Structure 2.2.8 + 2.2.9 - intermolecular forces Flashcards
June 6 (28 cards)
Define intermolecular forces
the nature of the force that exsists b/w molecules
what determines intermolecular forces
size and polarity of the molecules
side note: when comparing molecules of the same polarity, the bigger molecule will undergo the larger intermolecular force due to the presence of more e-, which increases charge density
what is the London Dispersion Force (LDF)
-is the only iMF between molecules that are truly non-polar (where the Xe diffrence = 0)
do LDF have dipoles
no bc they dont have real force of attraction
note: e- behave like a cloud, and the cloud density can shift at any moment
what does the shift in electron cloud density create
temporary induced dipole(disappears as fast as its made)
Does the strenght of the LDF increase or decrease with mass
they increase
is LDF present in polar molecules
yes, but often overlooked due to the presence of stronger IMFs
characteristics of molecules w LDF
low mp/bp, many are gases at room temp
insoluble in H2O (no dipoles)
what is dipole-induced dipole
a permanent dipole on a polar molecule can induce a dipole on a neighbouring molecule that is non polar, which results in a temporary dipole (lasts only a moment)
define Dipole-Dipole/ion-dipole attraction
permanent dipole of polar molecules (hence a permanent seperation of charge). +(ions also have a permanent seperation of charge)
what does dipole-dipole/ ion-dipole attraction results in
results in opposite charges on neighbouring molecules or ions, attracting eachother
what does the dipole-dipole/ion-dipole attraction depend on
distance + orientation of dipoles
characteristics of species w dipole-dipole/ion-dipole attraction
higher mp/bp than non polar molecules, and are often liquids or soft solids at room temp
What other force does a substance w dipole-dipole force have, and what are they called together
LDF, and these forces tgt are called van de waals forces
Define hydrogen bonding
is a special, stronger type of dipole-dipole attraction
when does hydrogen bonding occur
when hydrogen is covalently bonded to an especially electronegative element
What does the charge diffrence in hydrogen bonding create
the resulting charge diffrence is so great that it creates a stronger dipole (seperation of charge)
mp and bp of molecules w hydrogen bonding
comparatively higher mp/bp
example of hydrogen bonding
water (H2O)
Mp/bp comparison of LDF, Di-Di, H- bond
LDF<Di-Di<H-Bond
-increases w increasing molecular mass
what structures on average habe the highest mp/bp
giant covalent structures
Define volatility
tendancy of a substance to vapourize
