Problem 19 - Chemistry The Central Science In Si Units

Question

Write the electron configuration for each of the following ions. and determine which ones possess noble-gas configurations: (a) \(\mathrm{Be}^{2+}\) (b) \(\mathrm{Mn}^{2+},(\mathbf{c}) \mathrm{Cd}^{2+}\) (d) \(\mathrm{Fe}^{3+}\), (e) \(\mathrm{Tl}^{+}\), (f) \(\mathrm{At}^{-}\).

Step-by-Step Solution

Answer

(a) Be²⁺ and (f) At⁻ achieve noble-gas configurations.

Step 1: Write Neutral Atom Configurations

First, write the electron configurations for the neutral atoms corresponding to each ion from the periodic table. - Beryllium (Be): **Configuration**: \(\text{Be: } 1s^2 2s^2\) - Manganese (Mn): **Configuration**: \(\text{Mn: } [Ar] 3d^5 4s^2\) - Cadmium (Cd): **Configuration**: \(\text{Cd: } [Kr] 4d^{10} 5s^2\) - Iron (Fe): **Configuration**: \(\text{Fe: } [Ar] 3d^6 4s^2\) - Thallium (Tl): **Configuration**: \(\text{Tl: } [Xe] 4f^{14} 5d^{10} 6s^2 6p^1\) - Astatine (At): **Configuration**: \(\text{At: } [Xe] 4f^{14} 5d^{10} 6s^2 6p^5\)

Step 2: Determine Ion Configurations

Next, remove (for cations) or add (for anions) the corresponding number of electrons to obtain the electron configurations of the ions. - \(\text{Be}^{2+}\): Remove two electrons **Configuration**: \(1s^2\) - \(\text{Mn}^{2+}\): Remove two electrons from 4s orbitals first **Configuration**: \[\text{Mn}^{2+}: [Ar] 3d^5\] - \(\text{Cd}^{2+}\): Remove two electrons from 5s orbitals **Configuration**: \[\text{Cd}^{2+}: [Kr] 4d^{10}\] - \(\text{Fe}^{3+}\): Remove three electrons; 2 from 4s orbital and 1 from 3d orbital **Configuration**: \[\text{Fe}^{3+}: [Ar] 3d^5\] - \(\text{Tl}^{+}\): Remove one electron from 6p orbital **Configuration**: \[\text{Tl}^{+}: [Xe] 4f^{14} 5d^{10} 6s^2\] - \(\text{At}^{-}\): Add one electron to 6p orbital **Configuration**: \[\text{At}^{-}: [Xe] 4f^{14} 5d^{10} 6s^2 6p^6\]

Step 3: Identify Noble-Gas Configurations

Compare the ion configurations to the noble-gas configurations to identify any matches.- Noble gases: - Helium (He): \(1s^2\) - Neon (Ne): \[1s^2 2s^2 2p^6\] - Argon (Ar): \[1s^2 2s^2 2p^6 3s^2 3p^6\] - Krypton (Kr): \[1s^2 2s^2 2p^6 3s^2 3p^6 4s^2 3d^{10} 4p^6\] - Xenon (Xe): \[1s^2 2s^2 2p^6 3s^2 3p^6 4s^2 3d^{10} 4p^6 5s^2 4d^{10} 5p^6\] - \(\text{Be}^{2+} ightarrow \ ext{He} (Noble gas)\)- \(\text{At}^{-} ightarrow \text{Rn} ([Xe] 4f^{14} 5d^{10} 6s^2 6p^6) \ ext{(Noble gas)}\) Only \(\text{Be}^{2+} \ ext{and } \text{At}^{-}\) ions have full noble-gas configurations.

Key Concepts

Noble-Gas Configuration

Noble-gas configuration refers to the arrangement of electrons in an atom or ion that mirrors the electron arrangement of the inert or noble gases. Noble gases, like helium (He), neon (Ne), and argon (Ar), have full outer electron shells. The stability of these full electron shells contributes to the inert nature of noble gases, meaning they do not readily engage in chemical reactions.
Understanding noble-gas configuration is crucial for identifying whether a particular ion has attained a stable electron state akin to that of a noble gas. This is accomplished by either losing or gaining electrons to fill or empty the outermost electron shell.

• For instance, a beryllium ion (Bʰ̞̟͆ʰ̟̇ʰ̟̇دهBʰ̞̟͆), which loses 2 electrons (configuration: Bʰ̞̟͆), reaches the configuration of helium (Bʰ̞̟͆), a noble gas.
• Astatine ion (Bʰ̞̟͆ʰ̟̇دهBʰ̞̟͆), by gaining 1 electron, achieves the configuration of radon (Bʰ̞̟͆Bʰ̞̟͆), another noble gas.

Acquiring a noble-gas configuration usually increases an element's stability and explains why ion formation often results in noble-gas-like configurations.

Ion Electron Configuration

Ion electron configuration involves determining the correct arrangement of electrons when an atom loses or gains electrons to form an ion. When an atom becomes an ion, it loses its neutral charge due to the loss or gain of electrons, which are negatively charged. To find the electron configuration of an ion, you must adjust the electron count according to its charge.

• For cations (positively charged ions like Bʰ̞̟͆), you remove electrons. For example, Bʰ̞̟͆ (formed from Bʰ̞̟͆ʰ̟̇بʜ̿̓) involves removing 2 electrons from Bʰ̞̟͆ as shown: Bʰ̞̟͆ Bʰ̞̟͆
• Conversely, anions (negatively charged ions, such as Bʰ̞̟͆) gain electrons. For Bʰ̞̟͆, an electron is added to Bʰ̞̟͆, leading to the altered configuration Bʰ̞̟͆.

By comparing the ion's electron configuration to neutral atoms, you can determine if it matches a noble-gas configuration, reflecting greater stability.

Periodic Table

The periodic table is an essential tool for understanding the properties of elements and their electron configurations. Each element is placed according to its atomic number, and its position gives insights into its chemical properties and the likely electron configuration. The arrangement of the periodic table into periods and groups corresponds to the filling of electron shells and subshells.
When dealing with electron configurations, the periodic table helps predict both the configuration of neutral atoms and the resulting configurations of ions:

• As you move across a period, electrons are added one by one, filling the subshells in the order of increasing energy levels (like 1s, 2s, 2p, etc.).
• The vertical groups, on the other hand, share similar chemical traits, resulting from having a similar valence shell electron configuration.

By knowing the position of an element on the periodic table, you can efficiently write its electron configuration and understand how it will form ions. This is pivotal for understanding whether an ion attains a noble-gas configuration upon losing or gaining electrons.