Section3.4IntermolecularForces创新.PDFVIP

Section 3.4: Intermolecular Forces Mini Investigation: Relating Boiling Points to Intermolecular Forces, page 113 A. Answers may vary. Sample answer : The larger the molecule, the more electrons and protons there are attracting each other, the stronger the London dispersion forces, and thus the higher the boiling point. The size of an atom increases as you go from right to left across a period and as you go down a group. The hydrogen compounds in a group are identical except for a non- hydrogen atom. I hypothesize that the boiling points of hydrogen compounds in Groups 14 to 17 will increase as the non-hydrogen atom in the compound moves from right to left across a period, and will also increase as you go down a group. Electronegativity of atoms decreases as you go from right to left across a period and from top to bottom down a group, so the electronegativity differences of the bonds in the hydrogen compounds in Groups 14 to 17 and thus the polarity of the molecules will also decrease as the non-hydrogen atom in the molecule moves from right to left across a period and from top to bottom down a group. The more polar a substance is, the stronger the dipole–dipole force of attraction between its molecules. A more polar molecule will have a higher melting point. This supports my hypothesis that the boiling points of hydrogen compounds will increase from Group 14 to 17 and will increase as you go down a group. Hydrogen bonds will be found in molecules that have hydrogen and a highly electronegative atom such as nitrogen, oxygen, or fluorine. Since hydrogen bonds are the strongest intermolecular bonds, molecules with hydrogen bonds should have the highest boiling points. These will be the molecules at the top of Groups 15, 16, and 17. B. Table 3 Boiling Points of the Hydrogen Compounds of Elements in Groups 14 to 17 Number of electrons Group Hydrogen compound