International General Certificate of Secondary Education (IGCSE) Chemistry Practice Exam

What is the primary characteristic of noble gases that differentiates them from other elements?

1. High reactivity

2. Low melting points

3. Full outer electron shells

4. Ability to form compounds easily

The correct answer is: Full outer electron shells

Noble gases are characterized by having full outer electron shells, which is a key aspect that differentiates them from other elements. This complete electron configuration provides them with stability and a lack of tendency to react with other elements. As a result, noble gases are often found in nature as monoatomic gases and are known for their lack of reactivity compared to elements with incomplete outer shells, which seek to gain, lose, or share electrons to achieve a more stable configuration. This full outer shell means that noble gases do not readily form chemical bonds or compounds, distinguishing them from other groups of elements that are more reactive and eager to participate in chemical reactions to complete their valence electron arrangements. Other characteristics, such as low melting points or the ability to form compounds, do not define noble gases in the same fundamental way as their electronic configuration does. Thus, the unique stability of having a full outer shell is what fundamentally sets noble gases apart in the periodic table.