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Comparing covalent compounds

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  1. Comparing covalent compounds

  2. Intermolecular bonds • To determine relative melting points for ionic compounds, we looked at the strength of intramolecular bonds (bonds between atoms).

  3. Intermolecular bonds • To determine relative melting points for ionic compounds, we looked at the strength of intramolecular bonds (bonds between atoms). • To determine relative melting points for covalent compounds, we looked at the strength of intermolecular bonds (bonds between adjacent molecules).

  4. Intermolecular bonds • To determine relative melting points for ionic compounds, we looked at the strength of intramolecular bonds (bonds between atoms). • To determine relative melting points for covalent compounds, we looked at the strength of intermolecular bonds (bonds between adjacent molecules). • Single, double, and triple bonds tell us nothing about relative melting point.

  5. Melting point for covalent compounds • First, we must determine the polarity of the molecule. Polar molecules have higher melting points than nonpolar molecules.

  6. Melting point for covalent compounds • First, we must determine the polarity of the molecule. Polar molecules have higher melting points than nonpolar molecules. • If both compounds are polar, the one with the greater electronegativity difference will have a higher melting point.

  7. Melting point for covalent compounds • First, we must determine the polarity of the molecule. Polar molecules have higher melting points than nonpolar molecules. • If both compounds are polar, the one with the greater electronegativity difference will have a higher melting point. • If both compounds are nonpolar, the one with a greater number of overall electrons will have the higher melting point.

  8. Melting point visual aid

  9. Which substance has a higher melting point, CO or CO2?

  10. Which substance has a higher melting point, CO or CO2? • We need to determine the polarity of each substance. The difference in electronegativity will be the same for each compound, 0.89.

  11. Which substance has a higher melting point, CO or CO2? • We need to determine the polarity of each substance. The difference in electronegativity will be the same for each compound, 0.89. • Lewis structure for CO will not be symmetrical and is polar.

  12. Which substance has a higher melting point, CO or CO2? • We need to determine the polarity of each substance. The difference in electronegativity will be the same for each compound, 0.89. • Lewis structure for CO will not be symmetrical and is polar. • Lewis structure for CO2 O = C = O  nonpolar

  13. Which substance has a higher melting point, CO or CO2? • We need to determine the polarity of each substance. The difference in electronegativity will be the same for each compound, 0.89. • Lewis structure for CO will not be symmetrical and is polar. • Lewis structure for CO2 O = C = O  nonpolar • CO has the higher melting point

  14. Which substance is more likely to be a gas at room temperature, NH3 or PBr3?

  15. Which substance is more likely to be a gas at room temperature, NH3 or PBr3? • NH3 is polar according to the Lewis structure.

  16. Which substance is more likely to be a gas at room temperature, NH3 or PBr3? • NH3 is polar according to the Lewis structure. • PBr3 is also polar according to its Lewis structure.

  17. Which substance is more likely to be a gas at room temperature, NH3 or PBr3? • NH3 is polar according to the Lewis structure. • PBr3 is also polar according to its Lewis structure. • The substance with the smaller difference in electronegativity will will have weaker intermolecular bonds and is more likely to be a gas at room temperature.

  18. Which substance is more likely to be a gas at room temperature, NH3 or PBr3? • NH3 is polar according to the Lewis structure. • PBr3 is also polar according to its Lewis structure. • The substance with the smaller difference in electronegativity will will have weaker intermolecular bonds and is more likely to be a gas at room temperature. • PBr3

  19. Which substance has a higher boiling point, N2 or O2?

  20. Which substance has a higher boiling point, N2 or O2? • Both substances have an electronegativity difference of zero and are nonpolar.

  21. Which substance has a higher boiling point, N2 or O2? • Both substances have an electronegativity difference of zero and are nonpolar. • The substance with more electrons will have the higher boiling point.

  22. Which substance has a higher boiling point, N2 or O2? • Both substances have an electronegativity difference of zero and are nonpolar. • The substance with more electrons will have the higher boiling point. • N2 has 14 electrons, O2 has 16 electrons, oxygen has the higher boiling point.

  23. Naming binary covalent compounds • A binary covalent compound consists of exactly two nonmetals.

  24. Naming binary covalent compounds • A binary covalent compound consists of exactly two nonmetals. • The name of the first nonmetal is the name of the element with a latin prefix to represent the subscript (unless it’s 1).

  25. Naming binary covalent compounds • A binary covalent compound consists of exactly two nonmetals. • The name of the first nonmetal is the name of the element with a latin prefix to represent the subscript (unless it’s 1). • The name of the second nonmetal must end in -ide with a latin prefix to represent the subscript (even if it’s 1).

  26. Latin prefixes • mono-

  27. Latin prefixes • mono- • di-

  28. Latin prefixes • mono- • di- • tri-

  29. Latin prefixes • mono- • di- • tri- • tetra-

  30. Latin prefixes • mono- • di- • tri- • tetra- • penta-

  31. Latin prefixes • mono- • di- • tri- • tetra- • penta- • hexa-

  32. Latin prefixes • mono- • di- • tri- • tetra- • penta- • hexa- • hepta-

  33. Latin prefixes • mono- • di- • tri- • tetra- • penta- • hexa- • hepta- • octa-

  34. Examples • CCl4 =

  35. Examples • CCl4 = carbon tetrachloride • P2O5 =

  36. Examples • CCl4 = carbon tetrachloride • P2O5 = diphosphorus pentoxide • CO =

  37. Examples • CCl4 = carbon tetrachloride • P2O5 = diphosphorus pentoxide • CO = carbon monoxide