Question

The following electron configurations represent excited states. Identify the element, and write its ground-state condensed electron configuration. (a) \(\mathrm{ls}^{2} 2 s^{2} 3 p^{2} 4 p^{1}\), (b) \([\operatorname{Ar}] 3 d^{10} 4 s^{1} 4 p^{4} 5 s^{1}\), (c) \([\operatorname{Kr}] 4 d^{6} 5 s^{2} 5 p^{1}\).

Short answer

The elements and their ground-state condensed electron configurations are: (a) Nitrogen (N): \(\mathrm{1s^{2} 2s^{2} 2p^{3}}\) (b) Selenium (Se): \([\operatorname{Ar}] 3 d^{10} 4 s^{2} 4 p^{4}\) (c) Rhodium (Rh): \([\operatorname{Kr}] 4d^{5} 5s^{1}\)

Step-by-step solution

Identify the elements

To identify the elements, find the total number of electrons in the excited configurations. (a)\(\mathrm{ls}^{2} 2 s^{2} 3 p^{2} 4 p^{1}\)\\ Total number of electrons = 2 + 2 + 2 +1 = 7, which is Nitrogen (N). (b) \([\operatorname{Ar}] 3 d^{10} 4 s^{1} 4 p^{4} 5 s^{1}\)\\ Argon has 18 electrons, so total number of electrons = 18 +10 +1 + 4+ 1 = 34, which is Selenium (Se). (c) \([\operatorname{Kr}] 4 d^{6} 5 s^{2} 5 p^{1}\)\\ Krypton has 36 electrons, so total number of electrons = 36+6 +2 + 1=45, which is Rhodium (Rh).

Write the ground-state condensed electron configurations

(a) Nitrogen (N), with 7 electrons, has the following ground-state configuration: \(\mathrm{1s^{2} 2s^{2} 2p^{3}}\). (b) Selenium (Se), with 34 electrons, has the following ground-state configuration: \([\operatorname{Ar}] 3 d^{10} 4 s^{2} 4 p^{4}\). (c) Rhodium (Rh), with 45 electrons, has the following ground-state configuration: \([\operatorname{Kr}] 4d^{5} 5s^{1}\).

Key concepts

Excited States

In atomic physics, an excited state of an atom occurs when one or more of its electrons are in an energy level higher than the lowest possible energy levels, known as ground states. Electrons in atoms can be excited to these higher energy levels in a variety of ways, including absorption of photons or collisions with other particles. An excited state has more energy and is generally less stable than the ground state.

For example, in the electron configuration \(1s^2 2s^2 3p^2 4p^1\), an electron from a lower energy level has been moved up to a higher level (4p). This creates an excited state since it's not the lowest possible energy arrangement for the electrons. Identifying these excited states can help us understand the processes that atoms undergo when they absorb energy.

Ground-State Condensed Configuration

The ground-state electron configuration of an atom is its most stable arrangement, where all electrons are in the lowest possible energy levels. When electrons are in the ground state, there are no electrons in "excited" orbitals, meaning each is as close to the nucleus as the quantum mechanical rules allow.

For example, the ground-state configuration for nitrogen (N) with 7 electrons is \(1s^2 2s^2 2p^3\). This arrangement represents the electrons occupying the lowest energy orbitals available. In contrast to excited states, the ground-state does not have electrons elevated to higher energy levels when lower energy levels are not completely filled. This makes the atom in the ground state more stable compared to when it’s in an excited state.

Periodic Table Elements

The periodic table is a systematic arrangement of elements based on atomic numbers and their electron configurations. Each element on the periodic table is defined by its atomic number, which equals the number of protons and, in a neutral atom, also the number of electrons.

In the context of the exercise:

• Nitrogen (N) has 7 electrons and is situated in Group 15 of the periodic table.
• Selenium (Se) with 34 electrons, is located in Group 16, a group known for its chemical reactivity due to having six valence electrons.
• Rhodium (Rh), with 45 electrons, is found in Group 9, known for its use in catalytic converters and jewelry.

The periodic table helps predict the ground-state configuration of elements and provides insights into their chemical properties and behavior.

Electron Counting

Electron counting involves determining the number of electrons present in an atom or ion. This is essential in identifying elements from their electron configurations and understanding how elements will interact with each other chemically.

In the provided exercise, electron counting was used to determine the true identity of the element given its excited electron configuration. For example:

• With a configuration \(1s^2 2s^2 3p^2 4p^1\), counting gives a total of 7 electrons, matching nitrogen.
• The configuration \([Ar] 3d^{10} 4s^1 4p^4 5s^1\) totals 34 electrons, corresponding to selenium.
• For \([Kr] 4d^6 5s^2 5p^1\), counting leads to 45 electrons, which is rhodium.

Properly counting electrons helps ensure the correct identification of elements in various states and configurations.