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

In a dot and cross diagram for ammonia, NH₃, how many hydrogen atoms are shown bonded to nitrogen?

1. One

2. Two

3. Three

4. Four

The correct answer is: Three

In a dot and cross diagram for ammonia (NH₃), nitrogen forms bonds with three hydrogen atoms. Each hydrogen atom is represented by a dot or cross in the diagram, showing the sharing of electrons. Nitrogen has five electrons in its outer shell and needs three more to achieve a stable octet configuration. Each hydrogen atom contributes one electron, forming a single covalent bond with nitrogen. Therefore, in total, there are three hydrogen atoms bonded to the nitrogen atom in ammonia. This structure effectively illustrates how nitrogen uses its available electrons to bond with three hydrogen atoms, resulting in a stable molecular structure for ammonia.