Dipole-Dipole+Forces

__​What are Dipole-Dipole Forces?__ **//1)First of all, we need to be familiar with the meaning of __ dipole __//** . __ Dipole __ ** ---A partial (not complete) separation of positive and negative charge within a neutral particle.
 * What is dipole?

e.g.) water(H2O) * - The electronegativity of H is lower than that of O, which allows O to attract the shared electrons more strongly, making the shared electrons closer to O -The O side is more negative than H side, but the eletronegativity difference is not big enough for O to steal the electron completely from H, so the charge separation is partial(O side contains negative charge which is less than 1, and H side contains positive charge which is less than 1) -This is a __**Dipole**__ -one end of the compound is relatively negative and the another end is relatively positive

__ Dipole-Dipole Forces __ ---The intermolecular forces between two molecules with permanent dipoles. -Since the molecule has permanent dipole, one end of the molecule is relatively negative and the other end is relatively positive. -The relatively negative end of one molecule will attract the relatively positive end of another molecule, causing the two molecules to be close with each other. -This kind of attraction between two molecules is called the Dipole-Dipole Forces. (Forces between two dipoles/ two __polar molecules--elements have different electronegativities and the structure of the molecule is asymetrical.__ )
 * 2)Then, we can get into Dipole-Dipole Forces. ** & [[image:http://t2.gstatic.com/images?q=tbn:XF7-PjMQrV09LM: width="87" height="114"]]

Remember: The Dipole-Dipole Forces only exist between molecules with permanent dipoles!

What are the differences between dipole-dipole forces and London Forces? //** (For __hydrogen bonds__, special type of dipole-dipole forces, they're much stronger than normal dipole-dipole forces.) || **Weak intermolecular forces** (caused by temporary dipole/ temporary arrangement of electrons within molecules/atoms, sometimes most of the electrons stay at top of the molecule, causing the top is more negative than the bottom, sometimes they stay at the bottom, causing the bottom is more negative.) || (For __hydrogen bonds__, the bonds only exist between atoms H and O, F and N.) || **Exist all the time** (is important between covalent bonds with no dipoles.) || (The same trend for the __hydrogen bonds.__) || **Bigger atomic number/ electron number, bigger London Forces** (more electrons cause more charges and more attractions between molecules having temporary dipoles) ||
 * // 3)Dipole-Dipole Forces vs. London Forces
 * || ** Dipole-Dipole Forces ** || ** London **** Forces ** ||
 * ** Strongness ** || ** Weak intermolecular forces **
 * ** When is exist ** || ** Only between permanent dipoles **
 * **Factors that effect the strongness** || **More polar the molecules are** (bigger differences between electronegativity of elements), **stronger the Dipole-Dipole Forces**

Which one has the higher melting temperature, the one with dipole-dipole forces or the one with only London Forces? //** -Intermolecular forces of molecules with permanent dipoles= Dipole-Dipole Forces+ London Forces -Intermolecular forces of molecules with nonpermanent dipoles= London Forces -molecules with __similar amount of electrons__, London Forces are similar, therefore, the intermolecular forces between molecules with permanent dipoles are stronger than those of molecules without permanent dipoles. -The melting temperature/ boiling temperature of substances with Dipole-Dipole Forces/permanent dipoles are higher than that of substances with only London Forces/ nonpermanent dipoles.(molecules must have similar amount of electrons)
 * // 4)The melting temperature/ boiling temperature of substances having Dipole-Dipole Forces

What are Hydrogen Bond? //** -Hydrogen bonds exist between H and O, N, F. e.g.) HF, H2O # -The electronegetivity difference between these elements is so big that the charge difference between the two ends of one molecule is very big (positive end is more positive, negative end is more negative). -The more charges, the more attractions, the attraction between two molecules with hydrogen bond is very strong (very strong Dipole-Dipole Forces) . -The melting/boiling temperature of molecules with hydrogen bonds are higher than those have normal dipole-dipole forces (no hydrogen bonds) since the intermolecular bonds (hydrogen bonds) are much stronger. -Compared with the molecules with only London Forces as intermolecular bonds, if the numbers of electrons are similar, then the molecules with hydrogen bonds have much higher melting/boiling temperature. -That is, the melting/boiling temperature relationship within molecules is: hydrogen bonds> normal dipole-dipole forces> only London Forces (under the condition that the molecules have similar numbers of electrons.)
 * // 5)Special Dipole-Dipole ForcesHydrogen Bond

References: &www.rationalresponders.com/forum/16869
 * commons.wikimedia.org/wiki/File
 * 1) warforscience.blogspot.com