Methane, bond angles structure

The structural features of methane ethane and propane are summarrzed rn Ergure 2 7 All of the carbon atoms have four bonds all of the bonds are srngle bonds and the bond angles are close to tetrahedral In the next sectron we 11 see how to adapt the valence bond model to accommodate the observed structures... 

FIGURE 2 7 Structures of methane ethane and propane showing bond distances and bond angles... 

Active Figure 1.11 The structure of methane, showing its 109.5° bond angles. Sign in at www.thomsonedu.com to see a simulation based on this figure and to take a short quiz. 

More subtle change can occur to a molecule s structure following photo-excitation. For example, the bond angle in methanal (formaldehyde) increases, so the molecule is flat in the ground state but bent by 30° in the first excited state see Figure 9.14. 

A fourth solvent structural effect refers to the average properties of solvent molecules near the solute. These solvent molecules may have different bond lengths, bond angles, dipole moments, and polarizabilities than do bulk solvent molecules. For example, Wahlqvist [132] found a decrease in the magnitude of the dipole moment of water molecules near a hydrophobic wall from 2.8 D (in their model) to 2.55 D, and van Belle et al. [29] found a drop from 2.8 D to 2.6 D for first-hydration-shell water molecules around a methane molecule. 

Like ammonia, the structure is similar to the tetrahedral structure of methane. The two lone pairs repel each other in order to be as far apart as possible. The squeezing of the hydrogens in water is even greater than that in ammonia. The H-O-H bond angle in water is 104.5°. 

Fig. 6J (a) The molecular structure of methane. (b) The molecular structure of ammonia showing (he reduction of bond angles, (c) The molecular structure of water showing the greater reduction of the bond angle by two lone pairs. 

A possible justification for frontside attack in electrophilic substitution is that ab initio molecular orbital calculations for the CH5+ cation, the species that would be formed if H+ attacked methane, indicate that the most stable structure would not be a trigonal bipyramid, in which carbon uses a p orbital to bond to two protons, but would be a relatively unsymmetrical structure that has a smallest H—C—H bond angle of about 37° (Figure 4.10).85 For further discussion of SB2 substitution on carbon, see Section 10.3.86... 

In this structure, there are three sigma bonds and one pair of nonbonding electrons. Four hybrid orbitals are required, implying sp3 hybridization and tetrahedral geometry around the nitrogen atom, with bond angles of about 109.5°. The resulting structure is much like that of methane, except that one of the sp3 hybrid orbitals is occupied by a lone pair of electrons. 

Methane has a tetrahedral structure with each C-H bond 109 pm and all the bond angles 109.5°. To simplify tilings, we shall draw a molecule of methane enclosed in a cube. It is possible to do this since the opposite corners of a cube describe a perfect tetrahedron. The carbon atom is at the centre of the cube and the four hydrogen atoms are at four of the corners. 

Structures for the two simplest acyclic alkanes were given in Chapter 1. Methane, CH4, has a single carbon atom, and ethane, CH3CH3, has two. All C atoms in an alkane are surrounded by four groups, making them sp hybridized and tetrahedral, and all bond angles are 109.5°. 

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