Boiling points, trends

Bohr frequency condition, 13 Bohr radius, 23 boiling, 314 boiling point, 314 alkanes, 737 anomalous, 184 boiling point prediction, 180 boiling point trends, 183 boiling-point elevation, 332 Boltzmann, L., 276 Boltzmann formula, 276 bomb calorimeter, 224... 

Within anv one section of Table 4.2, boiling points trend with what physical property ... 

The melting and boiling point trends of the first members of the monocarboxylic and dicarboxylic acid series are illustrated in Figs. 36 and 37. From the graphs, it can be seen that most of the monocarboxylic acids are liquids at room temperature, but all the dicarboxylic acids are solids. Also, the boiling points of most monocarboxylic acids are below reflow temperatures of solders utilized in electronic assemblies but are above solder reflow temperatures for dicarboxylic... 

Recall that boiling point trends are related to intermolecular forces. We should begin by identifying the types and strengths of intermolecular forces at work. 

The physical characteristics of /i /f-amyl alcohol diverge from the standard trends for the other alcohols it has a lower boiling point, higher melting point, higher vapor pressure, and low surface tension. Most notably, organic molecules are highly soluble in /i /f-amyl alcohol. 

Most of the reactions with quinolines and degassed Raney nickels have been carried out at the atmospheric boiling point (above 230 C), a condition which is known to favor the formation of by-products. With quinoline and 4-methylquinoline (lepidine), however, the yields of the 2,2 -biquinolines were increased three to four times by heating in vacuo at 150° C, and it seems probable that other quinolines will behave similarly. Table II also shows that the yields of 2,2 -biquino-lines obtained under comparable conditions vary with the position of the methyl group in a fashion reminiscent of the trends observed with the pyridines (Table I). This similarity extends to the behavior of the two 2-methyl substituted quinolines studied, which undergo loss of the 2-methyl group to some extent and form traces of 2,2 -biquinolines. 

Problem 17.3 The following data for isomeric four-carbon alcohols show that there is a decrease in boiling point with increasing substitution of the OH-bearing carbon. How might you account for this trend ... 

Table 6-VI11 presents some properties of the elements we are considering. The first three, sodium, magnesium, and aluminum, are metallic. The melting points and boiling points are high and increase as we go from element to element. This trend reflects stronger and stronger bonding and it is paralleled by a decrease in the atomic volume.

What is the significance of the trends in the boiling points and melting points of the inert gases in terms of attractions among the atoms ... 

How do the trends in physical properties for the halogens compare with those for the inert gases Compare boiling points, melting points, and atomic volumes. 

Consider first the boiling points of HI, HBr, HQ, and HF. The last, hydrogen fluoride, is far out of line, boiling at 19.9°C instead of below —95°C as would be predicted by extrapolation from the other three. There is an even larger discordancy between the boiling point of HjO and the value we would predict from the trend suggested by HjTe, HjSe, and H2S. 

Write out the electron configuration of sodium, magnesium, and aluminum and find the ionization energies for all their valence electrons (Table 20-IV, p. 374). Account for the trend in the heats of vaporization and boiling points (Table 20-1) of these elements. Compare your discussion with that given in Section 17-1.3. 

Trends in the properties of AH of vaporization and boiling point for the second- and third-row elements are compared in Table 20-V. 

SOLUTION The data in Fig. 2.12 show that electronegativity differences decrease from 1 HC1 to HI, and so the dipole moments decrease as well. Therefore, dipole-dipole forces decrease, too, a trend suggesting that the boiling points should decrease from HQ to HI. This prediction conflicts with the data so we examine the London forces. The number of electrons in a molecule increases from HQ to HI, and so the strength of the London interaction increases, too. Therefore, the boiling points should increase from HCl to HI, in accord with the data. This analysis suggests that London forces dominate dipole-dipole interactions for these molecules. 

Self-Test 5.2A Account for the trend in boiling points of the noble gases, which increase from helium to xenon. 

Self-Test 15.5B Explain the trends in the melting points and boiling points of the halogens. 

Consider the plot of the normal boiling points of the hydrogen halides in Fig. 5.8. Account foi the trend revealed by the graph. 

The line structures of butane, methyl ethyl ether, and acetone follow. Explain the trend in boiling points butane (0 °C), methyl ethyl ether (8 °C), and acetone (56 °C). 

Periodic trends in the boiling points of binary hydrogen compounds. Notice that H2O L HF, and NH3 are exceptions to the trends. 

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