<p>Oh, and LDF's are in single atom nonmetals, ex Kr, Ne, Ar</p>
<p>how can you tell if it's polar or nonpolar?</p>
<p>Now I'm confused.</p>
<p>Forces and bonds are different right? Bonds occur within a molecule like Carbon with its covalent bonds (diamond) and Forces occur outside the molecule, attracting other molecules like CH4 with another CH4 (a nonpolar molecule). Right?</p>
<p>And it's the molecule's polarity and nonpolarity that determines the type of forces it has to attract other forces or in Hydrogen "bonding"'s case the H+ of one molecule being attracted to the negative end (with an open electron to attract H+) of another molecule.</p>
<p>edit:</p>
<p>So:</p>
<p>(weak) Dipole Dipole - Polar molecules
(weakest) LDF - Nonpolar molecules
(strongest) Hydrogen - H+ end of molecule with negative end of another molecule (a really electronegative one))</p>
<p>Neoking77 - Polar molecules must
1) have individual dipoles (covalent bonds between different atoms)
Ex: Cl2 has no dipoles, HCl has a dipole, CCl4 has four dipoles
2) the individual dipoles must not cancel each other out
Ex: HCl has a net dipole. CCl4 does not have a net dipole because its tetrahedral, so 3 dimensionally, the individual C-Cl dipoles cancel out.</p>
<p>Specify - you're correct, forces and bonds are different. But sometimes they both matter. Ex: Diamond has a higher MP than Cl2. Why?
Answer: Diamond is network covalent. Cl2 is molecular. Melting diamond would required breaking covalent bonds. Melting Cl2 requires overcoming intermolecular forces (specifically LDF's). Covalent bonds are stronger than intermolecular forces.</p>
<p>I'm pretty sure EVERYTHING has LDF.</p>
<p>Your ranking is generally correct, but sometimes people miss the fact that LDF's get much, much stronger as a molecule gets bigger (more electrons=more polarizable). If a molecule is large enough, its LDF's will be stronger than the dipole-dipole attraction between polar molecules.</p>
<p>thanks a lot gfaith and specify</p>
<p>Yes afruff and gfaith, I remember something like that now, it really depends on the case I guess.</p>
<p>Can we make a list of the cases (like w/ which formulas) we are to use which gas constant R (8.31 v. .0821)? And don't ignore me this time!!! (You guys forgot about one of my questions several pages back, but don't worry, I forgive you.)</p>
<p>PART II</p>
<p>Do we use pen on the free response?</p>
<p>And are SFs carried throughout the calculation? Or adjusted at the end?</p>
<p>LDF's should never be quoted as a justification for properties in anything EXCEPT covalent compounds and single atom nonmetals.
Ex: NaCl has a higher MP than KI. Explain.
Answer: NaCl and KI are both ionic compounds. Attractive forces between ionic compounds depend on coulomb's law - size of charge, and radius of ions. Both compounds are +1/-1, but K+ and I- are larger than Na+ and Cl-. Therefore the attractive forces (lattice energy) in KI are lower.</p>
<p>Note: No mention of LDF's. Ionic compounds do not have temporarily induced dipoles - they have permanent charges!</p>
<p>8.31 is used whenever you are working in energy units (joules)
0.0821 is used whenever you are working in pressure units</p>
<p>^Thank you. :). I'm going to fail by the way.</p>
<p>Ok, question. I am doing the 2003 Free response. Q3 is kinetics. There is a table of concentrations and initial rates, but there are 3 reactants. Do both of the other 2 reactants need to be constant when you find the order of the third, or does only 1 need to be held constant? I can't figure out how to do it.</p>
<p>mentioning LDF won't hurt you though. I.E., H20 has LDF as well as H-bonds, while CO2 only has a dipole and LDF.</p>
<p>LDF is the same thing as Vaan Der Waals forces, right?</p>
<p>For kinetics questions in MC, do we just look for a "nice" half-life to determine that it is first order.</p>
<p>
[quote]
LDF is the same thing as Vaan Der Waals forces, right?
[/quote]
</p>
<p>Dipole Dipole and LDF are both Vaan Der Waals forces.</p>