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Electron Configurations. 4.3. Pauli Exclusion Principle. No more than two e- can occupy a single orbital at a time e- spin in opposite directions Spin quantum number can be +½ or -½ . Electron Configuration. A description of the electron orbitals in an atom.
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Pauli Exclusion Principle • No more than two e- can occupy a single orbital at a time • e- spin in opposite directions • Spin quantum number can be +½ or -½
Electron Configuration • A description of the electron orbitals in an atom
e- occupy lower energy levels first • Aufbau principle – electrons in an atom will occupy the lowest energy orbitals available.
Electron Configurations • Remember, the smaller the principal quantum number, the lower the energy, and the smaller the l quantum number, the lower the energy
Electron Configurations • The order in which energy levels fill is … 1s<2s<2p<3s<3p
Electron Configurations • After this, the energy levels are less straightforward • The E levels of the 3d orbitals are slightly higher than those of the 4s orbitals. 1s<2s<2p<3s<3p<4s≈3d
Electron Configurations • The next irregularity is 5s and 4d are close in energy 1s<2s<2p<3s<3p<4s≈3d<4p<5s≈4d • Still more irregularities exist with higher energy orbitals.
Rules for Writing e- Configs • Determine the # of e- the atom has (atomic #) Fluorine as an example has 9 electrons
Rules for Writing e- Configs • Fill orbitals in order of increasing energy (follow the diagram on the next slide) S orbital – 2 e- P orbitals – 6 e- D orbitals – 10 e- F orbitals – 14 e-
Rules for Writing e- Configs • The configuration for F is 1s22s22p5 • Make sure the total number of e- in the config match the atomic number
Electron Configurations • Tells us how the 16 e- of S are configured • The electron configuration for S is • S=1s22s22p63s23p4 • Each s orbital has 2 e-, each p orbital can have 6 e- (2 per orbital)
Electron Configurations • Do the electron configurations for the following elements… • O, Ar, Ca, V, Sr, and Sn • Remember the d orbital is off by 1 E level
The f orbital • If you end in the f orbital – make sure you indicate d1 first. • If you go through the f orbital, count the s orbital, then all of the f then go to d and beyond.
Electron Configurations • There are still some irregularities with higher energy orbitals. • Chromium is an example of this • Cr =1s22s22p63s23p64s13d5 • There is one unfilled d orbital and a filled s orbital
Electron Configurations • There are e- configs listed in the p.t. in the back of your book. • These are the ground state configs of the isolated atoms in the gas phase. • Under other conditions, the configs could be different
Orbital Diagrams • Hund’s Rule says the maximum stability for e- is when you have the maximum number of unpaired electrons when they have the same quantum number.
Orbital Diagrams • Use boxes to show e- location • Boron = 1s22s22p1 • The orbital diagram looks like… { 2s 1s 2p
Orbital Diagrams • What is the Carbon orbital diagram. • The config is 1s22s22p63s2
Electron Configurations • To save space, some configurations are written like • S = [Ne]3s23p4 • This means take neon’s configuration and add 3s23p4 to the end of it.
