Problem 74 - Chemistry The Central Science In Si Units

Question

Little is known about the properties of astatine, At, because of its rarity and high radioactivity. Nevertheless, it is possible for us to make many predictions about its properties. (a) Do you expect the element to be a gas, liquid, or solid at room temperature? Explain. (b) Would you expect At to be a metal, nonmetal, or metalloid? Explain. (c) What is the chemical formula of the compound it forms with Na?

Step-by-Step Solution

Answer

(a) Solid. (b) Nonmetal. (c) NaAt.

Step 1: Determining the State of Matter

Astatine is located in Group 17 of the periodic table, which is also known as the halogens group. Elements in the halogens group tend to have increasing melting and boiling points down the group. For example, fluorine and chlorine are gases at room temperature, bromine is a liquid, and iodine is a solid. Astatine, being below iodine, is expected to be a solid at room temperature due to even higher melting and boiling points.

Step 2: Predicting the Classification as Metal, Nonmetal, or Metalloid

Astatine is categorized as a halogen along with fluorine, chlorine, bromine, and iodine, which are nonmetals. Given its position in the periodic table and its similarities to iodine, astatine is expected to be a nonmetal. Although it is sometimes considered on the metalloid borderline, its chemical properties align more with those of nonmetals.

Step 3: Determining the Chemical Formula of the Compound with Na

In halogens, the typical oxidation state is -1 when they form compounds with metals such as sodium (Na), which has an oxidation state of +1. Therefore, the compound formed between sodium and astatine will be similar to that of other sodium halides like NaCl or NaI. The chemical formula of the compound is NaAt.

Key Concepts

Halogens are a fascinating group in the Periodic Table

They are found in Group 17 of the periodic table and are made up of five elements: fluorine, chlorine, bromine, iodine, and astatine. This group is known for the distinct pattern in their properties as you move from top to bottom. As you go down the group, the elements have higher melting and boiling points. Fluorine and chlorine are gases at room temperature, bromine is a liquid, and iodine is a solid. This trend suggests that astatine, which is below iodine, would also be a solid at room temperature.

• Fluorine and chlorine - gases
• Bromine - liquid
• Iodine and astatine - solids

Astatine is unique because it is rare and highly radioactive. These traits make it difficult to study in depth. However, by understanding its place in the halogens group, scientists can make educated predictions about its physical and chemical properties.

The Periodic Table organizes chemical elements

The periodic table is a powerful tool for chemists. It arranges elements based on their atomic number and similar properties. Each column, called a group, shares similar chemical characteristics. Halogens are in Group 17, characterized by having seven valence electrons, which makes them highly reactive.

The location of astatine in the periodic table gives clues about its behavior and properties. Due to its similarities with other halogens, astatine is expected to be a nonmetal. Elements are typically classified as metals, nonmetals, or metalloids based on their physical and chemical attributes. While astatine falls near the borderline of nonmetals and metalloids, it is generally considered a nonmetal because its properties align more closely with the other halogens.

• Metals typically conduct electricity and heat, are malleable, and have high melting points.
• Nonmetals are usually poor conductors and have significant variation in phase.
• Metalloids have properties of both metals and nonmetals.

Understanding astatine's place helps predict its characteristics despite its rarity and radioactivity.

Chemical Compounds involve specific interactions between elements

In chemistry, compounds are formed when two or more elements chemically bond. Halogens, like astatine, tend to form compounds with metals by gaining an electron to achieve a stable electron configuration. This is because they usually have an oxidation state of -1 in compounds. Consider sodium (Na), a metal, which donates an electron to become \(\text{Na}^+\). When it reacts with a halogen like astatine, which becomes \(\text{At}^-\), they form a stable ionic compound. The resulting compound between sodium and astatine is NaAt.

This compound formation follows the pattern seen with other halogens, like sodium chloride (NaCl) and sodium iodide (NaI). The uniformity in the formation of these compounds makes it easier to predict how astatine will interact with metals, despite its elusive nature.

• Na + At → NaAt (sodium astatide)
• Similar reactions occur with Na and other halogens: Na + Cl → NaCl
• This shows a broad pattern within the halogens' chemistry.

This common behavior underscores the predictability of chemical reactions within the same group in the periodic table.