS oxidation or reduction?
increase = oxidation
is a decrease in OS oxidation or reduction?
decrease = reduction
