Carbon bond enthalpy terms

Ethyne, ethene and ethane contain 10. 12 and 14 valence electrons, respectively. They are isoelectronic with N2, 02 and F., respectively. Along both series of molecules the central link becomes progressively weaker and the bond lengths increase. The carbon-carbon bond length increases from 121 pm in ethyne to 133 pm in ethene and to 155 pm in ethane. The corresponding bond enthalpy terms are 837, 612 and 348 kJ mol Data for the diatomic molecules is contained in the text. Discuss these data in terms of the VSEPR and MO treatments of the molecules. 

Reference to Table 2 indicates the scale of increase expected for metal-ligand bond enthalpy terms as the ratio of ligand to metal decreases. Taking "(Os-CO) for Os(CO)4 units as 201 kJmol", as found for Os3(CO)i2, we estimate that a realistic value of (Os-CO) for Os(CO)3 units will be some 4% higher, i.e. 209 kJmor. Using these values, one can estimate values of the enthalpy of disruption of all the known osmium carbonyls Os.v(CO)j. into gaseous metal atoms and carbon monoxide molecules ... 

Table 10.2 compares some bond enthalpy terms for single bonds in carbon compounds and in silicon compounds. 

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