Chapter 6 Intermolecular forces Flashcards
intermolecular forces of attraction
weak interactions between dipoles of different molecules
what do intramolecular forces determine compares to intermolecular
intramolecular= identity and chemical reactions of molecule
intermolecular= physical properties of molecules
Induced dipole-dipole forces/ London forces
instantanious dipole caused by temporary uneven distribution of electrons which induces instantaneous dipoles in neighbouring atoms
How is an instantaneous dipole created
Constant movement of electrons so electrons are temporarily unevenly distributed
what does an instantaneous dipole do to its neighbouring atoms
induce several more dipoles leading to attraction
why do larger molecules have stronger london forces between them
They have more electrons so the size of the induced dipoles increase
what does an increase in strength of london forces between molecules cause (melting and boiling points)
higher melting and boiling points
what is the strength of london forces based on
number of electrons
do polar molecules have london forces
Yes but also permanent dipole dipole attractions
Permanent dipole-dipole interactions
ATTRACTION between polar molecules. Opposite dipoles attract one another
are london forces or permanent dipole-dipole interactions stronger
Permanent dipole-dipole interactions
how do simple molecules arrange themselves in a solid
Stack up in a regular structure: simple molecular lattice. Held by weak intermolecular forces
discrete molecule
separate and distinct, no covalent bonds between them
what determines solubility+ general rule
strength of dipole but generally like dissolves like, and the
Physical characteristics of simple molecules x3
Soluble in ‘like’ solution
Dont conduct electricity
Low melting and boiling points
Conditions for hydrogen bonding?
An electronegative atom (negative dipole) of O, N, F with a lone pair of electrons
A hydrogen atom bonded to an electronegative atom
What are hydrogen bonds between
The electronegative atom and the hydrogen which is bonded to an electronegative atom
strength of H bonds compared to other intermolecular forces
Strongest out of the London and permanent dipole-dipole interactions
anomalous properties of H2O
Relatively high melting and boiling point
Ice is less dense than water
Relatively high surface tension
why is water denser than ice
H bonds hold water molecules appart in ice, so the water molecules are further appart than in liquid water
What is the structure that H bonds hold water molecules in in ice
open lattice structure made up of open tetrahedral arrangements
How many H bods can each water molecule form
4
What is the bond angle about each hydrogen in ice
180 degrees
Examples of molecules that can form hydrogen bonds
H2O, HF, NH3
