Video: Identifying the Nonmetal Element That Is a Gas at 25°C and 1 atm in a Set of Elements

Which of the following is a nonmetal that is a gas at 25°C and 1 atm? [A] Fluorine [B] Phosphorus [C] Iodine [D] Aluminum [E] Silicon


Video Transcript

Which of the following is a nonmetal that is a gas at 25 degrees C at one atmosphere? A) Fluorine, B) phosphorus, C) iodine, D) aluminum, E) silicon.

The question is primarily asking us to identify a nonmetallic substance from a list of substances that are in fact elements. Some properties of metals and nonmetals are listed here for reference. We can use the periodic table to locate an element. Conveniently, it’s organized in such a way that metals are placed on the left side and nonmetals on the right. The boundary line is indicated by the pink line that looks a little bit like a staircase.

If we use the periodic table like a map, we discover that fluorine, symbol F, phosphorus, symbol P, iodine, symbol I, and silicon, symbol Si, are all nonmetals. Aluminum, symbol Al, is a metal. Aluminum and silicon are right next to each other in the same row or period of the periodic table. They sit on opposite sides of the metal–nonmetal boundary.

Aluminum is clearly a metal. It has a very high boiling point and conducts electricity very well due to its strong metallic bonding, where delocalized electrons are found. The question is asking us to identify a nonmetal. So we can eliminate aluminum from our possible answers.

Fluorine, phosphorus, iodine, and silicon are all nonmetals. They are possible correct answers. Looking at the question in more detail, we’re being asked to identify a substance that is a gas at 25 degrees C and one atmosphere. 25 degrees C is about normal room temperature. And one atmosphere is normal atmospheric pressure at sea level.

In our list of possible correct answers, phosphorus, iodine, and silicon are all solids at room temperature and pressure. Phosphorus exists as a dangerous white form, which is also toxic, and a more stable red form. Several other forms of phosphorus exist as well. All of these forms are solids. These forms of the same elements are called allotropes.

Iodine is a halogen in group 17 of the periodic table. It exists as a greater black solid, and it produces a purple vapor once heated. Silicon is a brittle, shiny, gray solid. It conducts electricity under certain conditions. So it’s described as a semiconductor.

We’re looking for a gaseous substance, so phosphorus, iodine, and silicon are also incorrect answers. The only possible answer here is fluorine. Fluorine is at the top of group 17 or seven, known as the halogens, is a pale yellow gas at room temperature and pressure. It’s a diatomic element, and it does not exist in nature due to its extreme reactivity. Fluorine is the correct answer here.

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