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Inter Molecular Forces (IMFs) (Ionic Substances (properties (water soluble…
Inter Molecular Forces (IMFs)
Intermolecular vs Intramolecular forces
Intramolecular
hold atoms together in molecules
high energy levels (difficult to break)
different types based on electron clouds
ionic- transfer of electrons
covalent- shared electrons, can be polar or nonpolar
Intermolecular
hold molecules together
weaker than intramolecular forces
include ion-dipole, hydrogen bonds, dipole-dipole forces and LDFs
IMF Rules
Weak IMFs
gases at room temp
low melting/boiling points
Strong IMFs
high melting/boiling point
solids at room temp
Types of IMFs
Dipole-dipole forces
When the molecules are polar
Hydrogen Bonds
When there is a direct bond between a hydrogen and a F O or N atom.
These bonds are highly electrostatic
London Dispersion Forces
Weakest of the four
(in my own words): basically asince the location of electrons in any given atom is random (remember the orbitols?), the odds of the electrons not being evenly distributed throughout the atom is usually pretty high. Because of this, one part of the atom will have a partially negative charge and the other part will have a partially positive charge. The partially positive side will attract the electrons from neighboing atoms, which will make electrons go to one side of another atom, and therefor causing that one to have a partially negative charge and partially positive charge... and so on.
strength depends on
electron cloud
polarizability
how easy it is for the atom to form the instantaneous dipole
molar mass
Ion-Dipole Forces
(in my own words): This is the result of a solution. When two substances are mixed together that are polar, there will be a positive and negative ion that will attract its respective counterpart of the other polar molecule.
strongest of the four
Surface tension
Molecules form IMF bonds with each other in order to stay in their state, like a liquid
Surface tension occurs because the molecules at the surface of a liquid do not have enough bonds to cancel out all the other bonds.
Pretty much, the molecules at the top of the liquid are being pulled down and sideways, but not up, so they try to minimize surface area to stay stable.
Viscosity- a liquid's resistance to flow
Strong IMF- higher viscosity
Weak IMF- low viscosity
Vapor Pressure- pressure exerted by a vapor over a liquid
Strong IMF- low vapor pressure
Weak IMF- higher vapor pressure
This is because VP comes from how
volatile
the substance is- how quickly it evaporates.
Electronegativity
the power that the negative part of a molecule attracts the positive part
Unequal electronegativity= polar molecule
Ionic Substances
Made up of ions
held together by ionic bonds
properties
water soluble
conducts electricity ONLY if melted or dissolved
insoluble in NON-POLAR solvents
high melting point
metal and nonmetal formula units
Molecular
Non-polar molecules
covalent bonds
dispersion forces
low melting and boiling point
nonconducting, insoluble in water
polar moleculaes
forces
dispersion forces
dipole
hydrogen bonding
nonconducting
higher melting and boiling point (than NP molecular)
nonmetal molecules
Covalent Network Solids
made of atoms
covalent bonds
properties
VERY high melting point
non-conductors
hard, solid
insoluble in common solvents
made of metalloids and/or nonmetal ATOMS (not molecules)
Metallic
Basically just a sea of cations (metal atoms) in "a sea of delocalised electrons." Electrons are just kind of scattered around and cations are floating through them
properties
variable melting points
insoluble in common solvents
CAN react with water
malleable, ductile, good conductors
metallic bonds
metal atoms
Rules
WATER can never be hotter than 100 degrees C
ICE- can never be colder than 0 degrees C
What it means to induce a dipole
A dipole is when part of an atom/molecule is partially positive and partially negative.
In order to "induce" a dipole, there must be a negative pull on one side, that will draw a positive pull from another atom/molecule
this is how LDFs work; they basically draw out a positive charge from their surrounding atoms. This is also why they can be called "Dipole Induced Interactions"
Key Numbers
Water's heat of fusion (p sure thats what its called) is 6.02 kJ fir every mol of water heated
heat of fusion= solid to liquid
Water's heat of vaporization: 40.7 kJ per mol of water
heat of vaporization= liquid to gas