How do you write the electron configuration for sodium using noble gas notation?

Sodium has 11 electrons with a core electron configuration identical to neon. The condensed configuration is written as [Ne]3s1, where [Ne] represents the neon core electrons and 3s1 represents the single valence electron in the 3s orbital. This notation emphasizes that sodium's valence shell resembles other alkali metals.

Why does potassium's nineteenth electron enter the 4s orbital instead of the 3d orbital?

The 4s subshell has substantial penetrating ability and lower energy than the 3d subshell, which lacks radial nodes and experiences greater shielding from the nucleus. According to the aufbau principle, electrons fill lower-energy orbitals first, so potassium's configuration is [Ar]4s1 rather than [Ar]3d1.

What are valence electrons and core electrons in an atom?

Valence electrons occupy the outermost shell orbitals with the highest principal quantum number and determine chemical properties. Core electrons occupy inner shell orbitals and correspond to noble gas configurations. For sodium, the single 3s electron is valence; the 1s2 2s2 2p6 electrons are core.

Why do chromium and copper deviate from the aufbau principle?

Chromium and copper achieve extra stability through half-filled and completely filled d subshells. Chromium has [Ar]4s1 3d5 instead of [Ar]4s2 3d4, while copper has [Ar]4s1 3d10 instead of [Ar]4s2 3d9. Electrons shift from the 4s to 3d orbital to gain this preferred stability.

How do orbital energies differ between the 4s and 3d subshells in transition elements?

In transition elements, the 3d and 4s subshells have similar energies, making their relative order unpredictable. The 4s subshell typically fills first due to greater penetration, but the small energy gap allows electrons to shift between orbitals. This proximity explains why exceptions to the aufbau principle occur frequently in transition metals.

What is the electron configuration of cerium, and why is it unusual?

Cerium has the configuration [Xe]6s2 4f1 5d1 instead of the expected [Xe]6s2 4f2. This deviation occurs because the 6s, 4f, and 5d subshells are unusually close in energy. Electron-electron repulsions in the 4f orbital are larger than the small energy gaps between subshells, making the half-filled 4f and 5d configuration more stable.

How do you use noble gas cores to abbreviate electron configurations?

Noble gas cores represent filled inner shell electrons matching the preceding noble gas in the periodic table. For any element, write the noble gas symbol in brackets followed by the valence electron configuration. For example, lithium is [He]2s1 and aluminum is [Ne]3s2 3p1, emphasizing similarities within chemical families.

7.15

Electron Configuration of Multielectron Atoms

62.3K views03:26 min

The Pauli exclusion principle, Hund’s rule of maximum multiplicity, and the aufbau principle can be extended to envisage the electron configuration of any element.

Consider writing the electron configuration for sodium. The core electron distribution in sodium is exactly that of the preceding element, neon. The single valence electron occupies the 3s orbital.

Neon belongs to the eighteenth column of the periodic table — the noble gases. The electron configurations of these elements facilitate the condensed depiction of the electron configuration for other elements. For any element, the core electron configuration is the same as that of the noble gas that precedes it in the periodic table.

The electron configuration of sodium, for example, can be written as neon core, 3s¹.

The core electron configuration of potassium is 1s²2s²2p⁶3s² 3p⁶, leaving one valence electron. Now, does the nineteenth electron enter the 3d subshell?

Recall that the 4s subshell has substantial penetrating ability, which often leads to it having a lower energy than the 3d subshell does. The aufbau principle, therefore, would hold that the 4s subshell fills prior to the 3d subshell. The core of the preceding noble gas, argon, is used to write the condensed configuration.

Although these principles provide a starting point, the actual electron configurations must be confirmed experimentally. In several elements among the transition elements, lanthanides, and actinides, the orbital energies are in a different relative order, and the aufbau principle may not be completely followed.

In the transition elements, the 3d and 4s subshells have similar energies. The 4s subshell is often filled completely. For example, in scandium, the electron configuration is argon core, 4s² 3d¹. In zinc, the 4s and 3d subshells are filled to their maximum capacities.

However, the ground states of some metals, such as chromium and copper, have singly occupied 4s orbitals. Chromium is particularly notable because two subshells are partially filled, which deviates from the aufbau principle.
Across the lanthanide series, extending through cerium to lutetium, the 6s and 4f subshells have similar energies. The electron configuration for neodymium is xenon core, 6s²4f⁴.

Meanwhile, cerium has an unusual electron configuration of xenon core, 6s² 4f¹ 5d¹ because its 6s, 4f, and 5d subshells are unusually close in energy.

$$\rightleftharpoonup{xx}$$ $$\longleftharp{xx}$$, $$\longrightharp{xx}$$,

The alkali metal sodium (atomic number 11) has one more electron than the neon atom. This electron must go into the lowest-energy subshell available,…