Tetrahedral-shaped molecules

Find a flowering plant that interests you. Look at the root formation, leaf shapes and how they are attached to the stem, and the shape of the flower. Draw these different shapes. Find molecules that resemble these different shapes. Remember that group 3A elements form trigonal planar shaped molecules, group 4A elements form tetrahedral shaped molecules, group 5A elements form pyramid shaped molecules and group 6A elements form bent shaped molecules. Carbon chains have a zigzag shape and the DNA molecule is a double helix. You will see that these molecular shapes are duplicated in natural objects. See how many molecular shapes you can find in an ordinary flower. 

Methane is the simplest molecule with a tetrahedral shape, but many molecules contain atoms with tetrahedral geometry. Because tetrahedral geometry is so prevalent in chemistry, it is important to be able to visualize the shape of a tetrahedron. 

Tetrahedral shapes dominate the structures of biological molecules, as our Box describes. 

As it was mentioned in the formation of the NH3 molecule, compounds prefer configurations in which the electron pairs are as far apart as possible. Therefore oxygen undergoes sp3 hybridization resulting in a tetrahedral shape. 

If equal bond dipoles act in opposite directions in three-dimensional space, they counteract each other. A molecule with identical polar bonds that point in opposite directions is not polar. Figure 1.5 shows two examples, carbon dioxide and carbon tetrachloride. Carbon dioxide, CO2, has two polar C=0 bonds acting in opposite directions, so the molecule is non-polar. Carbon tetrachloride, CCI4, has four polar C—Cl bonds in a tetrahedral shape. You can prove mathematically that four identical dipoles, pointing toward the vertices of a tetrahedron, counteract each other exactly. (Note that this mathematical proof only applies if all four bonds are identical.) Therefore, carbon tetrachloride is also non-polar. 

This stiffness also has an influence on the shape of the dendrimers, when different core building units are employed. The biphenyl core 9 leads to the dumbbell shaped molecule whose most stable conformers show a twist between 20° and 60° around the central biphenyl unit. 2, based on the tetrahedral core 4, with a diabolo-like molecular shape which resembles the shape of the core very well. Due to the large number of benzene rings around the central methane unit, the branches are hindered in their rotation (Scheme 4), lowering the internal mobility of the molecule compared to 15. 

The shape of a molecule or ion is governed by the shape adopted by its constituent atoms. In PHj, for example, there are four electron pairs, but three of them are bonded pairs and one is a non-bonded pair. The four electron pairs adopt a tetrahedral shape but the three bonded pairs adopt a pyramidal shape. So the PHj molecule is described as pyramidal, not tetrahedral. As the base of this pyramidal structure is triangular rather than, say, square, the shape is more correctly referred to as trigonal pyramidal. 

The carbon two-valent state is converted to its four-valent state by unpairing the 2s electrons and promoting one of them to the third 2p orbital. The electrons from the four hydrogen atoms (red) make up four pairs of or bonding electrons, which repel each other to a position of minimum repulsion to give the tetrahedral shape for the methane molecule. 

In any molecule in which there are no nonbonding pairs around the central atom, the molecular shape is the same as the molecular geometry. Thus, to use the examples from Table 6.2, all three two-substituent molecules have both a linear geometry and a linear shape. Both BH3 and H2CO have a triangular planar shape, CH4 has a tetrahedral shape, PF5 a triangular bipyramidal shape, and SF6 a square bipyramidal shape. 

There are four substituents, which means that this molecule has the tetrahedral shape. 

Because valence electron octets are so common, particularly for second-row elements, the atoms in a great many molecules have shapes based on the tetrahedron. Methane, for example, has a tetrahedral shape, with H-C-H bond angles of 109.5°. In NH3, the nitrogen atom has a tetrahedral arrangement of its four charge clouds, but one corner of the tetrahedron is occupied by a lone pair, resulting in a trigonal pyramidal shape for the molecule. Similarly, H20 has two corners of the tetrahedron occupied by lone pairs and thus has a bent shape. 

The 1,2,5-dithiazepine 386, upon reaction with the adamantane 389, gave the symmetrically tetrasubstituted adamantane 391, whereas 386 and 388 upon treatment with 390 afforded the tetraphenylmethane 392 and its larger analogue 393 (Scheme 81). Similar procedures were adopted in synthesizing other tetrahedral-shaped nanoscale molecules <2003JOC4862>. 

Make your own clay. Find an area in your community where the soil is tightly packed and resembles clay. Dig out a ball of this soil. Add just enough water to make the soil plastic. Sculpt your clay into a molecular shape. It might be a bent water molecule or a tetrahedral-shaped methane molecule. Let your molecular model dry in sunlight. Paint your molecular model sculpture. 

Considering the tetrahedral shape of methane, construct a multiple-methane-molecule sculpture, or draw a picture of such an arrangement. Explain why the sculpture or drawing is abstract or nonobjective. How do the shapes in the sculpture or drawing evoke a mood or emotion How do the shapes show direction or movement ... 

In an atom, the hybridization of s and p orbitals to form sp orbitals provides electron probability areas where bonds can form to make a molecule more stable than if the bonding had occurred in the individual s and p orbitals. The sp orbitals have one large lobe and one small lobe and are aligned along x, y, and z coordinates so that four sp orbitals, called sp3 orbitals because they are made of one s and three p orbitals, result in a tetrahedral-shaped arrangement. When there are three sp orbitals, made of one s and two p orbitals, called sp orbitals, the molecular has a triangular-planar shape. If there is bonding in two sp orbitals, made of one s and one p orbital, a linear molecule results. 

In order for the electron pairs to be as far from each other as possible in a three-dimensional space, the molecule must have a tetrahedral shape, as shown in Figure 9.5. 

The idea of a tetrahedral shape is not confined to molecules having four atoms bonded to a central atom. An examination of the ammonia (NH3) molecule reveals another type. However, in this molecule the groups of valence electrons are in a tetrahedral con-... 

AB4 type) In molecules like CH4 CC14, SiH4, SiF4, NH4+, and BF4-, four bonding pairs of electrons are these in the valence shell of the central atoms A (one each by B). Geometrical arrangement that keeps the shared pairs of electrons as far as possible is the tetrahedral. These molecules are actually known to have tetrahedral shape. 

Drawing the Lewis structure of a molecule can help you determine the molecule s shape. In Figure 3.30, you can see the shape of the ammonia, NH3, molecule. The ammonia molecule has three bonding electron pairs and one lone pair on its central atom, all arranged in a nearly tetrahedral shape. Because there is one lone pair, the molecule s shape is pyramidal. The molecule methane, CH4, is shown in Figure 3.31. This molecule has four bonding pairs on its central atom and no lone pairs. 

Both the tetraarsene, AS4, and the methane, CH4, molecules have tetrahedral shapes (Figure 3-16) and Td symmetry. However, there is an important difference in their structures. In the As4 molecule, all... 

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