Question

Use condensed electron configurations and Lewis electrondot symbols to depict the ions formed from each of the following atoms, and predict the formula of their compound: (a) Cs and \(S\) (b) \(\mathrm{O}\) and \(\mathrm{Ga}\) (c) \(\mathrm{N}\) and \(\mathrm{Mg}\) (d) Br and Li

Short answer

Cs2S, Ga2O3, Mg3N2, LiBr

Step-by-step solution

Determine the electron configurations of the elements

Find the condensed electron configurations for each element: (a) Cs: [Xe] 6s^1 S: [Ne] 3s^2 3p^4(b) O: [He] 2s^2 2p^4 Ga: [Ar] 3d^10 4s^2 4p^1(c) N: [He] 2s^2 2p^3 Mg: [Ne] 3s^2(d) Br: [Ar] 3d^10 4s^2 4p^5 Li: [He] 2s^1

Determine the ions formed

Determine the ions formed by gaining or losing electrons to achieve a noble gas configuration:(a) Cs loses 1 electron: Cs^+: [Xe] S gains 2 electrons: S^2-: [Ar](b) O gains 2 electrons: O^2-: [Ne] Ga loses 3 electrons: Ga^3+: [Ar] 3d^10(c) N gains 3 electrons: N^3-: [Ne] Mg loses 2 electrons: Mg^2+: [Ne](d) Br gains 1 electron: Br^-: [Kr] Li loses 1 electron: Li^+: [He]

Predict the formulas of the compounds

Combine the ions to form neutral compounds:(a) Cs^+ and S^2-: Cs2S(b) O^2- and Ga^3+: Ga2O3(c) N^3- and Mg^2+: Mg3N2(d) Br^- and Li^+: LiBr

Represent the Lewis electron-dot symbols

Draw the Lewis electron-dot symbols for the ions(a) Cs^+ : Cs^+ (no dots) S^2- : [S]^{2-} with 8 dots(b) O^2- : [O]^{2-} with 8 dots Ga^3+ : Ga^{3+} (no dots)(c) N^3- : [N]^{3-} with 8 dots Mg^2+ : Mg^{2+} (no dots)(d) Br^- : [Br]^{-} with 8 dots Li^+ : Li^{+} (no dots)

Key concepts

Condensed Electron Configurations

Condensed electron configurations simplify the way we represent the electron arrangement in atoms by using noble gas notation. Instead of writing out every single electron, we use the configuration of the nearest previous noble gas as a shorthand.
For example, the condensed configuration for Cesium (Cs) is [Xe] 6s^1. Here, [Xe] represents the full electron configuration of Xenon, which Cs has in addition to one electron in the 6s orbital.
This makes it easier to identify the valence electrons involved in bonding and ion formation.
Some more examples are:

• Sulfur (S): [Ne] 3s^2 3p^4
• Oxygen (O): [He] 2s^2 2p^4
• Gallium (Ga): [Ar] 3d^{10} 4s^2 4p^1

With condensed electron configurations, predicting how atoms gain or lose electrons to form ions becomes straightforward.
It illustrates how they strive to achieve a stable noble gas configuration.

Lewis Electron-Dot Symbols

Lewis electron-dot symbols, or Lewis dot structures, use dots to represent valence electrons around an element's symbol.
These structures help visualize the electron arrangement in an atom and how they might participate in chemical bonding.
For example, a neutral sulfur (S) atom would be represented as S with six dots. Each dot stands for a valence electron.
When sulfur forms an ion (S^{2-}), it gains two extra electrons, resulting in eight dots around the symbol: [S]^{2-}.
Here are other examples:

• Cesium (Cs^+): Cs^+ (no dots since it loses one electron)
• Oxygen (O^{2-}): [O]^{2-} with eight dots
• Gallium (Ga^{3+}): Ga^{3+} (no dots, as it loses three electrons)

The Lewis electron-dot symbols provide a simple visual cue for understanding ion formation and electron transfer during chemical reactions.

Noble Gas Configuration

The noble gas configuration refers to the electron arrangement in noble gases, like Helium (He), Neon (Ne), and Argon (Ar).
These configurations are especially stable because noble gases have complete valence shells.
Atoms tend to gain or lose electrons to achieve a similar stable arrangement. This is evident when elements form ions.
For instance:

• Cesium (Cs) loses one electron to resemble Xenon (Xe): Cs^+: [Xe]
• Sulfur (S) gains two electrons to resemble Argon (Ar): S^{2-}: [Ar]
• Oxygen (O) gains two electrons to resemble Neon (Ne): O^{2-}: [Ne]

By adopting noble gas configurations, atoms reach a lower energy state, which is more stable.
This concept is crucial in understanding why and how ions form, and it bridges the gap between electronic structure and chemical reactivity.