Question

Little is known about the properties of astatine, \(\mathrm{At}\), 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 \(\mathrm{Na}\) ?

Short answer

Astatine is predicted to be a solid nonmetal at room temperature and the chemical formula of the compound it forms with sodium is \(\mathrm{NaAt}\).

Step-by-step solution

Determine the state of astatine at room temperature

Astatine is a member of Group 17 on the periodic table, which means it is a halogen. Other elements in this group include fluorine, chlorine, bromine, and iodine. As we move down the group, elements generally change their states from gas to liquid to solid at room temperature. Fluorine and chlorine are gases, bromine is a liquid, and iodine is a solid at room temperature. Since astatine is right below iodine, we can predict astatine to be a solid at room temperature.

Predict if astatine is a metal, nonmetal, or metalloid

Astatine is located near the metal-nonmetal borderline in the periodic table. As we move across a period from left to right, elements become less metallic and more non-metallic. Elements in Group 17 (halogens) are generally nonmetals. Considering its placement in the periodic table and behavior of other halogens, we can predict astatine to be a nonmetal.

Determine the chemical formula of the compound astatine forms with sodium

When a halogen reacts with an alkali metal like sodium (Na), an ionic compound is formed with the metal cation and the halogen anion. Sodium will form a cation with a +1 charge (Na+) and astatine will form an anion with a -1 charge (At-). The chemical formula of the compound formed by these ions will be \(\mathrm{NaAt}\) as their charges are equal in magnitude but opposite in polarity, which ensures neutrality of the compound. In summary, astatine is predicted to be a solid nonmetal at room temperature, and the chemical formula of the compound astatine forms with sodium is \(\mathrm{NaAt}\).

Key concepts

Group 17 Elements

Group 17 elements of the periodic table are referred to as halogens—a term derived from the Greek words 'halos' meaning salt and 'gen' meaning to form. This group includes fluorine, chlorine, bromine, iodine, and the less commonly discussed astatine.

As we observe these elements from top to bottom, they display a trend in their physical states at room temperature. Fluorine and chlorine exist as gases, bromine is found in a liquid state, and iodine is a solid. When we look at astatine, predictably following these trends, we would consider it a solid.

This progression from gas to solid within the group is attributed to increasing molecular mass and stronger intermolecular forces as one moves down the group. Understanding this trend helps us make educated guesses about the physical properties of astatine even though it is not directly observable due to its rarity and radioactivity.

Halogens Characteristics

Halogens are known for their distinct characteristics, which set them apart from other elements on the periodic table. They are highly reactive, especially with alkali metals, due to their strong electronegativity and the desire to achieve a stable octet by gaining an electron.

These elements form anions with a -1 charge, which manifests in many of their common compounds, such as table salt (NaCl). Halogens also have the interesting property of displaying a full spectrum of physical states across the group at room temperature and collectively exhibit vibrant and varied colors. As for astatine, despite uncertainty due to its radioactivity, its categorization as a halogen leads us to anticipate it being a nonmetal and sharing similar reactive qualities with its group members.

Ionic Compound Formation

Ionic compounds are formed through the transfer of electrons from one atom to another, which leads to the creation of ions with opposite charges that attract each other. An exquisite dance between positively charged cations and negatively charged anions results in the formation of a compound with an overall neutral charge.

In a typical reaction between a metal, such as sodium (Na), and a halogen like astatine (At), sodium donates an electron to become a positive ion (Na+), while astatine gains an electron to become a negative ion (At-). The resulting compound, NaAt, is formed through this balance of charge, which stabilizes the structure.

Ionic compounds have high melting and boiling points, conduct electricity when dissolved in water, and often form crystalline structures, showcasing the fundamental rule of electrostatic attraction in chemical bonding.