intermolecular forces Flashcards
What happens when a molecule is vapourised?
the intermolecular forces are broken not the covalent bonds
What is the relationship between the intermolecular forces and the volatility of a substance?
The volatility of a liquid decreases as the number and strength of the intermolecular forces increases
What are induced dipole-dipole forces (london forces)?
induced d-d forces are attractive forces between molecules that arise when random electron movements in one molecule cause and instantaneous dipole which causes an induced dipole on another molecule
How are induced dipole-dipole forces formed?
1.random movements of electrons causes excess electron density on one side of the molecule = instantaneous dipole
2. there’s an attraction between instananeous and induced dipoles
What is a permenant dipole-dipole bond?
when molecules have atoms of different electronegativites so the electrons are not equally shared
What type of intermolecular force do polar substances have?
permenant dipole-dipole - higher MP and BP than non-polar substances
What is a hydrogen bond?
the intermolecular attraction between hydrogen covalently bonded to N,O or F on one molecule and the lone pair on N,O or F on another molecule
What does the metal hydrides BP graph show about hydrogen bonds?
the hydrides of O,N or F are not part of the trend because of hydrogen bonds = need more enegry to break H bonds
What are the 3 anamolous properties of water?
relatively high MP and BP
high surface tension
less dense as a solid
Why does water have a high MP and BP?
more energy is needed to break H bonds - strongest bond
Why is water less dense as a solid than a liquid?
it has an open lattice structure so the spaces between molecules are larger than in a liquid h2O
Why does water have a high surface tension?
takes a lot of energy to disrupt H bonding in the layer of molecules at the waters surface
What are some simliar molecules to water with H bonds?
ethanol CH3CH2OH
ammonia NH3
What makes a substance soluble in water?
the ability to form H bonds - water attaches to the molecule by H bonds
Why does a permenant dipole-dipole interaction cause a high MP and BP?
theres an electrostatic attraction between molecules
