If I am placing intermolecular Forces in order by boiling point. weakest to strongest
C3H8
CH4
LiF
HBr
I'm not sure about the last two, is this in right order?
I would rank them as CH4, C3H8, HBr, LiF.
http://en.wikipedia.org/wiki/Intermolecular_force
To order the substances by boiling point from weakest to strongest intermolecular forces, you need to consider the types of intermolecular forces present in each compound. The strength of intermolecular forces generally increases with factors such as polarity, molecular size, and the presence of hydrogen bonding.
Let's analyze each compound and its intermolecular forces:
1. C3H8 (propane): Propane is a nonpolar molecule, consisting of carbon and hydrogen atoms. The only intermolecular force present is London dispersion forces, which are temporary attractions between instantaneous dipoles. These forces increase with increasing molecular size. Therefore, propane has the weakest intermolecular forces.
2. CH4 (methane): Methane is also a nonpolar molecule, made up of carbon and hydrogen atoms. Similar to propane, the only intermolecular force in methane is London dispersion forces. Methane is smaller than propane, so its dispersion forces are slightly weaker. Thus, methane has slightly stronger intermolecular forces than propane.
3. LiF (lithium fluoride): Lithium fluoride is an ionic compound composed of lithium cations (Li+) and fluoride anions (F-). Ionic compounds have strong electrostatic attraction between oppositely charged ions. This attraction, known as ionic bonding, is the strongest type of intermolecular force. Therefore, LiF has stronger intermolecular forces compared to propane and methane.
4. HBr (hydrogen bromide): Hydrogen bromide is a polar molecule with a partial positive charge on hydrogen (H) and a partial negative charge on bromine (Br). The intermolecular force present in HBr is dipole-dipole interaction. Although dipole-dipole forces are weaker than ionic bonding, they are stronger than London dispersion forces. So, HBr has stronger intermolecular forces compared to LiF.
Therefore, the correct order from weakest to strongest intermolecular forces is:
C3H8 < CH4 < HBr < LiF