Intermolecular Forces Flashcards
Intramolecular forces
- Forces that physically keep substances together
- Ionic and molecular bonds
- Determines the chemical behaviors of a substance
Intermolecular force
- Attraction between molecules
- Ionic molecules do not form intermolecular bonds
Importance of intermolecular forces
- Molecular compound properties can not be explained just through covalent bonds
- If covalent bonds were the only forces, molecular compounds would be gasses
- This is because the molecules are not strong enough to hold them to solids or liquids
- They are not interacting (intermolecular bonds)
Trend of Intermolecular forces
- When intermolecular forces between molecules in molecular compound increase (held tighter and closer), the compounds melting, boiling and surface tension also increase
Electrostatic forces
- Full charges you need to separate, which makes it difficult
- Forces made by Ionic crystal
Molecular polarity
Used molecular polarity determines what the molecule can do
Dipole-Dipole Force
- Polar has different ends
- If you have another molecular, the opposites sides will attract
- It does not have to be the same molecular (has to be a pure substance)
Hydrogen bond
- When hydrogen is bonded on the FON
- Type of dipole-dipole force
Ion-Dipole Force
- The polar molecule is attracted to the cation/anion
- The opposite side get attracted
The strength of Ion-Dipole force depends
charge and size of the ion
- Cations are stronger due to being smaller (concentrated energy)
Magnitude of diploid
- You can find the strength by finding electronegativity of atoms
London Dispersion Force
- All molecules have this intermolecular force
- Only temporary (happens for a second)
How does London Dispersion Force work
Electrons move around in molecules and can move to one side of molecules
* This forms temporary dipoles
* This induces other molecules to form temporary diploses (due to attraction)
* This creates a temporary attraction to all molecules in a compound
2 factors to determine strength of LD force
Number of electrons
- Greater electrons= more chance of forming temporary dipole= stronger LD force
Shape of the molecules
- More elements in linear shape, more surface area with adjacent molecules = stronger LD force
Intermolecular Forces & States
- Responsible for different states of matter
- Stronger intermolecular forces= high melting/boiling point
- Liquids and gasses are able to move more freely (less interactions)
- Must have enough kinetic energy to break intermolecular forces (energy/temp), allowing more space
Intermolecular Forces & Water Solubility
- Water must interact with polar molecular or ion to dissolve
- Oxygen with cation and hydrogen with anion
Water in different forms
Water is less dense as a solid than liquid
* When water freezes, molecules lose kinetic energy and slow down
* Molecules are able to interact with each other and form hydrogen bonds
* Hydrogen bonds will arrange in crystal structure
* This creates more space between molecules
* Liquid molecules are more closer because the solid forms hydrogen bonds
Water and surface tension
- Hydrogen bonds in water hold strongly and pull together
- This resist them from breaking and creates a shape to create smaller surface area
- This is because they want to be closer together (hydrogen bonds)
Strongest forces
- Hydrogen bonding
- Dipole dipole
- London dispersion
