Structures with Four Regions of High Electron Its geometry will be called bent if it is bonded to two atoms and also has an unshared pair of electrons.Ĭ. The molecule is bent.Ī central atom surrounded by three clouds of high electron density will have trigonal planar geometry if it is bonded to three atoms. In the molecule, the oxygen-sulfur-oxygen atoms make a 120° angle. In sulfur dioxide, there are three electron clouds around the sulfur. The whole molecule is planar, and its shape resembles two triangles joined point to point. The ethylene molecule has trigonal planar geometry around each of its carbon atoms. A formaldehyde molecule is trigonal planar because it has an atom at the end of each electron cloud. Note that the angles are not exactly 120° but are remarkably close to that predicted value.Īlthough the electron clouds of these molecules give a trigonal planar shape around each carbon atom, one describes the geometry of a molecule only on the basis of the relationships between its atoms. If you experiment with a marshmallow as the central atom and three toothpicks as electron clouds, you can prove to yourself that the toothpicks are farthest apart when using a trigonal planar structure. The central atom will be in the center of the triangle, and the ends of the electron clouds at the corners of the triangle. For these clouds to be as far as possible from one another, they will form a plane containing the central atom and will emanate from the central atom at angles of 120° to each other. The sulfur atom in sulfur dioxide and the carbon atom in ethylene and formaldehyde is surrounded by three clouds of high electron density. In formaldehyde and ethylene, each carbon atom has two single bonds to hydrogen, a double bond to another atom, and no unshared pair. In sulfur dioxide, the sulfur atom is bonded to two oxygen atoms and has one unshared pair of electrons. In these molecules, each central atom has three electron clouds emanating from it. Structures with Three Regions of High Electron Density around the Central Atom Figure 7.6 shows the linear nature of these molecules.įIGURE 7.6 Linear molecules: (a) carbon dioxide, CO 2 (b) hydrogen cyanide, HCN and (c) acetylene, C 2H 2.ī. The VSEPR theory says, then, that the geometry around an atom that has only two bonds and no unshared electrons is a straight line.

For these two clouds to be as far away from each other as possible, they must be on opposite sides of the central atom, forming a Only two electron clouds emerge from that central atom. Notice that, in the Lewis structure of these molecules, the central atom(s) bonds with only two other atoms and has no unshared electrons. Some three-atom molecules also have straight-line geometry. If a molecule contains only two atoms, those two atoms are in a straight line and thus form a linear molecule. The VSEPR model states that the various regions containingĮlectrons or electron clouds around an atom spread out so that each region is We have already learned that like charges Each set of electrons, whether unshared or in a bond, createsĪ negatively charged region of space. May be involved in the formation of single, double, or triple bonds, or they Know that an atom has an outer shell of valence electrons. The VSEPR model can be explained in the following way. (VSEPR) model to predict the geometry of these and other covalently bonded In this section, we use the valence-shell electron-pair repulsion Molecules and ions containing various combinations of single, double, and tripleīonds. Unit of the covalent bond, and Lewis structures were drawn for several small In the previous section a shared pair of electrons was presented as the fundamental

So2 molecular geometry and bod angle