Bohr's Theory and orbitals Flashcards
continuous spectrum
white light passed through a prism broken up into a continuous spread of colours
line emission spectrum
light from a hydrogen discharge tube is passed through a prism and coloured lines on a black backround are observed.
why do different elements produce line emission spectra?
they have different electronic configurations which give rise to different electron transitions.
limitations to bohr’s theory
only worked for hydrogen atoms
did not take wave particle duality of electrons into account
did not allow for heisenberg’s uncertainty principle
did not explain the discovery of sublevels
energy levels
fixed energy values an electron can have in an atom. energy levels are given the letter n
ground state
state where an electron occupies lowest available energy level
excited state
state where electrons occupy a higher energy level than those available in the ground state
what happens when you give an atom energy (heat or electricity)
the atom in the ground state absorbs a fixed amount of energy causing it to jump to a higher energy level. this atom is now in the excited state. this causes the atom to be unstable so the electron falls back to a lower energy level
what happens when the electron falls back to a lower energy level
a photon of light of a fixed energy value is emitted. the energy of the photon corresponds to the energy difference between the excited state and the lower energy level.
the definite amount of energy emitted appears as a line of a particular colour in the line emission spectrum.
use bohr’s atomic theory to explain the line emission spectra of hydrogen
when an atom is in the ground state electrons are restricted to energy levels that have fixed energy values and occupy the lowest available energy level.
the atom absorbs a fixed amount of energy and the e can jump to a higher energy level ie the excited state
the atom in the excited state is unstable and the e falls back down to energy level with the emission of a photon of light
the energy difference between the energy levels determines the definite frequency of the photon that appear as lines of a fixed colour on an emission spectrum
why does hydrogen have so many electron transitions if it has only one electron
in a sample of hydrogen there are millions of hydrogen atoms. they don’t all absorb the same amount of energy so the electron jumps to a different higher state. when they fall back different photons of light are emitted due to the different energy levels.
what does AAS stand for
Atomic Absorption spectroscopy
what does an AAS measure?
the amount of light absorbed by a sample. these are dark lines on a coloured background.
benefits of AAS
it is qualitative- used to detect heavy metals in water. the wavelength of light absorbed is characteristic of the element.
it is quantative: used to figure out the concentration of a sample- more light absorbed=higher the concentration.
what is the principal behind AAS
atoms of the element in the ground state absorb light of a particular wavelength that is characteristic of that element
the amount of light absorbed is directly proportional to the concentration of the element in the sample. the more light absorbed=the greater no of atoms of that element.
what instrument is used to measure an AAS
atomic absorbtion spectrocopy/spectrometry
compare line emission spectra to atomic absorbtion spectra
line emission spectra:
coloured lines on a black background
does not tell you the concentration of a sample ie not quantitative
atomic absorbtion spectra
dark lines on a coloured background
quantitative: amount of light absorbed is directly proportional to its concentration
what is the aim of flame tests
to carry out flame test analysis of different metal salts
method of flame tests
- clean a nichrome wire by dipping it into HCl and holding it into the blue flame of the bunsen burner to ensure no colour is observed on the flame.
- dip the nichrome wire into a salt sample and hold it into the blue flame.
- note the colour of the flame produced
- repeat steps 1-3 using different salts.
lithium
crimson
potassium
lilac
barium
green
strontium
red
copper
blue-green
sodium
yellow
sublevel
a subdivision of a main energy level that consists of 1 or more orbitals of the same energy
evidence for sublevels
- first ionisation energies increase across a period
- only fixed frequencies of energy are emitted from atoms
heisenberg’s uncertainty priciple
it is not possible to measure, at the same time both the velocity and position of an electron
what is the wave particle duality of electrons?
Electrons behave like a particle and a wave.
if you want to measure the velocity of an electron it is impossible as you cannot know the exact position of an electron and visa versa.
HUP and wave particle duality make it difficult to establish a covalent radius.
why do HUP and wave particle duality make it difficult to establish a covalent radius?
electrons do not travel in fixed paths, so we can only know the probability of finding an electron in a particular position in an atom.
limitations of bohr theory
- only worked for hydrogen,
2.did not allow for heisenbergs uncertainty principle - did not explain discovery of sublevels
modifications to bohr theory
electrons occupy orbitals not orbits.
electrons have wave nature so we can only know the probability of finding electrons
energy levels are split into sublevels
atomic orbitals
a region of space where there is a high probability of finding electrons. orbitals can hold a max of 2 electrons
what are the 4 different orbital shapes?
s, p, d, f
what shape are s orbitals
spherical
what shape are p orbitals
dumbbell
how many orbitals does the s sublevel have
1
how many orbitals does a p sublevel have
3
orbitals in d sublevel
5
what are the sublevels in order of energy level?
1s, 2s, 2p, 3s, 3p, 4s, 3d, 4p, 4d, 4f
orbitals in f sublevel
7
how many electrons in each orbital
2
aufbau principle
electrons occupy the lowest available energy levels first.
hund’s rule of max multiplicity
electrons occupy orbitals singly before occupying them in pairs.
pauli’s exclusion principle
no more than 2 electrons can occupy an orbital + they must have an opposite spin.
what are the exceptions when writing electronic configuration?
copper and chromium
highest energy level=
the highest number in front of letters when writing electronic configuration.
amount of sublevels =
amount of letters
spectroscopy
the study of the absorption and emission of light by matter
spectrum
image or info generated after matter has absorbed or emitted light
absorption spectrum
dark lines on a coloured background
atomic number
the total number of protons in the nucleus of an atom
mass no
the no of protons and neutrons in the nucleus of an atom
what are the 3 series of lines in the line emission spectra called
lyman
balmer
paschen
Lyman series
UV region
excited state to n=1
which series of lines are invisible
paschen
lyman
paschen
IR region
excited state to n=3
which series of line is visible
Balmer
Balmer
visible region (coloured lines in line emission spectra)
excited state to n=2
what electron transition emits a red photon
n=3 to n=2
what electron transition emits a cyan photon
n=4 to n=2
what electron transition emits a blue photon
n=5 to n=2
what electron transition emits a purple photon
n=6 to n=2
give evidence for the existence of energy levels in atoms
flame tests
ionisation energies of elements
why does H have so many electron transitions if it only has one e?
in a sample of H there are millions of H atoms. not every atom absorbs the same amount of energy, so the electrons jump to different higher excited states
when these e fall from the higher energy level back to a lower energy level, photons of different energies are released which results in different lines in the emission spectrum
give a similarity of line emission and atomic absorption spectra
both qualitative
why is it difficult to specify the absolute boundary of an atom
due to Heisenberg’s uncertainty principle
uses of AAS
used to detect heavy metals in water
drug tests
blood alcohol conc tests
which scientist figured out the probability of finding an e in a particular sublevel
Schrödinger
compare s and p sublevel
S:
contains 1 spherical shaped orbital
holds max 2 e
lower in energy
P:
contains 3 dumbbell shaped orbitals
holds max 6 e
higher in energy
describe the difference between an atomic orbit as described by bohr and an atomic orbital
orbit
2D
HUP not taken into account
electron definitely located there
orbital
3D
HUP taken into account
high probability of finding an e there
using diagrams compare a p orbital and a p sublevel
orbital:
holds max 2 e
(show diagram of arrows on line)
is 1 orbital
(show diagram of single dumbbell orbital)
sublevel
holds 6 e
(show same diagram but ensure to label orbitals ie xyz)
contains 3 orbitals
(show 3 orbitals on axis)
explain why there is no orange or yellow line in the H emission spectrum
there is no transition that corresponds to those photons as e cannot exist between sublevels
what is the e configuration of chromium
4s1 3d5
why do we move one e from 4s to 3d in chromium
sublevels that are exactly half filled or full have extra stability
the 4s and 3d sublevels are both exactly half filled which is more stable than if the 4s were full and there were 4 e in the 3d sublevel
this only happens because the 4s and 3d sublevel are so close in energy
why do we move one e from 4s to 3d in copper
sublevels that are exactly half filled or full have extra stability
the 4s sublevel is exactly half filled and 3d sublevel is full which is more stable than if the 4s were full and there were 9 e in the 3d sublevel.
this only happens because the 4s and 3d sublevel are so close in energy
write the e configuration of copper
4s1 3d10
