Question

The element actinium is unstable and radioactive. Use the periodic table to predict the formula for actinium chloride, given the formula of lanthanum chloride, \(\mathrm{LaCl}_{3}\).

Short answer

The formula for actinium chloride is \( \mathrm{AcCl}_3 \).

Step-by-step solution

Understand the Given Information

We are given the formula of lanthanum chloride as \( \mathrm{LaCl}_3 \). Lanthanum (\( \mathrm{La} \)) is in the same group as actinium (\( \mathrm{Ac} \)) on the periodic table.

Identify the Characteristics of Actinium

Actinium is located in the same group as lanthanum in the periodic table. Elements in the same group often show similar chemical properties and form similar compounds. Both actinium and lanthanum are part of the actinide and lanthanide series, respectively.

Analyze the Chemical Properties

Since lanthanum forms a +3 oxidation state to create \( \mathrm{LaCl}_3 \), actinium also forms a +3 oxidation state due to similar group properties. This implies actinium forms compounds with similar stoichiometry as lanthanum.

Construct the Formula for Actinium Chloride

Using the information that actinium will form a +3 oxidation state, the formula for actinium chloride will be \( \mathrm{AcCl}_3 \). Each actinium atom will bond with three chloride ions to balance the charges.

Key concepts

The Periodic Table

The periodic table is a tabular arrangement of chemical elements ordered by increasing atomic number. Each row in the table is known as a period, while each column is referred to as a group. Elements in the same group often share similar properties because they have the same number of electrons in their outermost shell, which influences their chemical behavior. For instance, actinium and lanthanum belong to the same group, indicating they exhibit comparable chemical properties.
The grouping of elements helps in predicting the types of chemical compounds an element can form. Understanding how elements are organized in the periodic table is crucial for predicting their behavior in chemical reactions and for determining possible molecular structures, such as actinium forming a compound similar to lanthanum chloride, indicated as \( \mathrm{AcCl}_3 \).
The periodic table is like a map for chemists that provides insights into the reactivity and interaction of elements. This makes it an invaluable tool for identifying and forecasting how different elements will combine and react with each other.

Lanthanum Chloride

Lanthanum chloride, denoted as \( \mathrm{LaCl}_3 \), is a compound formed by the reaction of lanthanum metal with chlorine gas. Lanthanum is a soft, malleable, and ductile metal belonging to the lanthanide series of the periodic table. It exhibits a +3 oxidation state, leading it to bond with three chlorine ions to generate lanthanum chloride.
In chemistry, lanthanum chloride is often used in tubes for arc lamps, phosphors, and water treatments. It is prized for its high refractive index and low dispersion properties when part of optical materials.

• It is typically a white, crystalline solid.
• Lanthanum chloride is water-soluble, which allows its use in various aqueous chemical reactions.
• Its production and handling require careful consideration of its reactivity and the potential for hazardous reactions.

Understanding lanthanum chloride's properties helps predict the formation and characteristics of similar compounds, such as actinium chloride.

Chemical Properties

Chemical properties describe how a substance behaves during a chemical change. These include its reactivity with other chemicals, changes in composition, and the types of chemical bonds it forms. Elements that are in the same group often show similar chemical properties.
Actinium, similar to lanthanum, is expected to display certain characteristics based on their group placement in the periodic table:
- Both elements are likely to form +3 oxidation states.
- They share similar stoichiometric formulas in their chloride compounds: \( \mathrm{LaCl}_3 \) and \( \mathrm{AcCl}_3 \).
Studying the chemical properties of elements enables chemists to write the balanced chemical equations describing their reactions with other elements or compounds. More broadly, each element's position influences whether it acts as a metal or non-metal or forms acids, bases, or salts when reacting with other substances.

Oxidation State

An oxidation state refers to the degree of oxidation of an element in a chemical compound. It indicates the number of electrons lost or gained by an atom to form a bond within a compound. In the context of actinium and lanthanum, both exhibit a +3 oxidation state.
This +3 oxidation state suggests that these metals tend to lose three electrons when forming bonds with other elements. Such consistent behavior among elements within the same group facilitates predictions regarding their compound formation.

• For instance, actinium will lose three electrons to form bonds with chlorine, resulting in the compound \( \mathrm{AcCl}_3 \).
• Similarly, lanthanum also forms \( \mathrm{LaCl}_3 \) using a similar process.
  Identifying oxidation states helps chemists understand an element’s potential reactivity and the types of compounds it can form. It provides a foundational understanding for forming ionic compounds and understanding electron transfer during chemical reactions.