Question

The most common charge associated with selenium is \(2-\). Indicate the chemical formulas you would expect for compounds formed between selenium and (a) barium, (b) lithium, (c) aluminum.

Short answer

(a) BaSe, (b) Li2Se, (c) Al2Se3.

Step-by-step solution

Determine the Charge of Selenium

Selenium commonly forms an anion with a charge of \(2-\), written as \(\text{Se}^{2-}\). This is because selenium gains two electrons to complete its octet, achieving a stable, noble gas electron configuration.

Identify the Charge of the Other Element

For each given element, determine its typical ionic charge: (a) Barium typically forms a cation with a charge of \(2+\), \(\text{Ba}^{2+}\). (b) Lithium forms a cation with a charge of \(1+\), \(\text{Li}^{+}\). (c) Aluminum forms a cation with a charge of \(3+\), \(\text{Al}^{3+}\).

Write the Chemical Formula for Each Compound

For each combination, balance the charges to determine the simplest compound formula:(a) Barium selenide: Combine \(\text{Ba}^{2+}\) and \(\text{Se}^{2-}\) to form \(\text{BaSe}\) because the charges are equal and opposite.(b) Lithium selenide: Two \(\text{Li}^{+}\) ions are needed to balance one \(\text{Se}^{2-}\) ion, giving \(\text{Li}_2 ext{Se}\).(c) Aluminum selenide: Two \(\text{Al}^{3+}\) ions need to balance three \(\text{Se}^{2-}\) ions, resulting in \(\text{Al}_2 ext{Se}_3\).

Key concepts

Ionic Compounds

Ionic compounds are fascinating entities formed when atoms transfer electrons among each other. This transfer is driven by the need to achieve a stable electron configuration, often resembling that of the nearest noble gas. The atoms involved in this exchange are typically a metal and a non-metal, creating what are known as cations and anions, respectively. The differing charges of these ions, with cations being positively charged and anions being negatively charged, lead to a strong electrostatic attraction that holds the ions together. This is the essence of ionic bonding.

• Properties: Ionic compounds usually have high melting and boiling points due to their strong ionic bonds. They tend to form crystalline structures, which are often brittle and can dissolve in water to conduct electricity.
• Formation: The process begins when one element, typically a metal, loses electrons to become a positive ion or cation. Meanwhile, the non-metal counterpart gains those electrons to become a negative ion or anion.

Understanding the basic construction of ionic compounds provides insight into their significant presence in everyday materials around us.

Anion and Cation Charges

The concept of an anion and a cation is fundamental to understanding chemical reactions and how substances combine to form compounds. An ion is nothing but an atom or molecule that has gained or lost one or more electrons, leading to a net positive or negative charge. In the context of ionic compounds:

• Cations: These are positively charged ions that have lost electrons. Metals, like barium, lithium, and aluminum, usually form cations. For instance, barium loses two electrons to become \({\text{Ba}^{2+}}\), a common cation charge.
• Anions: These are negatively charged ions that have gained electrons. Non-metals usually form anions. Selenium, when it gains two electrons, forms \({\text{Se}^{2-}}\), an example of a common anion charge.

The interaction between cations and anions, which we can think of as an attractive dance of positive and negative charges, is the driving factor behind the formation of stable chemical compounds.

Selenium Compounds

Selenium is an intriguing element that often forms compounds through its ability to gain two electrons, resulting in the \({\text{Se}^{2-}}\) ion. This property is crucial in forming stable compounds with various metals.The creation of selenium compounds involves combining selenium's anion with metal cations:

• Barium Selenide (BaSe): Formed by the combination of \({\text{Ba}^{2+}}\) and \({\text{Se}^{2-}}\). Here, the charges balance out, leading to a straightforward 1:1 ratio of cations to anions.
• Lithium Selenide (Li₂Se): This compound forms when two lithium ions, \({\text{Li}^{+}}\), balance the charge of a single selenium ion, resulting in the formula \({\text{Li}_2\text{Se}}\).
• Aluminum Selenide (Al₂Se₃): Complex in structure as two aluminum ions, \({\text{Al}^{3+}}\), must combine with three selenium ions to balance out the charges, leading to the formula \({\text{Al}_2\text{Se}_3}}\).

Selenium's ability to easily form compounds with metals makes it a versatile component in various chemical processes and applications.