Three of the following molecular models have a tetrahedral central atom, and one does not. Which is the odd one? (There may be a 'hidden' atom directly behind a visible atom in some cases.) (a)
(b)
(c)
(d)

Key Concepts

Tetrahedral Geometry

Tetrahedral geometry occurs when a central atom is bonded to four other atoms, forming a shape where the bonds are directed towards the corners of a tetrahedron. This arrangement minimizes electron pair repulsion according to VSEPR theory, resulting in bond angles of approximately 109.5 degrees. Understanding this geometry is crucial for identifying which molecular models exhibit a tetrahedral structure.

VSEPR Theory

Valence Shell Electron Pair Repulsion (VSEPR) theory is a model used to predict the geometry of individual molecules based on the repulsion between electron pairs in the valence shell of the central atom. According to this theory, the spatial arrangement of atoms is determined by the need to minimize repulsion between electron pairs, which helps in predicting molecular shapes, including tetrahedral configurations.

Coordination Number

The coordination number refers to the number of atoms, ions, or molecules that a central atom can bond with in a complex or molecule. In the context of tetrahedral geometry, a coordination number of four indicates that the central atom is bonded to four other atoms. Identifying the coordination number is essential for determining whether a molecular model fits the tetrahedral description or is the odd one out.