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CHEM105-05

Chapter 8 (8.1 8.3)

2 - November - 2008

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Quantum numbers andatomic orbitals

Principle quantum number (n):

- referred to as principle shell

- only positive integers allowed

- higher numbers = higher energy level

Orbital angular momentum quantum number (l)

- referred to as subshell

- l= 0,1,2,(n-1) 0,1,2,3 = s,p,d,f

Magnetic quantum number (ml):

- determines orientation in space of orbitals in given type of subshell- can have any integral value from -lto +l

Electron spin quantum number (ms):

- describes motion of electron with respect to magnetic field it induces

- can have value of either +1/2 () or -1/2 ()

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Review of orbital sub-shells

sorbitals

spherical

1 per shell

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Review of orbital sub-shells

porbitals

barbell

3 per shell

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Review of orbital sub-shells

dorbitals

multiple

shapes

5 per shell

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orbital energy diagrams

in hydrogen atoms, all subshells of a principalshell are at the same energy level

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orbital energy diagrams

in multielectron atoms, various subshells of aprincipal shell are at different energy levels,but all orbitals within a subshell are at the

same energy level

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orbital energy diagrams

orbital energies depend on nand l, but not onml

lower nand lvalues = lower energies

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electron configurations

the way electrons are distributed among thevarious orbitals in the atom is called theelectron configurationof the atom

how we fill in the shells and subshells withelectrons

can be represented using spdf notationororbital diagrams

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electron configurations

example spdf notation

1s2

2s2

2p3

coefficients = n

letters = l superscripts = # of electrons in subshell

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electron configurations

example spdf notation

1s2

2s2

2p3

2 electrons in 1ssubshell

2 electrons in 2ssubshell

3 electrons in 2psubshell

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rules for electronconfigurations

1. electrons occupy orbitals of the lowest availableenergy level

E

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rules for electronconfigurations

1. electrons occupy orbitals of the lowest availableenergy level

1s, 2s, 3s, 3p, 4s, 3d, 4p, 5s, 4d, 5p, 6s, 4f, 5d, 6p, 7s

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rules for electronconfigurations

1. electrons occupy orbitals of the lowest availableenergy level

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rules for electronconfigurations

1. electrons occupy orbitals of the lowest availableenergy level

2. no two electrons in the same atom can have all 4

quantum numbers alike an atomic orbital can accommodate only 2 electrons, and

these electrons must have opposing spins

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rules for electronconfigurations

1. electrons occupy orbitals of the lowest availableenergy level

2. no two electrons in the same atom can have all 4

quantum numbers alike

3. in a group of orbitals of identical energy, electronsenter empty orbitals whenever possible

Hunds rule: 2 electrons carry identical charge and repel

each other, therefore electrons go into unoccupied orbitalsof lowest energy levels first

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aufbau principle

building up

building electron configurations by increasing

atomic number, and thus increasing electrons

ex: He electron configuration is just like H,with one more electron, Li is just like He, with

one more electron we just keep adding electrons using the rules

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in class activity

give the spdfand orbital diagramfor eachof the following atoms:

B F P Ca