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.
