Trigonal planar shape molecule

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. 

This molecule is of the AX3 type it has a trigonal planar electron-group geometry and a trigonal planar shape. 

The shape around this carbon atom is trigonal planar. The molecule lies flat in one plane around the central carbon atom, with the three bonded atoms spread out, as if to touch the corners of a triangle. 

The NF3 molecule has two extra electrons, compared to BF3, which would occupy an anti-bonding 7t-type 2a/ orbital if it had a trigonally planar shape. The C1F3 molecule with another two electrons would make use of the anti-bonding or-type 4a,7 orbital if the molecule were to be trigonally planar. It is to avoid use of anti-bonding orbitals that they adopt different symmetries. 

SOLUTION (a) According to the VSEPR model, BF3 is a trigonal planar AX3 molecule. This shape has a symmetry in which all three bond dipoles cancel. It is listed in Fig. 3.10 and classified there as nonpolar (see also 6). (b) According to the VSEPR model, the 03 molecule is angular, with one lone pair on the central O atom (37). Two positions around that central O atom are linked to O atoms, but the third is a lone pair, making it an AX2E molecule. The dipoles do not cancel as a result, the molecule is polar. This example shows that a homonuclear polyatomic molecule can be polar. 

The value of the dot and cross structure here is to help to ensure that all the electrons are accounted for before attempting to deduce the structure. The electron pair repulsion theory gives the result that the CC12 molecule has a trigonal planar shape. There are two C-Cl single bonds and also (formally)... 

Earlier, we looked at the BC13 molecule and observed that it adopted a trigonal planar shape. 

Figure 8.18 Electron pairs in a molecule are located as far apart as they can be, just as these balloons are arranged. Two pairs form a linear shape. Three pairs form a trigonal planar shape. Four pairs form a tetrahedral shape. 

The three electron pairs around boron minimize the repulsion between them when the molecule adopts the trigonal planar shape. The fluorine atoms are in the same plane, at the three corners of a triangle drawn around the central atom. The three angles between the B-F bonds are all 120°. 

All bonding groups trigonal planar shape (AY ). Boron trifluoride (BF3), another molecule in which the central atom is electron deficient, is an example. It has six electrons around the central B atom in three single bonds to F atoms. The four nuclei lie in a plane, and each F—B—F angle is 120° ... 

The use of the idea of hybridization also explains the observed shape of the methane molecule. The four sp hybridized carbon atoms can then overlap with the Is electrons of four hydrogen atoms (Figure 14.36) to form four o bonds arranged tetrahedrally around the central carbon atom. Atoms joined by single covalent bonds can usually rotate freely about the bond. The linear shape of BeF2 and the trigonal planar shape of BF3 can be understood similarly. 

Section 1 10 The shapes of molecules can often be predicted on the basis of valence shell electron pair repulsions A tetrahedral arrangement gives the max imum separation of four electron pairs (left) a trigonal planar arrange ment is best for three electron pairs (center) and a linear arrangement for two electron pairs (right)... 

Valence shell electron-pair repulsion (VSEPR) model (Section 1.10) Method for predicting the shape of a molecule based on the notion that electron pairs surrounding a central atom repel one another. Four electron pairs will arrange themselves in a tetrahedral geometry, three will assume a trigonal planar geometry, and two electron pairs will adopt a linear arrangement. 

The two extra electrons in the sulfite ion, S032, cause its shape to be different from the S03 molecule. The SO 32 ion is trigonal pyramidal with 4 regions of high electron density, whereas the S03 molecule is trigonal planar. 

The geometry of the BH3 molecule is trigonal planar. The net vectorial force applied on the boron atom by the three polar bonds is zero due to the symmetrical shape, so the molecule is nonpolsur. 

The shape of the BF3 molecule is trigonal planar but NH3 molecule is trigonal pyramidal. Explain the reason for this difference. 

Boron is in Group 3 and so has three electrons in the outer shell. The three Cl atoms contribute one electron each, giving a total of six electrons involved in bonding. So there are three B-Cl bonds and no non-bonding pairs on the boron atom. The shape of the boron trichloride molecule will be trigonal (or trigonal planar) with all four atoms in the same plane. 

Figure 6.8 A diagram showing the interaction of the 4a/ and 282" MOs of trigonally planar NF3 permitted by a distortion of the molecule, giving a shape of lower symmetry, i.e. trigonally pyramidal...

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