Octahedral in Molecular Geometry: Shape & Structure

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  • 0:04 Molecular Geometry
  • 0:22 VSEPR Theory
  • 1:25 Octahedral Shape
  • 1:59 Bond Angles in…
  • 2:28 Examples of Octahedral…
  • 3:01 Lesson Summary
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Lesson Transcript
Instructor: Mia Primas

Mia has taught math and science and has a Master's Degree in Secondary Teaching.

In this lesson you will learn about the shape and structure of octahedral molecules. We will discuss the angles formed within the molecules, then we will look at a few examples.

Molecular Geometry

When we think of the structures of molecules in chemistry, we usually think of them as two-dimensional shapes. They're usually drawn this way for simplicity. However, many molecules have a three-dimensional structure. Molecular geometry is a type of geometry used to describe the shape of a molecule.

VSEPR Theory

When identifying the shape of a molecule, we need to first know the number of bonds and lone electron pairs with the molecule. The lone electron pairs are the electrons that surround the central atom but are not bonded to another atom. The total number of bonds and lone electron pairs determines the steric number of the molecule.

The presence of lone electron pairs affects the shape of the molecule. According to the Valence Shell Electron Pair Repulsion theory (VSEPR), electron pairs repel each other whether they are bonded or in lone pairs. This repulsion is due to the negative charge of the electrons. Like charges repel each other. VSEPR theory also states that the electrons and atoms of the molecule will arrange themselves to minimize the repulsion. The arrangement that takes place is what gives the molecule its geometric structure. Octahedral molecules have six atoms bonded to the central atom and no lone electron pairs, making the steric number equal to six.

Octahedral Shape

We know that an octagon is a polygon with eight sides and an octuplet is a group of eight. After all, the prefix 'octa-' means eight. So you may be wondering why a molecule with six bonds is called an octahedral. To answer this we have to look at the shape that is formed by the outer atoms of the molecule. Imagine that the outer atoms are all connected. We can see that the connected atoms form triangles on each side of the molecule. If we were to unfold this shape and see it in two-dimensions, it would appear as eight connected triangles.

Bond Angles in Octahedral Molecules

The atoms of octahedral molecules are arranged on two planes that intersect at the central atom. The two planes form a 90-degree angle. The axial plane consists of the central atom and two of the surrounding atoms. They have a linear arrangement, meaning that they form a straight line. The second plane is the equatorial plane, which consists of the central atom and four surrounding atoms. The four bonds are spaced evenly creating 90-degree bond angles.

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