Lesson 4: Physical Properties

• as more carbons are added to the hydrocarbon chain, the melting and boiling points increase
• hydrocarbons with a 1-4 carbon chain are gases at room temperature since all the boiling points are negative
• hydrocarbons with 5-16 carbons in the chain are liquid at room temperature
• hydrocarbons are nonpolar, which means they cannot dissolve in water
• the longer the chain is, the more dense it is since there are more London Dispersion forces between elements and more surface area
• ion-ion force: the attraction between formally charged ions, the strongest intermolecular force
• ion-dipole force: when ions interact a dipole of a polar molecule
• dipole-dipole force: when two polar molecules are attracted to each other based on their charges (e.g. H+ from an HCl molecule is attracted to a Cl- molecule from another HCl molecule)
• hydrogen bonds: when hydrogen is attracted to a highly electronegative atom (N, O, F) and the electronegative atom is bonded to a hydrogen
• London dispersion forces: nonpolar molecules are temporarily charged and the temporary dipoles are attracted to each other temporarily
• momentary dipole: when a molecule is temporarily charged, one side is partially positive and one side is partially negative
• if the intermolecular forces are stronger, atoms are more tightly packed so more energy is needed to change its state
• nonpolar molecules can change state even with very slight energy input, since London Dispersion forces are weak
• hydrocarbons with 17 or more carbons in its chain are solids at room temperature