the bohr model for the electrons electronic structure – how the electrons are arranged inside the...
TRANSCRIPT
The Bohr model for the electronsThe Bohr model for the electrons
Electronic structure – how the electrons Electronic structure – how the electrons are arranged inside the atomare arranged inside the atomApplying the quantum principle of energyApplying the quantum principle of energyTwo parameters:Two parameters:– EnergyEnergy– PositionPosition
Learning objectivesLearning objectives
Describe the basic principles of the Bohr modelDescribe the basic principles of the Bohr modelDistinguish between the “classical” view and the Distinguish between the “classical” view and the “quantum” view of matter“quantum” view of matterDefine atomic orbitalsDefine atomic orbitalsDistinguish between the Bohr orbit and atomic Distinguish between the Bohr orbit and atomic orbitalorbitalApply quantum numbers and atomic orbitals to Apply quantum numbers and atomic orbitals to building atoms and the periodic tablebuilding atoms and the periodic tableDescribe periodic trends in terms of electronic Describe periodic trends in terms of electronic structurestructure
Bohr’s theory of the atom: applying Bohr’s theory of the atom: applying photons to electronic structurephotons to electronic structure
Electrons occupy specific Electrons occupy specific levels (orbits) and no levels (orbits) and no othersothersOrbits have Orbits have energyenergy and and sizesizeElectron excited to higher Electron excited to higher level by absorbing photon level by absorbing photon Electron relaxes to lower Electron relaxes to lower level by emitting photonlevel by emitting photonPhoton energy exactly Photon energy exactly equals gap between levelsequals gap between levelsLarger orbits are at higher Larger orbits are at higher energyenergy
Size of energy gap determines Size of energy gap determines photon energyphoton energy
Small energy gap, low Small energy gap, low frequency, long frequency, long wavelength (red shift)wavelength (red shift)
High energy gap, high High energy gap, high frequency, short frequency, short wavelength (blue shift)wavelength (blue shift)
The full spectrum of lines for HThe full spectrum of lines for H
Each set of lines in the H spectrum comes from Each set of lines in the H spectrum comes from transitions from all the higher levels to a particular level.transitions from all the higher levels to a particular level.The lines in the visible are transitions to the second levelThe lines in the visible are transitions to the second level
The Bohr orbitsThe Bohr orbits
Bohr orbits have quantum numbers Bohr orbits have quantum numbers nn– n = 1 (capacity 2)n = 1 (capacity 2)– n = 2 (capacity 8)n = 2 (capacity 8)– n = 3 (capacity 8)n = 3 (capacity 8)
Bohr orbits and the periodic tableBohr orbits and the periodic table
Elements in the same group have the Elements in the same group have the same number of electrons in outer Bohr same number of electrons in outer Bohr orbitorbit
Successes and shortcomings of BohrSuccesses and shortcomings of Bohr
Couldn’t explain why orbits were allowedCouldn’t explain why orbits were allowedOnly successful agreement with experiment was Only successful agreement with experiment was with the H atomwith the H atom
Introduced connection between spectra and Introduced connection between spectra and electron structureelectron structureConcept of allowed orbits is developed further Concept of allowed orbits is developed further with new knowledgewith new knowledgeNonetheless, an important contribution, worthy Nonetheless, an important contribution, worthy of the Nobel prizeof the Nobel prize
Electrons are waves too!Electrons are waves too!
Life at the electron level is very differentLife at the electron level is very differentKey to unlocking the low door to the secret garden of Key to unlocking the low door to the secret garden of the atom lay in accepting the wave properties of the atom lay in accepting the wave properties of electronselectronsDe Broglie wave-particle duality De Broglie wave-particle duality All particles have a wavelength – wavelike nature. All particles have a wavelength – wavelike nature. – Significant only for very small particles – like electrons or Significant only for very small particles – like electrons or
photons photons – As mass increases, wavelength decreasesAs mass increases, wavelength decreases
Electrons have wavelengths about the size of an atom Electrons have wavelengths about the size of an atom – Electrons are used for studying matter – electron microscopyElectrons are used for studying matter – electron microscopy
Electron microscopes can peer within – Electron microscopes can peer within – waves interacting with matterwaves interacting with matter
Heisenberg Uncertainty Principle: Heisenberg Uncertainty Principle: the illusive electronthe illusive electron
We can predict the motion of a ball;We can predict the motion of a ball;But not an electron: problems locating small But not an electron: problems locating small objectsobjects
The Quantum Mechanics: waves of The Quantum Mechanics: waves of uncertaintyuncertainty
System developed that incorporated these System developed that incorporated these concepts and produced an concepts and produced an orbitalorbital picture picture of the electronsof the electronsNo longer think of electrons as particles No longer think of electrons as particles with precise location, but as waves which with precise location, but as waves which have probability of being in some region of have probability of being in some region of the atom – the orbitalthe atom – the orbitalImpossible with the Impossible with the classicalclassical mechanics of mechanics of NewtonNewton
Orbitals are described by quantum Orbitals are described by quantum numbersnumbers
Each orbital has unique setEach orbital has unique set
1s, 2p, 3d etc.1s, 2p, 3d etc.
Number describes energyNumber describes energy
Letter describes shapeLetter describes shape– S zero dimensions S zero dimensions – P one dimensionP one dimension– D two dimensionsD two dimensions– F three dimensionsF three dimensions
Getting from the orbitals to the Getting from the orbitals to the elementselements
All elements have the same setAll elements have the same set
Atomic number dictates how many are Atomic number dictates how many are filled – how many electrons are addedfilled – how many electrons are added
Filling orbitals follows a fixed pattern: Filling orbitals follows a fixed pattern: lowest energy ones firstlowest energy ones first
Orbital energy levels in H and other Orbital energy levels in H and other elementselements
How many per orbital?How many per orbital?
Electrons share orbitals (only two allowed)Electrons share orbitals (only two allowed)
A consequence of “spin”A consequence of “spin”
How many electrons can be added How many electrons can be added to the orbitalsto the orbitals
1s, 2s, 3s etc. 1s, 2s, 3s etc. 2 electrons 2 electrons
2p, 3p, 4p etc.2p, 3p, 4p etc. 6 electrons 6 electrons
3d, 4d etc. 3d, 4d etc. 10 electrons10 electrons
4f, 5f etc. 4f, 5f etc. 14 electrons14 electrons
Add electrons to the orbitals – Add electrons to the orbitals – lowest firstlowest first
2p
3d
3p
4p4s
3s
2s
1s
H(z = 1)
2p
3d
3p
4p4s
3s
2s
1s
He(z = 2)
Fill lowest orbitalFill lowest orbital
2p
3d
3p
4p4s
3s
2s
1s
Li(z = 3)
Begin next orbitalBegin next orbital
2p
3d
3p
4p4s
3s
2s
1s
Be(z = 4)
Fill 2sFill 2s
2p
3d
3p
4p4s
3s
2s
1s
B(z = 5)
Begin filling 2pBegin filling 2p
2p
3d
3p
4p4s
3s
2s
1s
C(z = 6)
Electrons don’t like to pairElectrons don’t like to pair
2p
3d
3p
4p4s
3s
2s
1s
O(z = 8)
2p
3d
3p
4p4s
3s
2s
1s
F(z = 9)
2p
3d
3p
4p4s
3s
2s
1s
Ne(z = 10)
Filled 2p – neon unreactiveFilled 2p – neon unreactive
Shape of the periodic table Shape of the periodic table explained by orbital pictureexplained by orbital picture
2 groups 10
groups
14 groups
6 groups
Shells: echoes of the Bohr orbitsShells: echoes of the Bohr orbits
The orbitals with the same Principal The orbitals with the same Principal Quantum number (1,2,3 etc) are grouped Quantum number (1,2,3 etc) are grouped into shellsinto shells
Filled shells have special significanceFilled shells have special significance
The periodic lawThe periodic law
Ionization energy and the periodic lawIonization energy and the periodic law
Ionization energy is energy required to remove electron Ionization energy is energy required to remove electron from the neutral atomfrom the neutral atom