Problem 57 - Chemistry: The Central Science in SI Units, Global Edition

Question

Each of the following elements is capable of forming an ion in chemical reactions. By referring to the periodic table, predict the charge of the most stable ion of each: (a) Be, (b) \(\mathrm{Rb}\), (c) As, \((\mathbf{d})\) In, (e) At.

Step-by-Step Solution

Answer

The most stable ions and their charges for the given elements are: (a) \(Be^{2+}\), (b) \(Rb^{+}\), (c) \(As^{3-}\), (d) \(In^{3+}\), and (e) \(At^{-}\).

Step 1: Identify the Group Number and Valence Electrons

Consult the periodic table to find the group number for each element. The group number helps us determine the number of valence electrons. (a) Be is in Group 2, so it has 2 valence electrons. (b) Rb is in Group 1, so it has 1 valence electron. (c) As is in Group 15, so it has 5 valence electrons. (d) In is in Group 13, so it has 3 valence electrons. (e) At is in Group 17, so it has 7 valence electrons.

Step 2: Predict the Charges of the Most Stable Ions

Next, predict the charge of the most stable ion for each element based on the valence electrons. (a) Be tends to lose 2 electrons to have a full outer shell, forming an ion with a \(+2\) charge: \(Be^{2+}\). (b) Rb tends to lose 1 electron to have a full outer shell, forming an ion with a \(+1\) charge: \(Rb^{+}\). (c) As tends to gain 3 electrons to have a full outer shell, forming an ion with a \(-3\) charge: \(As^{3-}\). (d) In tends to lose 3 electrons to have a full outer shell, forming an ion with a \(+3\) charge: \(In^{3+}\). (e) At tends to gain 1 electron to have a full outer shell, forming an ion with a \(-1\) charge: \(At^{-}\). The charges of the most stable ions for the given elements are: (a) \(Be^{2+}\) (b) \(Rb^{+}\) (c) \(As^{3-}\) (d) \(In^{3+}\) (e) \(At^{-}\)

Key Concepts

Valence Electrons

Valence electrons play a crucial role in chemical bonding and ion formation. These are the outermost electrons of an atom and are shared, gained, or lost during chemical reactions. By knowing an element's valence electrons, we can predict how it will interact with other atoms and form ions.

• Elements in the same group on the periodic table have the same number of valence electrons, which explains their similar chemical properties.
• For instance, Group 1 elements, such as Rb (Rubidium), have 1 valence electron, while Group 17 elements like At (Astatine) have 7.

When atoms form ions, they tend to achieve the electron configuration of the nearest noble gas, which is considered stable. For Rb, losing its single valence electron achieves the configuration of Krypton, resulting in a positive charge. On the other hand, elements like Astatine prefer to gain electrons to resemble the nearest noble gas, which is why At forms a an At^- ion.

Periodic Table

The periodic table is a systematic way of organizing all known elements based on their atomic number, electron configurations, and recurring chemical properties. It is divided into groups (vertical columns) and periods (horizontal rows). These divisions help categorize elements with similar characteristics.

• Groups reflect the number of valence electrons, such as Group 2 elements like Be (Beryllium) having 2 valence electrons.
• Periods show elements with increasing atomic numbers and electron shells, but the same number of valence electrons within a group.

Suppose you are examining the periodic table to determine the most stable ion. In that case, you'll notice a pattern where metals generally become positively charged ions (cations) by losing electrons. In contrast, non-metals gain electrons, becoming negatively charged ions (anions). For example, Indium (In) in Group 13, like other metals in its group, tends to lose electrons and form positive ions.

Stable Ions

In chemistry, achieving stability is an atom's goal, which often involves forming ions. Stable ions have full outer electron shells similar to noble gases, making them energetically favorable. This shift towards stability explains the typical charge of ions.

• Metals, usually found on the left side of the periodic table, tend to lose electrons to stabilize, resulting in cations. For example, Beryllium forms a stable Be²⁺ when it loses two electrons.
• Conversely, non-metals, generally located on the right side, gain electrons to become stable, forming anions. Astatine, for example, gains one electron to form the At^- anion.

Understanding how atoms or elements achieve their most stable ionic form through the gain or loss of electrons provides insight into their behavior in reactions. Knowing the number of valence electrons and the element's position on the periodic table allows us to predict these tendencies.