Ok, how do you determine exactly which types of intermolecular forces are prevalent in molecules, and do you always have to have at least a pair? Btw, I've got the different types and whatnot, I'm just looking for how to assign them. Thanks.
dawooget
Favorite Answer
Yes, you need at least two atoms for a molecule, and therefore intermolecular forces. Look at the differences in electronegativity between the atoms (you have a chart where F=4.0). I'm going from memory, but if the differences are >1.7 then it's an ionic bond, and <1.7 then it's covalent.
That may not be exactly what's in the book, but it's in the right direction.
Anonymous
When a molecular is polar, it does not automatically mean that the intermolecular forces are dipole-dipole. Take for example water. Water is a polar molecule with the oxygen atom in it having two lone pairs of electrons. However, water forms hydrogen bonds and not dipole-dipole forces. Other examples of molecules that produce hydrogen bonds are ammonia, ethanol (dissolved in water) and hydrogen fluoride Take note, hydrogen bonds only form when: 1) There is a hydrogen atom involved 2) Hydrogen must be bonded to a highly electronegative element which are nitrogen (N), fluorine(F) and oxygen(O). However, an example where dipole-dipole forces come into play is in hydrogen chloride molecule. Because the chlorine is highly electronegative, it draws electrons away from the hydrogen atom, making it slightly positive, while the chlorine atom becomes slightly negative. Hence, the molecule of hydrogen chloride is a dipole. Trichloromethane is another example of a dipole molecule. Dipole moment sounds to me like your professor was referring to the London's dispersion forces (also known as Van der Waal's forces), which are totally different from hydrogen bonds and dipole-dipole forces. When a molecule is non-polar, yes it does automatically mean that the force is London's dispersion forces. However, in a dipole molecule, dipole-dipole forces are NOT the only intermolecular bonds involved. Take for example hydrazine (N2H4). Not only hydrogen bonds are acting but also London's dispersion forces. Yes, when there is hydrogen, and this hydrogen is bonded to F, O or N, then there is a hydrogen bond formed. An ionic bond is an interATOMIC bond, i.e, it is the bond formed by the electrostatic attraction between a positive charged ion and a negatively charged ion. I have never heard about ion-dipole forces before. Time to go research about it. I hope the link below helps.