Problem 11 - Chemistry

Question

What noble-gas configurations are the following elements likely to adopt in reactions when they form ions? (a) \(\mathrm{Rb}\) (b) Ba (c) \(\mathrm{Ga}\) (d) \(\mathrm{F}\)

Step-by-Step Solution

Answer

(a) [Kr]; (b) [Xe]; (c) [Ar]; (d) [Ne].

Step 1: Identify the Element and Locate in Periodic Table

First, we need to understand the position of each element in the periodic table to determine its likely actions in ion formation. \( \text{Rb} \) is Rubidium, located in Group 1 (alkali metals). \( \text{Ba} \) is Barium, located in Group 2 (alkaline earth metals). \( \text{Ga} \) is Gallium, located in Group 13. \( \text{F} \) is Fluorine, located in Group 17 (halogens).

Step 2: Determine the Number of Electrons to Lose or Gain

Elements want to achieve a stable electron configuration, typically that of the nearest noble gas. \( \text{Rb} \) has 1 electron in its outer shell and will lose 1 electron to achieve the configuration of Krypton (\( \text{Kr} \)). \( \text{Ba} \) has 2, and will lose 2 electrons to also reach \( \text{Xe} \). \( \text{Ga} \) has 3 electrons in its outer shell and will lose 3 electrons to achieve the configuration of Argon (\( \text{Ar} \)). \( \text{F} \) needs to gain 1 electron to achieve the configuration of Neon (\( \text{Ne} \)).

Step 3: Write the Noble Gas Configurations

Using the information from the periodic table, write down the noble gas configurations: \( \text{Rb}^+ \) becomes [Kr], \( \text{Ba}^{2+} \) becomes [Xe], \( \text{Ga}^{3+} \) becomes [Ar], and \( \text{F}^- \) becomes [Ne].

Key Concepts

Ion Formation

Ion formation is a fundamental concept in chemistry. It describes the process by which atoms gain or lose electrons to form ions. Ions are charged particles that result when an atom loses or gains electrons to obtain a stable electron configuration. This often means achieving the electron configuration of the nearest noble gas.

• When an atom loses electrons, it becomes a positively charged ion, or cation.
• When an atom gains electrons, it becomes a negatively charged ion, or anion.

For example, Rubidium (Rb) and Barium (Ba) lose electrons and become cations because they want to adopt a noble-gas electron configuration. Meanwhile, Fluorine (F), which gains an electron, becomes an anion. This process is essential for understanding chemical bonding and reactions. Atoms strive for a full outer electron shell, similar to the stable electronic arrangement of noble gases.

Electron Configuration

Electron configuration pertains to the distribution of electrons in an atom's electron shell. It's essentially the "address" of an electron in terms of energy levels and sublevel occupancy. When elements react, they often alter their electron configuration in pursuit of stability.

Atoms are more stable when their outermost electron shell is full, mirroring the configuration of noble gases. This is achieved by either gaining, losing, or sharing electrons.

• For elements like Rb, Ba, and Ga, losing electrons achieves a configuration akin to the noble gas found at a previous period on the periodic table.
• Conversely, elements such as Fluorine gain electrons to resemble the electron configuration of the nearest noble gas in the next period.

With each movement of electrons, a new ion with a noble-gas-like electron configuration is formed. These configurations are not just theoretical; they dictate how elements interact and bond with one another.

Alkali Metals

The alkali metals are found in Group 1 of the periodic table. This includes elements like Rubidium (Rb). These metals are characterized by having one electron in their outermost shell. This single electron is more easily lost in reactions to achieve a noble-gas configuration, hence forming a cation with a +1 charge.

• Alkali metals are highly reactive because they readily lose this one electron.
• This reactivity increases down the group, as the outer electron is farther from the nucleus and thus less tightly held.

As the alkali metals lose their outer electron, they form stable cations that share the electron configuration with the nearest noble gas, providing them with chemical stability. Understanding the reactivities of alkali metals is crucial to predicting their behavior in chemical reactions.

Halogens

Halogens, found in Group 17 of the periodic table, include elements like Fluorine (F). These elements are characterized by having seven electrons in their valence shell. Unlike alkali metals, halogens are close to achieving a full outer shell and hence readily gain an electron to form anions with a -1 charge, achieving the noble-gas electron configuration.

• Halogens are highly reactive, particularly with alkali metals, to form ionic compounds.
• The reactivity of halogens decreases down the group, contrary to the trend observed in alkali metals.

Gaining that one electron transforms them into stable anions, possessing the electron configuration of the nearby noble gas. This property of halogens makes them essential in various chemical reactions, especially where electron transfer is involved.