Molecules have shapes. There is wealth of experimental proof to the effect—from your physical nature to their chemical reactivity. Tiny molecules—molecules through a single central atom—have forms that can be easily predicted.

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The straightforward idea in molecular forms is dubbed valence covering electron pair repulsion (VSEPR)The general concept that estimates the shape of a straightforward molecule.. It basically claims that electron pairs, being created of negatively charged particles, repel each various other to acquire as far away native each other as possible. VSEPR provides a difference between electron group geometry, i m sorry expresses exactly how electron groups (bonds and also nonbonding electron pairs) space arranged, and molecular geometry, which expresses how the atoms in a molecule are arranged. However, the two geometries room related.

There space two species of electron groupsA covalent shortcut of any form or a lone electron pair.: any type of bond—single, double, or triple—and lone electron pairs. When applying VSEPR to simple molecules, the very first thing to execute is to count the variety of electron groups about the central atom. Remember that a multiple shortcut counts as only one electron group.

Any molecule with just two atoms is linear. A molecule whose central atom contains only two electron teams orients those two groups as much apart indigenous each other as possible—180° apart. Once the 2 electron teams are 180° apart, the atoms attached come those electron groups are additionally 180° apart, so the in its entirety molecular form is linear. Examples include BeH2 and CO2:


A molecule with 3 electron groups orients the three teams as far apart as possible. They take on the location of an it is intended triangle—120° apart and in a plane. The form of such molecules is trigonal planar. An example is BF3:


Some substances have a trigonal planar electron team distribution yet have atom bonded to only two that the 3 electron groups. An instance is GeF2:


From one electron team geometry perspective, GeF2 has a trigonal planar shape, yet its genuine shape is dictated by the location of the atoms. This shape is referred to as bent or angular.

A molecule with 4 electron groups about the central atom orients the 4 groups in the direction the a tetrahedron, as displayed in number 9.3 "Tetrahedral Geometry". If there are 4 atoms attached to these electron groups, climate the molecular shape is likewise tetrahedral. Methane (CH4) is an example.

Figure 9.3 Tetrahedral Geometry


Four electron teams orient us in the form of a tetrahedron.


This chart of CH4 illustrates the standard convention the displaying a three-dimensional molecule top top a two-dimensional surface. The directly lines space in the aircraft of the page, the hard wedged line is coming the end of the plane toward the reader, and the dashed wedged heat is going the end of the plane away from the reader.

NH3 is an example of a molecule whose main atom has 4 electron groups however only 3 of them are bonded to surrounding atoms.


Although the electron groups are oriented in the form of a tetrahedron, native a molecule geometry perspective, the shape of NH3 is trigonal pyramidal.

H2O is an instance of a molecule whose main atom has 4 electron groups however only two of them space bonded to neighboring atoms.

Although the electron groups are oriented in the form of a tetrahedron, the form of the molecule is bent or angular. A molecule with four electron groups around the main atom yet only one electron group bonded to another atom is linear due to the fact that there are only two atom in the molecule.

Double or triple bonds count together a single electron group. CH2O has actually the complying with Lewis electron period diagram.

The central C atom has actually three electron groups approximately it because the twin bond counts as one electron group. The 3 electron groups repel each various other to adopt a trigonal planar shape:

(The lone electron bag on the O atom room omitted for clarity.) The molecule will not it is in a perfect it is provided triangle due to the fact that the C–O double bond is various from the 2 C–H bonds, however both planar and triangular explain the suitable approximate form of this molecule.

Example 10

What is the approximate shape of each molecule?



The very first step is to attract the Lewis electron period diagram that the molecule.

For PCl3, the electron dot diagram is together follows:

The lone electron pairs on the Cl atoms room omitted for clarity. The ns atom has four electron teams with three of them external inspection to surrounding atoms, so the molecular shape is trigonal pyramidal.

The electron period diagram because that NOF is as follows:

The N atom has actually three electron teams on it, two of which room bonded to other atoms. The molecular form is bent.

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Test Yourself

What is the approximate molecular shape of CH2Cl2?



Table 9.3 "Summary of molecular Shapes" summarizes the shapes of molecules based upon their variety of electron groups and also surrounding atoms.

Table 9.3 an overview of molecular Shapes

number of Electron groups on central Atom variety of Surrounding atom Molecular form
any 1 linear
2 2 linear
3 3 trigonal planar
3 2 bent
4 4 tetrahedral
4 3 trigonal pyramidal
4 2 bent

Key Takeaway

The approximate form of a molecule can be predicted native the number of electron groups and the number of surrounding atoms.