Which of the following contribute to the attractive forces between noble gases and other nonpolar molecules? A) Network covalent bonds, B) Dipole-dipole interactions, C) London dispersion forces, D) Hydrogen bonds, or E) Ionic bonds.
We want to determine the attractive forces that are present in noble gases and other nonpolar molecules. So let’s go through our answer choices to figure out which one would be the best fit. Our first answer choice is network covalent bonds, which, like the name suggest, is a network of covalently bonded atoms. Two common examples of network covalent bonding is graphite and diamond. In graphite, we have a network of covalently bonded carbons that are each bonded to three other carbons. And in diamond, we have also a network of covalently bonded carbons. But the carbons are each bonded to four other carbons. Noble gases don’t typically form bonds except under extreme conditions. So we wouldn’t expect a noble gas to form a network of covalent bonds. So answer choice A is not the correct answer.
Dipole-dipole interactions occur due to differences in electronegativity between atoms. Which cause one end of a molecule to become partially negatively charged and the other end to become partially positively charged. If we have many of these molecules, the negatively charged end of one molecule will be attracted to the positively charged end of another. By definition, dipole-dipole interactions have to occur between molecules that are polar. But we’re interested in the attractive forces between noble gases and nonpolar molecules. So answer choice B is not the correct answer.
London dispersion forces are due to the instantaneous movement of electrons in a molecule or an atom. Typically, we think of electrons as being evenly distributed around the nucleus, like in the diagram on the left. But the electrons can move around within a molecule or atom, which could cause one part of the molecule, near the nucleus, to become positively charged and the other part to become negatively charged. We call this unequal distribution of charge due to the instantaneous movement of electrons and instantaneous dipole. These instantaneous dipoles can cause attractions between molecules or atoms. Since London dispersion forces are simply due to the movement of electrons, they’re present in all molecules. So they would certainly be present in noble gases and other nonpolar molecules.
Hydrogen bonds are a special kind of attractive force that occurs between hydrogen and highly electronegative atoms like nitrogen, oxygen, or fluorine. The electronegativity difference between hydrogen and the atom that it’s bonded to cause the hydrogen to become partially positively charged and the other atom to become partially negatively charged. The partially positively charged hydrogen from one molecule is then attracted to the extremely negatively charged lone pair from another molecule. Since lone pairs have such a high density of negative charge, hydrogen bonds can be quite strong, especially compared to other intermolecular forces. Hydrogen bonds occur between hydrogen and other electronegative atoms. So we wouldn’t expect them to occur in noble gases or nonpolar molecules. So answer choice D is not the correct answer.
Our last answer choice is ionic bonds, which typically occur between a nonmetal and a metal. In an ionically bonded compound, like NaCl, the nonmetal is much more electronegative than the metal. Since the nonmetal is so much more electronegative that the metal, it effectively steals an electron from the metal, causing there to be positively and negatively charged ions. Ionic bonds do not describe the attractive forces between noble gases and other nonpolar molecules. As they’re not composed of nonmetals and metals which form ions. So answer choice E is not the correct answer.
So as we suspected, London dispersion forces, which are due to the movement of electrons, contribute to the attractive forces between noble gases and other nonpolar molecules. So answer choice C is the correct answer.