Molecular Geometry

Molecular geometry or molecular structure is the three-dimensional arrangement of the atoms that constitute a molecule. It determines several properties of a substance including its reactivity, polarity, phase of matter, color, magnetism, and biological activity.

Types of molecular structure

There are six basic shape types for molecules

Linear: Atoms are connected in a straight line. The bond angles are set at 180°. A bond angle is very simply the geometric angle between two adjacent bonds. For example, carbon dioxide has a linear molecular shape.

Trigonal planar: Molecules with the trigonal planar shapeare somewhat triangular and in one plane (meaning a flat surface). Consequently, the bond angles are set at 120°. An example of this is

boron trifluoride.

Tetrahedral: This is when there are four bonds all on one central atom, with no extra unshared electron pairs. In accordance with the VSEPR (valence-shell electron pair repulsion theory), the bond angles between the electron bonds are 109.5°. An example of a tetrahedral molecule is methane (CH4).

Octahedral: means "eight surfaces." The bond angle is 90 degrees.

An example of an octahedral molecule is sulfur hexafluoride (SF6).

Pyramidal: Pyramidal-shaped molecules have pyramid-like shapes. Unlike the linear and trigonal planar shapes but similar to the tetrahedral orientation, pyramidal shapes requires three dimensions in order to fully separate the electrons. Here, there are only three pairs of bonded electrons, leaving one unshared pair. The bond angles are 107.3°. An example is NH3 (ammonia).

Bent: The final basic shape of a molecule is the non-linear shape, also known as bent or angular. One of the most unquestionably important molecules any chemist studies is water, or H2O. A water molecule has a non-linear shape because it has two pairs of bonded electrons and two unshared pairs. Like in the other arrangements, electrons must be spaced as far as possible. Therefore, the bond angles here are 104.5°.