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

Which molecule has four single covalent bonds as shown in its dot and cross diagram?

1. Water, H₂O

2. Methane, CH₄

3. Ammonia, NH₃

4. Carbon Dioxide, CO₂

The correct answer is: Methane, CH₄

The molecule that has four single covalent bonds is methane, represented by the chemical formula CH₄. In the dot and cross diagram for methane, carbon is the central atom and forms four single covalent bonds with four hydrogen atoms. Each bond is formed by the sharing of one electron from carbon and one electron from each of the hydrogen atoms, resulting in a stable configuration. Methane is a classic example of a molecule that demonstrates the tetrahedral geometry resulting from these four single covalent bonds. This arrangement allows for a symmetric distribution of the hydrogen atoms around the carbon atom, which is essential for the stability and properties of methane. In contrast, water has two single covalent bonds; ammonia has three single covalent bonds; and carbon dioxide features two double bonds between carbon and each oxygen atom, not single bonds. These differences in bonding structures explain why methane is the only molecule among the choices with four single covalent bonds.