Question

Which is the smallest atom in Group \(7 \mathrm{~A}\) ?

Short answer

The smallest atom in Group 7A is Fluorine (F).

Step-by-step solution

Identify Group 7A elements

Group 7A of the periodic table is also known as the halogens. The elements in this group are: Fluorine (F), Chlorine (Cl), Bromine (Br), Iodine (I), and Astatine (At).

Understand Atomic Radius Trend

The atomic radius decreases across a period from left to right and increases down a group. This means that within a group, the smallest atom would be the one at the top.

Determine Smallest Atom in Group 7A

Since atomic radius increases down a group, the smallest atom in Group 7A (the halogens) is the one at the top, which is Fluorine (F).

Key concepts

Atomic Radius Trend

When we think of the atomic radius, we're considering the size of an atom. Atoms are not solid spheres but instead have a 'cloudy' area where electrons are likely to be found, and the atomic radius is the distance from the nucleus to the outer part of this cloud.
Across periods (which are rows on the periodic table), the atomic radius decreases from left to right. This happens because, as we move across a period, protons are added to the nucleus. More protons mean a larger positive charge, pulling electrons closer and shrinking the atomic size.
Down groups (which are columns), the atomic radius trend reverses - the size increases. New electron shells are added as we descend, making the atom bigger. In Group 7A, for example, starting from Fluorine (smallest) at the top to Astatine (largest) at the bottom, this is evident. More electron shells mean a greater distance from the nucleus, expanding the atomic radius.

Group 7A Elements

Group 7A of the periodic table is often referred to as the "halogens." The word "halogen" means "salt-former," which gives a hint about some of the chemical behaviors of these elements. This group includes the following five elements:

• Fluorine (F)
• Chlorine (Cl)
• Bromine (Br)
• Iodine (I)
• Astatine (At)

These elements are known for their high reactivity. They readily form compounds with metals to create salts. Fluorine and chlorine are gases at room temperature, bromine is a liquid, while iodine and astatine are solids.
What is particularly interesting about halogens is their unique ability to gain an electron; this makes them very reactive, especially with alkali metals and alkaline earth metals, forming ionic compounds. Their reactivity decreases down the group, meaning fluorine is the most reactive and astatine is the least.

Halogens

Halogens belong to Group 7A and stand out due to their properties and uses. These elements are all nonmetals and have seven electrons in their outer shell, just one short of a full octet. This configuration makes them eager to accept one electron to achieve a stable electron configuration.
The distinctive properties of halogens are often showcased in their readiness to form diatomic molecules (e.g., \( F_2 \), \( Cl_2 \)), where two atoms of the same element bond together.

• They are also known to have distinct colors and odors, such as the greenish gas chlorine and the purple sublimed iodine.
• Many halogens act as disinfectants, for example, chlorine and iodine kill bacteria and other pathogens effectively.

On the periodic table, halogens are located next to the noble gases, which are known for their lack of reactivity. However, halogens are the exact opposite, often aggressively forming compounds. This makes them crucial for a wide array of industrial and disinfectant applications.