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Electron Configuration Notes for Chemistry Students, Slides of Chemistry

Rules and examples for writing electron configurations for neutral atoms and ions. It explains the concept of core and outer electrons, and provides exceptions for certain elements. Students are encouraged to create a table for elements p, ti, co, br, sr, ar, k, cd, ca, xe, cs, pb, ga, mn, and zr.

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2021/2022

Uploaded on 09/27/2022

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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.
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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.

Rules:

  1. Locate atom and note the noble gas at the end of row above the element.
  2. Place noble gas into square brackets [ ] and write the rest of the electron configuration.
  3. Exception : If you asked to write the core notation for a noble gas such as Kr, you must show the electron configuration as Kr ([Ar] 4s^2 3d^10 4p^6 ) Do not write Kr ([Kr])

Electron Configuration Exceptions

There are two exceptions to the configuration of elements up to Kr.

Expect Cr ([Ar] 4s^2 3d^4 )

Right WAY Cr ([Ar] 4s^1 3d^5 )

Expect Cu ([Ar] 4s^2 3d^9 )

Right WAY Cu ([Ar] 4s^1 3d^10 )

Filled or exactly half-filled d-subshell is especially stable.

Writing Electron Configurations for Ions

  1. Negative Ions: To write the electron configuration, add electrons to the last unfilled subshell, starting where the neutral atom left off.
  2. Positive Ions: Two Rules a. Electrons in outermost shell (largest n-value) are removed first. b. If there are electrons in both the s- and p-orbitals of the outermost shell, the electrons in the p-orbitals are removed first. c. Remove electrons in the order of p before s before d.

Questions;

On a separate sheet of paper make a 3 column table and label

Element Full Notation Core Notation P Ti

Then write out the notation for the following elements;

P, Ti, Co, Br, Sr, Ar, K, Cd, Ca, Xe, Cs, Pb, Ga, Mn, Zr