1.9: Electron Configurations for Transition Metal Elements

Estimated Time to Read: 6 min

Basic Steps

Writing an electron configuration for a transition metal element follows the same basic steps as for writing an electron configuration for an element in the s-block or p-block. List each subshell, and then fill each subshell with an appropriate number of electrons until all electrons in the element are accounted for. Transition elements have electrons in the d orbital, which introduces some additional nuance in the electron configurations. First, recall that the n = 3 shell is the first shell to have a d subshell. Second, recall that the 4s subshell is lower in energy than the 3d subshell. Thus, when filling electrons into orbitals the correct order of filling is 1s² 2s² 2p⁶ 3s² 3p⁶ 4s² 3d¹⁰ 4p⁶. Similarly, the 5s will be filled before the 4d, and the 6s will be filled before the 5d.

Some elements in the d block will also have electrons in the f subshell. The n = 4 shell is the first shell to have a f subshell. Thus, the 6s subshell is lower in energy than the 4f subshell, and the correct order of filling is 1s² 2s² 2p⁶ 3s² 3p⁶ 4s² 3d¹⁰ 4p⁶ 5s² 4d¹⁰ 5p⁶ 6s² 4f¹⁴ 5d¹⁰ 6p⁶. Similarly, the 7s will be filled before the 5f, which will be filled before the 6d subshell.

Example \(\PageIndex{1}\)

Write the ground state electron configuration for vanadium (V).

Solution: Method 1

1. Find the number of electrons in the atom: Vanadium has 23 electrons.
2. List the subshells following the model shown in Figure 1.6.3: 1s 2s 2p 3s 3p 4s 3d
3. Fill the subshells until all electrons have been accounted for. Remember: each s subshell can hold 2 electrons, each p subshell can hold six electrons, each d subshell can hold 10 electrons, and each f subshell can hold 14 electrons: 1s² 2s² 2p⁶ 3s² 3p⁶ 4s² 3d³

Solution: Method 2

1. Locate the atom on the periodic table.

   

   Figure \(\PageIndex{1}\): Periodic table of the elements with the location of vanadium (V) highlighted. (CC-BY-NC-SA; Kathryn A. Newton)

2. Starting at hydrogen and the 1s subshell, read across each row of the periodic table until you get to your chosen element. As you read across each row, list each subshell and the number of electrons in the subshell.

   

   Figure \(\PageIndex{2}\): Periodic table of the elements with the 1s² subshell highlighted. V has two electrons in the 1s subshell. (CC-BY-NC-SA; Kathryn A. Newton)

   

   Figure \(\PageIndex{3}\): Periodic table of the elements with the 2s² subshell highlighted. V has two electrons in the 2s subshell. (CC-BY-NC-SA; Kathryn A. Newton)

   

   Figure \(\PageIndex{4}\): Periodic table of the elements with the 2p⁶ subshell highlighted. V has six electrons in the 2p subshell. (CC-BY-NC-SA; Kathryn A. Newton)

   

   Figure \(\PageIndex{5}\): Periodic table of the elements with the 3s² subshell highlighted. V has two electrons in the 3s subshell. (CC-BY-NC-SA; Kathryn A. Newton)

   

   Figure \(\PageIndex{6}\): Periodic table of the elements with the 3p⁶ subshell highlighted. V has six electrons in the 3p subshell. (CC-BY-NC-SA; Kathryn A. Newton)

   

   Figure \(\PageIndex{7}\): Periodic table of the elements with the 4s² subshell highlighted. V has two electrons in the 4s subshell. (CC-BY-NC-SA; Kathryn A. Newton)

   

   Figure \(\PageIndex{8}\): Periodic table of the elements with the 3d³ subshell highlighted. V has three electrons in the 3d subshell. (CC-BY-NC-SA; Kathryn A. Newton)

3. Combine the list into a single electron configuration. V's electron configuration is 1s² 2s² 2p⁶ 3s² 3p⁶ 4s² 3d³ or [Ar] 4s² 3d³

Example \(\PageIndex{2}\)

Write the ground state electron configuration for osmium (Os).

Solution

Figure \(\PageIndex{9}\): Periodic table of the elements showing the construction of the electron configuration of osmium (Os). (CC-BY-NC-SA; Kathryn A. Newton)

Exceptions to Expected Electron Configurations

There are some exceptions to the order of filling of orbitals that is shown in Figure 1.6.1. For example, the electron configurations of the transition metals chromium (Cr) and copper (Cu), are not those we would expect. Rather, Cr and Cu take on half-filled and fully-filled 3d configurations.

The electron configuration of chromium (Cr) includes a half-filled 3d subshell.

Cr: 1s² 2s² 2p⁶ 3s² 3p⁶ 4s¹ 3d⁵

The electron configuration of copper (Cu) includes a fully-filled 3d subshell.

Cu: 1s² 2s² 2p⁶ 3s² 3p⁶ 4s¹ 3d¹⁰

The actual electron configuration of these elements may be rationalized in terms of an added stability associated with a half-filled (ns¹, np³, nd⁵, nf⁷) or filled (ns², np⁶, nd¹⁰, nf¹⁴) subshell. In fact, this "special stability" is really another consequence of the instability caused by pairing an electron with another in the same orbital. (There are repulsive forces between two electrons in the same orbital.) Recall the small differences in energy between higher energy subshells. In the case of Cr, the repulsive forces between two electrons in the 4s would be greater than the energy gained by shifting an electron into the 3d. Thus, the added stability is enough to shift an electron from one orbital to another. In the case of Cu, the repulsive forces between two electrons in the 4s orbital is greater than between two electrons paired in a 3d orbital so one electron is shifted from the 4s to the 3d. In heavier elements, other more complex effects can also be important and lead to many additional anomalies. For example, cerium has an electron configuration of [Xe]6s²4f¹5d¹, which is impossible to rationalize in simple terms. In most cases, however, these apparent anomalies do not have important chemical consequences. Figure \(\PageIndex{10}\) indicates which elements have a non-standard configuration.

Figure \(\PageIndex{10}\): Periodic table of the elements. The highlighted elements have a non-standard electron configuration. (CC-BY-NC-SA; Kathryn A. Newton)

Electron Configuration of Transition Metals: Electron Configuration of Transition Metals, YouTube(opens in new window) [youtu.be]

Electron Configurations of Transition Metal Ions

Transition metal elements are unique in the sense that they can have multiple oxidation states. While negative oxidation states are possible for some transition metal elements, we will focus on the positive oxidation states, which are more common.

Writing an electron configuration for a transition metal ion starts with the same steps as writing the configuration of an s- or p-block cation: Write the electron configuration for the neutral atom and then determine the number of electrons that are lost to form the cation. The electrons will be removed from the highest energy shell in the neutral configuration. This means that electrons will be removed from the 4s subshell before any electrons are removed from the 3d subshell, and similarly electrons will be removed from the 5s subshell before they are removed from the 4d subshell. If the highest energy s subshell is empty, then additional electrons will be removed from the highest energy d subshell.

Example \(\PageIndex{3}\)

Write an electron configuration for V⁴⁺.

Solution

1. Write the configuration of the neutral atom. V: 1s² 2s² 2p⁶ 3s² 3p⁶ 4s² 3d³
2. Determine how many electrons were lost. V⁴⁺ was formed by the loss of four electrons.
3. Remove electrons from the highest shell, starting with the highest energy subshell.

V⁺: 1s² 2s² 2p⁶ 3s² 3p⁶ 4s¹ 3d³

V²⁺: 1s² 2s² 2p⁶ 3s² 3p⁶ 4s⁰ 3d³

V³⁺: 1s² 2s² 2p⁶ 3s² 3p⁶ 4s⁰ 3d²

V⁴⁺: 1s² 2s² 2p⁶ 3s² 3p⁶ 4s⁰ 3d¹, which is typically written as 1s² 2s² 2p⁶ 3s² 3p⁶ 3d¹ or [Ar] 3d¹

Problems

Exercise \(\PageIndex{1}\)

Write the expanded and shortened ground state electron configuration for nickel (Ni).

Answer

Expanded: 1s² 2s² 2p⁶ 3s² 3p⁶ 4s² 3d⁸

Noble Gas: [Ar] 4s² 3d⁸

Exercise \(\PageIndex{2}\)

Write the expanded and shortened ground state electron configuration for rhodium (Rh).

Answer

Expanded: 1s² 2s² 2p⁶ 3s² 3p⁶ 4s² 3d¹⁰ 4p⁶ 5s² 4d⁷

Noble Gas: [Kr] 5s² 4d⁷

Exercise \(\PageIndex{3}\)

Write the ground state electron configuration for Ni²⁺.

Answer

Neutral Ni: 1s² 2s² 2p⁶ 3s² 3p⁶ 4s² 3d⁸

Ni²⁺: 1s² 2s² 2p⁶ 3s² 3p⁶ 3d⁸ or [Ar] 3d⁸

Exercise \(\PageIndex{4}\)

Write the ground state electron configuration for Rh³⁺.

Answer

Neutral Rh: 1s² 2s² 2p⁶ 3s² 3p⁶ 4s² 3d¹⁰ 4p⁶ 5s² 4d⁷

Rh³⁺: 1s² 2s² 2p⁶ 3s² 3p⁶ 4s² 3d¹⁰ 4p⁶ 4d⁶ or [Kr] 4d⁶

Exercise \(\PageIndex{1}\)

Osmium is stable with oxidation states of +2, +3, +4, and +8. Write the electron configuration for Os²⁺ and Os³⁺.

Answer

Neutral Os: 1s² 2s² 2p⁶ 3s² 3p⁶ 4s² 3d¹⁰ 4p⁶ 5s² 4d¹⁰ 5p⁶ 6s² 4f¹⁴ 5d⁶

Os²⁺: 1s² 2s² 2p⁶ 3s² 3p⁶ 4s² 3d¹⁰ 4p⁶ 5s² 4d¹⁰ 5p⁶ 6s⁰ 4f¹⁴ 5d⁶ or [Xe] 4f¹⁴ 5d⁶

Answer

Os³⁺: 1s² 2s² 2p⁶ 3s² 3p⁶ 4s² 3d¹⁰ 4p⁶ 5s² 4d¹⁰ 5p⁶ 6s⁰ 4f¹⁴ 5d⁵ or [Xe] 4f¹⁴ 5d⁵

References

1. Petrucci, Ralph. Harwood, William. Herring, Geoffrey. Madura, Jeffery. General Chemistry: Principles and Modern Applications, 9th Edition. Pearson Education, Inc. New Jersey, 2007.
2. Hein, et al. Introduction to General, Organic, and Biochemistry. 9th ed. Hoboken, NJ 2009.

Contributors

• Liza Chu (UCD)