Why does methane have a tetrahedral shape

Also, VSEPR theory suggests that the geometry at the carbon atom in the methane molecule is tetrahedral 2 , and there exists a large body of both theoretical and experimental evidence supporting this prediction. According to valence bond theory, to form a covalent bond forms when an unpaired electron in one atom overlaps with an unpaired electron in a different atom.

Now, consider the the electron configuration of the four valence electrons in carbon. There is a serious mismatch between the electron configuration of carbon 1 s 2 2 s 2 2 p 2 and the predicted structure of methane. The modern structure shows that there are only 2 unpaired electrons to share with hydrogens, instead of the 4 needed to create methane.

Also, the p x and p y orbitals are at 90 o to each other. They would form perpendicular bonds instead of the tetrahedral Lastly, there are two different orbitals, 2 s and 2 p , which would create different types of C-H bonds. As noted earlier, experimentally, the four carbon-hydrogen bonds in the methane molecule are identical. An answer to the problems posed above was offered in by Linus Pauling. He showed mathematically that an s orbital and three p orbitals on an atom can combine to form four equivalent hybrid atomic orbitals.

In order to explain this observation, valence bond theory relies on a concept called orbital hybridization. In this picture, the four valence orbitals of the carbon one 2 s and three 2 p orbitals combine mathematically remember: orbitals are described by equations to form four equivalent hybrid orbitals , which are named sp 3 orbitals because they are formed from mixing one s and three p orbitals.

In the new electron configuration, each of the four valence electrons on the carbon occupies a single sp 3 orbital creating four unpaired electrons. The shape of an sp 3 hybridized orbital is a combination of s and p atomic orbitals.

Each sp 3 -hybridized orbital bears an electron, and electrons repel each other. To minimize the repulsion between electrons, the four sp 3 -hybridized orbitals arrange themselves around the carbon nucleus so that they are as far away as possible from each other, resulting in the tetrahedral arrangement predicted by VSPER.

This orbital overlap is often described using the notation: sp 3 C -1 s H. The formation of sp 3 hybrid orbitals successfully explains the tetrahedral structure of methane and the equivalency of the the four C-H bonds. What remains is an explanation of why the sp 3 hybrid orbitals form. Review of Atomic Orbitals for Organic Chemistry. If the orbital configuration of carbon is 2s 2 2p 2 , then how can we use this information to figure out what the arrangement of the orbitals are in a simple organic molecule like methane CH 4?

It turns out that methane is tetrahedral, with 4 equal bond angles of This brings up two questions. First, how do we know that CH 4 is tetrahedral? And secondly, how do we reconcile this electronic configuration 2s 2 2p 2 with the fact that we have four equal C—H bonds? In our review of atomic orbitals , we saw that the orbital configuration of the valence electrons of carbon is 2s 2 2p 2 as shown below:.

That means that there are two electrons in the 2s orbital, and a single electron in two of the three 2p orbitals. But in order to be truly useful, we need to be able to relate the orbitals of carbon to the structure and bonding of actual organic compounds. The simplest organic compound is methane, CH 4. As it turns out, it can be shown that this proposal is wrong. Recall that each C—H bond has a small dipole due to the difference in electronegativity between C 2. We expect C to be partially negative and H to be partially positive.

However, the measured dipole moment of CH 4 is zero. Therefore this cannot be the correct structure. Alright, you say. This was in fact the majority opinion for the arrangement of bonds around carbon until about Extremely brilliant chemists such as Berzelius went to their graves having no reason to doubt that methane was anything but flat. This is possible if the arrangement of 4 groups around the central carbon is tetrahedral, but not if the molecule is square planar.

For example, the methane derivative bromochlorofluoromethane has four different groups around carbon and can be separated into two different isomers which rotate plane-polarized light in different directions. This observation rules out the square planar structure. If carbon was square planar, the molecule would be flat, and be superimposable on its own mirror image, and only one isomer would be possible.

The fluorine atoms are positioned at the vertices of an equilateral triangle. Methane is an organic compound that is the primary component of natural gas. Its structure consists of a central carbon atom with four single bonds to hydrogen atoms see Figure 6.

In order to maximize their distance from one another, the four groups of bonding electrons do not lie in the same plane.

Instead, each of the hydrogen atoms lies at the corners of a geometrical shape called a tetrahedron. The carbon atom is at the center of the tetrahedron.

Each face of a tetrahedron is an equilateral triangle. The molecular geometry of the methane molecule is tetrahedral see Figure 7. The H-C-H bond angles are When drawing a structural formula for a molecule such as methane, it is advantageous to be able to indicate the three-dimensional character of its shape. The structural formula below is called a perspective drawing. The dotted line bond is to be visualized as receding into the page, while the solid triangle bond is to be visualized as coming out of the page.

When we travel, we often take a lot more stuff than we need. Trying to fit it all in a suitcase can be a real challenge.

We may have to repack or just squeeze it all in. Atoms often have to rearrange where the electrons are in order to create a more stable structure. The molecular geometries of molecules change when the central atom has one or more lone pairs of electrons. The total number of electron pairs, both bonding pairs and lone pairs, leads to what is called the electron domain geometry. When one or more of the bonding pairs of electrons is replaced with a lone pair, the molecular geometry actual shape of the molecule is altered.

In keeping with the A and B symbols established in the previous section, we will use E to represent a lone pair on the central atom A. A subscript will be used when there is more than one lone pair. Lone pairs on the surrounding atoms B do not affect the geometry. The ammonia molecule contains three single bonds and one lone pair on the central nitrogen atom see Figure 8.

The domain geometry for a molecule with four electron pairs is tetrahedral, as was seen with CH 4. In the ammonia molecule, one of the electron pairs is a lone pair rather than a bonding pair. The molecular geometry of NH 3 is called trigonal pyramidal see Figure 9. Recall that the bond angle in the tetrahedral CH 4 molecule is Again, the replacement of one of the bonded electron pairs with a lone pair compresses the angle slightly.

A water molecule consists of two bonding pairs and two lone pairs see Figure As for methane and ammonia, the domain geometry for a molecule with four electron pairs is tetrahedral. In the water molecule, two of the electron pairs are lone pairs rather than bonding pairs. The molecular geometry of the water molecule is bent. The H-O-H bond angle is The Lewis structure for SF 4 contains four single bonds and a lone pair on the sulfur atom see Figure The sulfur atom has five electron groups around it, which corresponds to the trigonal bipyramidal domain geometry, as in PCl 5 see Figure