[CHEM 002] - Final Exam Guide - Ultimate 41 pages long Study Guide!

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Published on 29 Mar 2017
School
Georgetown University
Department
Chemistry
Course
CHEM-002
Professor
Georgetown
CHEM 002
FINAL EXAM
STUDY GUIDE
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Intermolecular Forces
Intermolecular & intra molecular forces are different!
The covalent bond keeps atoms in a molecule togetherthese are intramolecular. The
iteroleular fores that e’ll deal ith here are the iteratios etee oleules.
Ex HCl & HCl
The strength of the bond between the hydrogen and the chlorine is a very strong
itraoleular attratio, ut e’re goig to study the iteroleular attratio etee the H
and Cl on different molecules.
The intermolecular attractions keep the substances in their condensed phase. Strongest
attractions are in solids, weaker in liquids, weakest in gasses. THEY ARE RESPONSIBLE FOR THE
PHASE OF THE SUBSTANCE AT ROOM TEMPERATURE.
The higher the boiling point, the stronger the intermolecular forces.
Since HCl is gaseous at room temperature, we know its intermolecular attractions are not very
strong.
In covalent, metallic, and ionic bonds (diamond, beryllium, and lithium fluoride respectively),
the hole thig is oe oleule so you a’t talk about intermolecular attractions.
Intermolecular forces include
- Dispersion force (N2)
- Dipole-dipole force (HCl)
- Hydrogen bonding force (HF)
The boiling point of these is lower.
Eletros are alays i otio, ut e a’t tell here they arewe have to settle with
probability functions (the wave function).
A node in the wave function means the electron is moving very fast, so it cannot be observed in
that loatio. The higher the uer of odes, the higher the eergy. That’s ho e arrage
molecular orbitalsvby looking at the number of nodes. Electrons are completely in motion.
This motion of electrons means that you have partial chargesthe electrons are not uniformly
distributed, they can be more on one side of the atom of the other, so the atom has more +/-
charge on the sides.
The charge on part of an atom makes electrons on atoms close to it repel to make a + there
and a o the other side….. ad it otiues. These are alled dispersion interactions.
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This happens to all molecules so it is the most important type of intermolecular interaction!
It’s a deidig fator a lot of the tie uless there is hydroge odig, hih e’re goig to
get to later.
Size is the most important.
Shape is also importantthe one that has more of a hot dog shape has higher IMF.
Observations:
- Size correlates with IMFs.
o This is because it correlates with number of electrons and ability to form dipoles.
- Halogens have higher boiling points than their respective noble gases.
o They’re diatoi so they’re tie the size! Beause they’re diatoi
o And also a hot-dog shape, which is why Cl2, which has the same weight as
Krypton, has a much higher boiling point
Ex. n-Pentane and Neopentane have the same molecular formula (C5H12) but different shape.
- The spherical neopentane has a lower boiling point (282.7K) than the linear n-pentane
(309.4K).
- The spherial oleule a’t for as ay dipoles as the liear oleule.
There are also dipole-dipole forces in polar molecules. These forces are permanent but require
that the orientation is correct they have to match up the and the positive. So depending on
hether the orietatio is or is’t orret, they a e attratie or repulsie.
They can cancel each other and therefore not actually contribute to IMFs. Therefore, dispersion
is probably a better bet.
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Document Summary

The covalent bond keeps atoms in a molecule together these are intramolecular. The i(cid:374)ter(cid:373)ole(cid:272)ular for(cid:272)es that (cid:449)e"ll deal (cid:449)ith here are the i(cid:374)tera(cid:272)tio(cid:374)s (cid:271)et(cid:449)ee(cid:374) (cid:373)ole(cid:272)ules. The strength of the bond between the hydrogen and the chlorine is a very strong i(cid:374)tra(cid:373)ole(cid:272)ular attra(cid:272)tio(cid:374), (cid:271)ut (cid:449)e"re goi(cid:374)g to study the i(cid:374)ter(cid:373)ole(cid:272)ular attra(cid:272)tio(cid:374) (cid:271)et(cid:449)ee(cid:374) the h and cl on different molecules. The intermolecular attractions keep the substances in their condensed phase. Strongest attractions are in solids, weaker in liquids, weakest in gasses. The higher the boiling point, the stronger the intermolecular forces. Since hcl is gaseous at room temperature, we know its intermolecular attractions are not very strong. In covalent, metallic, and ionic bonds (diamond, beryllium, and lithium fluoride respectively), the (cid:449)hole thi(cid:374)g is o(cid:374)e (cid:373)ole(cid:272)ule so you (cid:272)a(cid:374)"t talk about intermolecular attractions. Ele(cid:272)tro(cid:374)s are al(cid:449)ays i(cid:374) (cid:373)otio(cid:374), (cid:271)ut (cid:449)e (cid:272)a(cid:374)"t tell (cid:449)here they are we have to settle with probability functions (the wave function).

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