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Chem11 04 Electron Config Notes01.doc
Chem 11
Electron Configuration Notes
Writing Electron Configuration for Neutral Atoms
2 simple rules;
1. As atomic number increases, electrons are added to the orbitals having the lowest
energy first ... this is to ensure the LOWEST POSSIBLE ENERGY.
2. A maximum of 2 electrons can be placed in each orbital.
Electron Configuration: is a description of which orbitals in an atom contain electrons
and how many electrons are in each orbital.
2 e
-
10 e
-
6 e
-
1s
2s
2p
3s
3p
4s 3d 4p
5s 4d 5p
6s 5d 6p
7s 6d 7p
4f
5f
Full Notation
Fill the electron from the lowest energy level first then continue filling until all electrons
have been placed. If unsure refer to the above orbital version of the periodic table and simply
fill electrons.
Notice that 4s fills before 3d, which fills before 4p orbital – refer to the periodic table above.
example H = (1s
1
) He = (1s
2
) Li = ( 1s
2
2s
1
) Be = (1s
2
2s
2
) B = (1s
2
2s
2
2p
1
)
O = (1s
2
2s
2
2p
4
) F = (1s
2
2s
2
2p
5
) Ne = (1s
2
2s
2
2p
6
)
Fe = (1s
2
2s
2
2p
6
3s
2
3p
6
4s
2
3d
6
) Se = (1s
2
2s
2
2p
6
3s
2
3p
6
4s
2
3d
10
4p
4
)
Core Notation
The set of electrons belonging to a given atom can be divided into two subsets: the CORE
electrons and the OUTER electrons.
core: of an atom is the set of electrons having the configuration of the nearest noble gas
(He, Ne, Ar, Kr, etc.) having an atomic number less than that of the atom being considered.
