Little is known of the chemistry of astatine, the last member of Group 7A. Describe the physical characteristics that you would expect this halogen to have. Predict the products of the reaction between sodium astatide (NaAt) and sulfuric acid. (Hint: Sulfuric acid is an oxidizing agent.)

The Group 7A elements, also known as halogens, are a fascinating family in the periodic table comprising fluorine (F), chlorine (Cl), bromine (Br), iodine (I), and astatine (At). All halogens are non-metals with seven electrons in their outermost shell, which is the key to their high reactivity. They readily form compounds with metals and with each other, creating a vast array of salts and interhalogen compounds. As one moves down the group from fluorine to astatine, there is a notable trend of increasing atomic radius, atomic mass, melting point, and boiling point. This trend is due to the addition of electron shells as the atomic number increases.

Despite their shared group characteristics, halogens can vary widely. For instance, at room temperature, fluorine and chlorine are gases, bromine is a liquid, and iodine is a solid. Astatine, the least understood of the group due to its rarity and radioactivity, is also presumed to be a solid at room temperature. Each halogen has a distinct color as well, often becoming darker from fluorine to iodine.

The physical characteristics of the halogens are deeply intertwined with their position in the periodic table. These elements are known to be diatomic, meaning that they form molecules consisting of two atoms (e.g., F2, Cl2). Starting with the lightest halogen, fluorine is a pale yellow gas, while chlorine is a greenish-yellow gas. Bromine stands out as the only liquid halogen with a deep red-brown color, and iodine, a solid, exhibits a lustrous purple-black appearance. Astatine, the heaviest and rarest, would likely appear as a metallic-looking solid based on trend predictions.

The halogens also have increasing densities and atomic volumes as you move down the group. Fluorine has the lowest density and atomic volume, whereas astatine is expected to have the highest among the naturally occurring halogens. These trends are due to the increase in atomic weight and the addition of electron shells.

Halogens are very reactive due to their desire to gain an electron to achieve a stable octet configuration. They react with metals to form ionic salts, such as sodium chloride (NaCl), and they can also engage in reactions with non-metals to form covalent compounds. Fluorine is the most reactive of the halogens, capable of attacking glass and reacting with most elements from around the periodic table.

When it comes to chemical reactions with compounds, halogens can act as oxidizing agents. For example, chlorine can oxidize bromide ions to bromine. In the reaction of sodium astatide (NaAt) with sulfuric acid (H2SO4), the sulfuric acid acts as an oxidizing agent and we expect to form sodium hydrogen sulfate (NaHSO4) as a salt, and hydrogen astatide (HAt), following the pattern observed for other halogens. The chemical reactions of halogens are not only significant in inorganic chemistry but also play crucial roles in organic chemistry, with the addition of halogen atoms often significantly altering the behavior of hydrocarbons.