Question

Write electron configurations for the following ions, and determine which have noble-gas configurations: (a) \(\mathrm{Cr}^{3+}\), (b) \(\mathrm{N}^{3-},(\mathrm{c}) \mathrm{Sc}^{3+},(\mathrm{d}) \mathrm{Cu}^{2+}\) (e) \(\mathrm{Tl}^{+}\), (f) \(\mathrm{Au}^{+}\).

Short answer

The electron configurations for the given ions are: (a) \(\mathrm{Cr}^{3+}\): \(1s²2s²2p⁶3s²3p⁶3d³\) (Not a noble-gas configuration) (b) \(\mathrm{N}^{3-}\): \(1s²2s²2p⁶\) (Noble-gas configuration) (c) \(\mathrm{Sc}^{3+}\): \(1s²2s²2p⁶3s²3p⁶\) (Noble-gas configuration) (d) \(\mathrm{Cu}^{2+}\): \(1s²2s²2p⁶3s²3p⁶3d¹⁰\) (Noble-gas configuration) (e) \(\mathrm{Tl}^{+}\): \(1s²2s²2p⁶3s²3p⁶4s²3d¹⁰4p⁶5s²4d¹⁰5p⁶6s²5d¹⁰6p⁵\) (Noble-gas configuration) (f) \(\mathrm{Au}^{+}\): \(1s²2s²2p⁶3s²3p⁶4s²3d¹⁰4p⁶5s²4d¹⁰5p⁶6s¹4f¹⁴5d⁹\) (Not a noble-gas configuration) The ions with noble-gas configurations are: \(\mathrm{N}^{3-}\), \(\mathrm{Sc}^{3+}\), \(\mathrm{Cu}^{2+}\), and \(\mathrm{Tl}^{+}\).

Step-by-step solution

(a) Determine electron configuration for \(\mathrm{Cr}^{3+}\)

First, we need to find the atomic number of Chromium (Cr). From the periodic table, Cr has an atomic number of 24. In its neutral state, it has the same number of electrons; therefore, the electron configuration for Cr is: 1s²2s²2p⁶3s²3p⁶4s²3d⁵ However, Cr⁺³ has lost three electrons. When an atom loses electrons, the first electrons to be removed are from the highest energy level, which is 4s in this case. Thus, the electron configuration for Cr³⁺ is: 1s²2s²2p⁶3s²3p⁶3d³

(a) Identify if the electron configuration for \(\mathrm{Cr}^{3+}\) is noble-gas

Comparing this electron configuration with the noble gas configurations, we notice that it is not a noble-gas configuration because it does not end with a full set of 2, 8, 18, 32, etc. electrons in each shell or subshell.

(b) Determine the electron configuration for \(\mathrm{N}^{3-}\)

The atomic number of Nitrogen (N) is 7. So, the electron configuration for N is: 1s²2s²2p³ As the ion is N³⁻, it means it has gained three extra electrons (total of 10 electrons). So, the new electron configuration for \(\mathrm{N}^{3-}\) is: 1s²2s²2p⁶

(b) Identify if the electron configuration for \(\mathrm{N}^{3-}\) is noble-gas

Comparing this electron configuration with the noble gas configurations, we notice that it has a noble-gas configuration, which is the same as Neon (Ne). Perform similar tasks for the given ions:

(c) Determine electron configuration for \(\mathrm{Sc}^{3+}\)

1s²2s²2p⁶3s²3p⁶4s²3d¹

(c) Identify if the electron configuration for \(\mathrm{Sc}^{3+}\) is noble-gas

It has a noble-gas configuration, which is the same as Argon (Ar).

(d) Determine electron configuration for \(\mathrm{Cu}^{2+}\)

1s²2s²2p⁶3s²3p⁶4s¹3d¹⁰

(d) Identify if the electron configuration for \(\mathrm{Cu}^{2+}\) is noble-gas

It has a noble-gas configuration, which is the same as Argon (Ar).

(e) Determine electron configuration for \(\mathrm{Tl}^{+}\)

1s²2s²2p⁶3s²3p⁶4s²3d¹⁰4p⁶5s²4d¹⁰5p⁶6s²5d¹⁰6p⁵

(e) Identify if the electron configuration for \(\mathrm{Tl}^{+}\) is noble-gas

It has a noble-gas configuration, which is the same as Xenon (Xe).

(f) Determine electron configuration for \(\mathrm{Au}^{+}\)

1s²2s²2p⁶3s²3p⁶4s²3d¹⁰4p⁶5s²4d¹⁰5p⁶6s¹4f¹⁴5d⁹

(f) Identify if the electron configuration for \(\mathrm{Au}^{+}\) is noble-gas

It does not have a noble-gas configuration. So, the ions with noble-gas configurations are: \(\mathrm{N}^{3-}\), \(\mathrm{Sc}^{3+}\), \(\mathrm{Cu}^{2+}\), and \(\mathrm{Tl}^{+}\).

Key concepts

Noble-Gas Configuration

A noble-gas configuration is an electron arrangement that mirrors the stable structure of a noble gas. These are the gases like Helium, Neon, and Argon, which have full outer electron shells. Having a complete outer shell is associated with maximum stability.

Noble-gas configurations make atoms less reactive. Elements tend to gain or lose electrons to achieve this stable arrangement. For example, when \(\mathrm{N}^{3-}\) gains three electrons, its configuration mimics that of Neon: \(\mathrm{1s}^2 2s^2 2p^6\).

Understanding which ions have noble-gas configurations helps predict their stability and reactivity. In the given exercise, \(\mathrm{N}^{3-}, \mathrm{Sc}^{3+}, \mathrm{Cu}^{2+}, and \mathrm{Tl}^{+}\) all have noble-gas configurations.

Ions

Ions are atoms or molecules that have gained or lost electrons, resulting in a net charge. When an atom gains electrons, it becomes negatively charged and is called an anion. If it loses electrons, it becomes positively charged, known as a cation.

For instance, \(\mathrm{Cr}^{3+}\) is a cation. It originally has 24 electrons, but after losing 3 electrons, it ends up with 21. Understanding ion formation is essential in determining their electron configurations.

• Anions, like \(\mathrm{N}^{3-}\), gain electrons and often achieve noble-gas configurations.
• Cations may or may not reach noble-gas configurations, depending on how many electrons are lost.

Periodic Table

The periodic table is a crucial tool for predicting elements' properties, including electron configurations. It arranges elements in increasing atomic numbers and groups with similar properties.

Each element's position tells you about its electron configuration, especially the arrangement of electrons in the outermost shells. For example, Chromium (Cr) in group 6 has its electrons spread over several sub-levels: \(\mathrm{1s^2 2s^2 2p^6 3s^2 3p^6 4s^1 3d^5}\).

Looking at the periodic table allows you to deduce the changes in electron configurations when elements form ions. Reading group numbers can help predict the number of electrons lost or gained for elements to reach a noble-gas configuration.

Electron Configuration Steps

Writing electron configurations involves understanding the order in which electrons fill subshells, based on increasing atomic number. Electrons fill orbitals starting from the lowest energy (1s) and move to higher energies.

Here's a basic layout:

• 1s is filled first, followed by 2s, 2p, 3s, 3p, 4s, and then 3d.
• Higher atomic numbers fill electrons in a more complex sequence, but the basic pattern repeats periodically.

For ions, remember:

• Electrons are added to the lowest available energy level for anions.
• Electrons are removed from the highest occupied energy level for cations.

Let’s consider \(\mathrm{Cu}^{2+}\). It loses two electrons, resulting in the configuration \(\mathrm{1s^2 2s^2 2p^6 3s^2 3p^6 3d^{10}}\), which is a noble-gas configuration.