Which molecular geometries are planar

Sign up to join this community. The best answers are voted up and rise to the top. Stack Overflow for Teams — Collaborate and share knowledge with a private group. Create a free Team What is Teams? Learn more. How can I tell whether or not a molecule is planar?

Ask Question. Asked 4 years, 11 months ago. Active 3 years, 8 months ago. Viewed 82k times. We take in account the geometric distribution of the terminal atoms around each central atom.

For the final description, we combine the separate description of each atom. In other words, we take long chain molecules and break it down into pieces. Each piece will form a particular shape.

Follow the example provided below:. Butane is C 4 H C-C-C-C is the simplified structural formula where the Hydrogens not shown are implied to have single bonds to Carbon. You can view a better structural formula of butane at en. Let's start with the leftmost side. We see that C has three single bonds to 2 Hydrogens and one single bond to Carbon. That means that we have 4 electron groups. By checking the geometry of molecules chart above, we have a tetrahedral shape.

Now, we move on to the next Carbon. This Carbon has 2 single bonds to 2 Carbons and 2 single bonds to 2 Hydrogens. Again, we have 4 electron groups which result in a tetrahedral. Continuing this trend, we have another tetrahedral with single bonds attached to Hydrogen and Carbon atoms. As for the rightmost Carbon, we also have a tetrahedral where Carbon binds with one Carbon and 3 Hydrogens.

Let me recap. We took a look at butane provided by the wonderful Wikipedia link. We, then, broke the molecule into parts. We did this by looking at a particular central atom. In this case, we have 4 central atoms, all Carbon. By breaking the molecule into 4 parts each part looks at 1 of the 4 Carbons , we determine how many electron groups there are and find out the shapes.

We aren't done, yet! We need to determine if there are any lone pairs because we only looked at bonds. Remember that electron groups include lone pairs! Butane doesn't have any lone pairs. Hence, we have 4 tetrahedrals. Now, what are we going to do with 4 tetrahedrals? Well, we want to optimize the bond angle of each central atom attached to each other. This is due to the electrons that are shared are more likely to repel each other.

With 4 tetrahedrals, the shape of the molecule looks like this: en. That means that if we look back at every individual tetrahedral, we match the central Carbon with the Carbon it's bonded to. Bond angles also contribute to the shape of a molecule. Bond angles are the angles between adjacent lines representing bonds.

The bond angle can help differentiate between linear, trigonal planar, tetraheral, trigonal-bipyramidal, and octahedral. The ideal bond angles are the angles that demonstrate the maximum angle where it would minimize repulsion, thus verifying the VSEPR theory. Essentially, bond angles is telling us that electrons don't like to be near each other. Electrons are negative. Two negatives don't attract. Let's create an analogy. Generally, a negative person is seen as bad or mean and you don't want to talk to a negative person.

One negative person is bad enough, but if you have two put together The two negative people will be mean towards each other and they won't like each other. So, they will be far away from each other. The geometries of molecules with lone pairs will differ from those without lone pairs, because the lone pair looks like empty space in a molecule.

Both classes of geometry are named after the shapes of the imaginary geometric figures mostly regular solid polygons that would be centered on the central atom and have an electron pair at each vertex. In the water molecule AX 2 E 2 , the central atom is O, and the Lewis electron dot formula predicts that there will be two pairs of nonbonding electrons.

The oxygen atom will therefore be tetrahedrally coordinated, meaning that it sits at the center of the tetrahedron. Two of the coordination positions are occupied by the shared electron-pairs that constitute the O—H bonds, and the other two by the non-bonding pairs. Therefore, although the oxygen atom is tetrahedrally coordinated, the bonding geometry shape of the H 2 O molecule is described as bent.

The effect of the lone pair on water : Although the oxygen atom is tetrahedrally coordinated, the bonding geometry shape of the H2O molecule is described as bent.

There is an important difference between bonding and non-bonding electron orbitals. Because a nonbonding orbital has no atomic nucleus at its far end to draw the electron cloud toward it, the charge in such an orbital will be concentrated closer to the central atom; as a consequence, nonbonding orbitals exert more repulsion on other orbitals than do bonding orbitals.

In H 2 O, the two nonbonding orbitals push the bonding orbitals closer together, making the H—O—H angle The electron-dot structure of NH 3 places one pair of nonbonding electrons in the valence shell of the nitrogen atom. This means that there are three bonded atoms and one lone pair for a coordination number of four around the nitrogen, the same as occurs in H 2 O. The Lewis dot structure for ammonia, NH3.

We can therefore predict that the three hydrogen atoms will lie at the corners of a tetrahedron centered on the nitrogen atom. The lone pair orbital will point toward the fourth corner of the tetrahedron, but since that position will be vacant, the NH 3 molecule itself cannot be tetrahedral; instead, it assumes a pyramidal shape, more specifically, that of a trigonal pyramid a pyramid with a triangular base.

The hydrogen atoms are all in the same plane, with the nitrogen outside of the plane. In 5-coordinated molecules containing lone pairs, these non-bonding orbitals which are closer to the central atom and thus more likely to be repelled by other orbitals will preferentially reside in the equatorial plane.

Example of a see-saw structure : Try to imagine this molecule teetering on each end, and you will have a visual representation of a see-saw. Hence the molecule has three electron pairs and is trigonal planar. Formaldehyde is the simplest member of a class of organic compounds called aldehydes.

These compounds have the structural component of the carbon double bond oxygen and at least one hydrogen atom and are always in the trigonal planar format geometry. Formaldehyde or methanal is a water soluble gas. Carbonate Ion:. In this example, CO 3 2- , the Lewis diagram shows carbon at the center with no lone electron pairs.