Michigan Test for Teacher Certification (MTTC) Secondary Integrated Science Practice test

What is the primary reaction characteristic of elements in Group 7A?

1. They are very stable

2. They combine violently with alkali metals to form salts

3. They exist solely in gaseous form

4. They do not react with other elements

The correct answer is: They combine violently with alkali metals to form salts

Elements in Group 7A, also known as the halogens, are characterized primarily by their ability to combine readily with alkali metals to form salts, a process that can be quite vigorous. This is due to the high electronegativity of halogens, which allows them to attract electrons from alkali metals. When a halogen reacts with an alkali metal, the alkali metal donates its one valence electron, resulting in the formation of an ionic bond and the production of a salt, such as sodium chloride (NaCl) when sodium (an alkali metal) reacts with chlorine (a halogen). This reaction typically releases a significant amount of energy, which is why it can be described as violent. The other options do not accurately reflect the characteristics of Group 7A elements. While the halogens are reactive, they are not very stable on their own; they tend to exist as diatomic molecules (e.g., Cl2, F2) and require reactions with other substances to achieve stability in compounds. Halogens do not exist solely in gaseous form; while fluorine and chlorine are gases at room temperature, bromine is a liquid, and iodine is a solid. Finally, halogens are known for their