CHEM1101 Lecture Notes - Lecture 5: Atomic Absorption Spectroscopy, Principal Quantum Number, Atomic Spectroscopy
Relate absorption and emission of photons to
changes in electron energy levels
Spectroscopy - study of the interaction of matter with electromagnetic
radiation
e.g. MRI - uses radio waves
Each atom has different energy atomic orbitals, so distance between
atomic orbitals also different
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Attractive electrostatic forces hold an electron within an atom
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The lower the atom's energy state, the more energy needed to
remove its electron
○
Energy must be supplied to remove electron from atom
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When atom absorbs photon of sufficiently high energy, electron is
ejected (ie. Atom ionises)
○
Since excited states unstable, atoms give up excess energy
to return to ground state, by emitting photons (or colliding
with other atoms)
▪
FOCUS: atom gains energy but does not ionise, instead moving
from lowest energy/ground state to a higher energy/excited state
○
Absorption of photons by free atoms has 2 results
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Screen clipping taken: 11/06/2017 11:19 AM
Gaps between energy levels are fixed and energy of the electron in the
atom is quantised
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Higher absorbance = less light gets through
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Absorbance = how much light can pass through a solution
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When an e- drops from a higher to lower level, it sheds excess energy, a
positive amount, by emitting a photon
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L13
5.1
Sunday, 11 June 2017
11:13 AM
5. Spectroscopy Page 1
positive amount, by emitting a photon
Can absorb a photo and change from its most stable, lowest energy
state (ground state), to a less stable, higher energy state (excited state)
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When absorbs a photon, its electron can undergo a transition to an
orbital that has a larger principle quantum number ie. Higher energy
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Diagram shows 1s->2p transition in hydrogen atom
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When hydrogen atom in ground state, absorbs light, then converted to
excited state, whereby electron occupies 2p orbital
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Hydrogen atom
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Document Summary
Relate absorption and emission of photons to changes in electron energy levels. Spectroscopy - study of the interaction of matter with electromagnetic radiation e. g. mri - uses radio waves. Each atom has different energy atomic orbitals, so distance between atomic orbitals also different. Attractive electrostatic forces hold an electron within an atom. Energy must be supplied to remove electron from atom. The lower the atom"s energy state, the more energy needed to remove its electron. Absorption of photons by free atoms has 2 results. When atom absorbs photon of sufficiently high energy, electron is ejected (ie. atom ionises) Focus: atom gains energy but does not ionise, instead moving from lowest energy/ground state to a higher energy/excited state. Since excited states unstable, atoms give up excess energy to return to ground state, by emitting photons (or colliding with other atoms) Gaps between energy levels are fixed and energy of the electron in the atom is quantised.