Sigma bond overlap

The two C atoms join with a sigma bond overlap of sp2 on the left-hand C with sp on the right-hand C. The three bonds between C and N consist of a sigma bond (sp on C with sp on N), and two pi bonds (2p on C with 2p on N). 

In the valence bond theory, sigma bonds overlap on a line drawn between the two nuclei, while pi bonds result from the overlap of atomic orbitals above and below a line connecting the two atomic nuclei. 

When two p orbitals overlap in a side-by-side configuration, they form a pi bond, shown in Figure 7.7. This bond is named after the Greek letter 7t. The electron clouds in pi bonds overlap less than those in sigma bonds, and they are correspondingly weaker. Pi bonds are often found in molecules with double or triple bonds. One example is ethene, commonly known as ethylene, a simple double-bonded molecule (Figure 7.8). The two vertical p orbitals form a pi bond. The two horizontal orbitals form a sigma bond. 

Carbon atoms (1) and (4) use sp3 hybrid orbitals to form four sigma bonds, three by overlap with the hydrogen Is orbitals and one by overlap with an sp2 orbital from the central carbon (2). The two carbon atoms involved in the double bond undergo sp2 hybridization. They form C-H bonds by overlapping with Is orbitals of the H atoms. The C=C double bond is formed similarly to that described in (a). 

The left-most C atom (in the structure drawn below) is sp3 hybridized, and the C-H bonds to that C atom are between the sp3 orbitals on C and the Is orbital on H. The other two C atoms are sp hybridized. The right-hand C-H bond is between the sp orbital on C and the Is orbital on H. The c a C triple bond is composed of one sigma bond formed by overlap of sp orbitals, one from each C atom, and two pi bonds, each formed by the overlap of two 2p orbitals, one from each C atom (that is a 2py—2py overlap and a 2pz—2pz overlap). 

It is again clear from these diagrams that the 01,5 and 04,6 skeletal sigma bonds are allowed to adopt opposite phases for favorable oi,5-7t2,3 and 04,6-7 2,3 overlap with the oppositely phased lobes of 7t2,3 (and similarly for the two complementary 7 2,3 01,5 and 7t23 —>04 6 interactions). In contrast, the corresponding interactions with a bridging 01,4 bond (if present) would be forbidden to benefit from such stabilization. 

Similarly, C — H sigma bonds in the C2H6 molecule are formed by the end to end overlap of sp3 hybrid orbitals of the carbon atoms with the Is orbitals of the hydrogen atoms. The C—Co bond is formed by the end to end overlap of the sp3 hybrid orbitals of the C atoms. So in the C2H6 molecule there are six C — H o bonds and one C—Co bond making seven o bonds in total. 

In ethylene, there are two types of bonds. Sigma (tr) bonds have the overlap of the orbitals on a line between the two atoms involved in the covalent bond. In ethylene, the C-H bonds and one of the C-C bonds are sigma bonds. Pi (ir) bonds have the overlap of orbitals above and below a line through the two nuclei of the atoms involved in the bond. A double bond is always composed of one sigma and one pi bond. A carbon-to-carbon triple bond results from the... 

From the previous discussions, we expect the anti geometry to be stabilized due to the larger overlap integral between the C—C sigma bond and the empty sp3 orbital. 

The various atomic charges and bond overlap populations of CH2 = NH are shown below and confirm our expectations based on consideration of sigma conjugative effects. However, an anomaly is noted in the case of the 4—31G calculation of the C—Hb and C—Hc overlap populations. Since the STO—3G optimization leads to a longer C—Hc bond, as predicted, the anomaly represents most likely a computational artifact. 

Sigma (a) bonds Sigma bonds have the orbital overlap on a line drawn between the two nuclei, simple cubic unit cell The simple cubic unit cell has particles located at the corners of a simple cube, single displacement (replacement) reactions Single displacement reactions are reactions in which atoms of an element replace the atoms of another element in a compound, solid A solid is a state of matter that has both a definite shape and a definite volume, solubility product constant (/ p) The solubility product constant is the equilibrium constant associated with sparingly soluble salts and is the product of the ionic concentrations, each one raised to the power of the coefficient in the balanced chemical equation, solute The solute is the component of the solution that is there in smallest amount, solution A solution is defined as a homogeneous mixture composed of solvent and one or more solutes. 

Sigma bonds form when s or p orbitals overlap in a head-on manner. Single bonds cire usually sigma bonds. Pi bonds cire usually double or triple bonds. Figure 5-9 depicts these situations. 

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