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Structure & properties. INTERMOLECULAR FORCES. INTRAMOLECULAR FORCES. Ionic bonds, covalent bonds, metallic bonding are all examples of bonds within a molecule. intermolecular forces. Forces BETWEEN molecules Weaker than inTRAmolecular forces, but still very important. - PowerPoint PPT Presentation
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Structure & propertiesINTERMOLECULAR FORCES
INTRAMOLECULAR FORCES
Ionic bonds, covalent bonds, metallic bonding are all examples of bonds within a molecule
intermolecular forces
Forces BETWEEN molecules
Weaker than inTRAmolecular forces, but still very important
QuickTime™ and a decompressor
are needed to see this picture.
intermolecular forces!• Featuring the exciting world of ...
• Dipole dipole, hydrogen bonding, ion dipole, Van der Waal’s/London dispersion forces!
dipole-dipole
One of the strongest of the intermolecular forces
Result from uneven distribution of electrons, creating a dipole
Molecules will arrange themselves in solution according to the dipoles present
ie) ICl
impact on mp/bp
Dipoles will INCREASE melting and boiling points
The molecules are now stuck together more tightly (opposites attract!) and so more energy is required to melt/boil the substance
hydrogen bondingA special type of dipole that only occurs between hydrogen and F, O, N atoms
Usually represented by a dashed line
One of the reasons water has such a high boiling point is this interaction
Impact on mp/bpConsider the effect hydrogen bonding has on melting and boiling points
state at room
Tboiling point
(°C)H2O liquid 100H2S gas -61CH3–O–CH3 gas -24CH3–CH2OH liquid 78NH3 gas -28PH3 gas -90HF gas 21HCl gas -79CH3COOH liquid 118C2H6 gas -89
ion dipole forces
- force of attraction of ion and polar molecule- ionic compounds dissociate in polar solvents since ion (cation/anion) dipole (polar molecule) force overcomes force binding ions together
- ex) NaCl dissolved in water
Think about it! • You are making some pasta. The
instructions indicate you should boil the pasta in salted water.
• You are in a rush and want to eat as quickly as possible!
• Should you add salt BEFORE you boil the water or AFTER the water has started to boil?
• Explain why!
van der waal’s forcesThese occur in every molecule!
At any given time, there may be more electrons in a particular area than another, creating an ever-so-slight dipole
This creates a chain reaction which can have a large effect in molecules
impact
The impact is larger with larger molecules, since there more electrons and a higher chance they will be unbalanced
Who has the highest bp? H2O vs H2S H2O due to hydrogen
bonding,
NH3 vs PH3 NH3 due to hydrogen bonding
CHCl3 vs CH4 CHCl3 due to dipole-dipole
CH4 vs C10H20 C10H20 due to larger VDW forces
try it!
try it!
Nelson Chemistry 12
Read p.257-265
Try p.260 #1-5; p.264 #9,11