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

What type of structure does methane, CH₄, have as depicted in its dot and cross diagram?

1. Linear structure

2. Tetrahedral structure

3. Planar structure

4. Octahedral structure

The correct answer is: Tetrahedral structure

Methane (CH₄) has a tetrahedral structure due to its molecular geometry, which arises from the arrangement of electron pairs around the central carbon atom. In a dot and cross diagram, the four hydrogen atoms are positioned around the central carbon atom at angles of approximately 109.5 degrees. This arrangement minimizes the electron pair repulsion according to VSEPR (Valence Shell Electron Pair Repulsion) theory, leading to a stable geometry. In a tetrahedral structure, one can visualize the carbon atom at the center of a tetrahedron with the four hydrogen atoms occupying the corners. This three-dimensional arrangement is crucial for understanding methane's properties and reactivity, as it influences how the molecule interacts with other substances. Other structural options, such as linear, planar, or octahedral, do not accurately describe methane's arrangement. A linear structure would only accommodate two atoms in a straight line, which is not applicable in this case. A planar structure suggests all atoms lie in the same plane, which is also not true for CH₄. An octahedral structure involves six groups around a central atom, which exceeds the number of surrounding atoms in methane. Thus, the correct identification of methane's structure as tetrahedral illustrates its unique bonding and