Which molecule has a tetrahedral geometry?

Which molecule has a tetrahedral geometry?

• A. Methane
• B. Ammonia
• C. Water
• D. Phosphorus pentachloride

Answer: (A)

The shape of a molecule is guided by how the electron pairs around a central atom arrange themselves to minimize repulsion. When there are four electron domains around the central atom and none are lone pairs, they spread out as far as possible in three dimensions, forming a regular tetrahedron with bond angles of about 109.5 degrees. Methane fits this exactly: the carbon atom is bonded to four hydrogen atoms and has no lone pairs, so the four C–H bonds occupy the corners of a tetrahedron. This gives methane its characteristic tetrahedral geometry. Ammonia has one lone pair on nitrogen, which changes the arrangement to a trigonal pyramidal shape rather than tetrahedral. Water has two lone pairs, producing a bent shape. Phosphorus pentachloride has five bonding pairs around phosphorus, giving a trigonal bipyramidal geometry, not tetrahedral.

The shape of a molecule is guided by how the electron pairs around a central atom arrange themselves to minimize repulsion. When there are four electron domains around the central atom and none are lone pairs, they spread out as far as possible in three dimensions, forming a regular tetrahedron with bond angles of about 109.5 degrees.

Methane fits this exactly: the carbon atom is bonded to four hydrogen atoms and has no lone pairs, so the four C–H bonds occupy the corners of a tetrahedron. This gives methane its characteristic tetrahedral geometry.

Ammonia has one lone pair on nitrogen, which changes the arrangement to a trigonal pyramidal shape rather than tetrahedral. Water has two lone pairs, producing a bent shape. Phosphorus pentachloride has five bonding pairs around phosphorus, giving a trigonal bipyramidal geometry, not tetrahedral.