intermolecular forces Flashcards
define intermolecular forces
amount of force between neighbouring molecules
what are intermolecular forces caused by
weak attractive forces between small dipoles in different molecules
what are the 3 types of intermolecular forces
permanent dipole dipole interactions
van der waals forces
hydrogen bonding
define a permanent dipole dipole force
the weak attractive force between permanent dipoles in neighbouring polar molecules
if you increase the number of electrons what does this do to the strength of the van der Waals forces
increased number of electrons = increased strength of van der Waals forces
explain why electronegativity increases as you go to the right of the periodic table in terms of the size of the positive charge on the nucleus
number of protons increases
so increased positive charge increases
the increased attraction between the nucleus and the pair of electrons in the covalent bond
so elements on the right are more electronegative
explain why electronegativity increases as you go to the right of the periodic table in terms of atomic radius
smaller atomic radius means the closer the bonding electrons will be to the nucleus of an atom
so elements on the right as more electronegative
explain why electronegativity increases as you go to the right of the periodic table in terms of shielding
electrons in inner shells shield the electrons in the outer shells from the positive charge of the nucleus
so greater number of inner shells decreases electronegativity but as you go to the right in the same period it stays constant
why do atoms with more electrons have a higher boiling point
more electrons = stronger van der waals forces
what are van der waals forces caused by
the random movement of electrons
(every atom/molecule will experience van der waals forces)
if you place one atom with van der Waals forces next to another atom what will it do
it will induce a dipole in atom 2 with the opposite facing charges therefore both atoms now experience van der Waals forces
if you decrease electronegativity what happens to the strength of permanent dipole dipole forces
decrease electronegativity = decreased strength of permanent dipole-dipole forces
to experience a permanent dipole dipole interaction what must both molecules have?
a permanent dipole
what 2 conditions are needed for hydrogen bonding to take place
- hydrogen atom bonded to a strongly electronegative atom
- electronegative atom must have at least 1 lone pair of electrons
what atoms can bond with hydrogen and undergo hydrogen bonding
fluorine
oxygen
nitrogen
(all 3 are very electronegative and have at least 1 lone pair)
explain the bonding in hydrogen fluoride
fluorine has 3 lone pairs
and fluorine is the most electronegative atom so this strongly attracts the pair of electrons in the covalent bond so it is a polar molecule
hydrogen bonds form between the hydrogen on the right being attracted to the lone pairs of fluorine on the left molecule
why is ice floating important for organisms living under water
insulates the water below preventing the water from freezing completely
why does ice float
in ice the water molecules are further apart than in liquid water therefore it is less dense which allows it to float
what do water molecules do at freezing point
arrange themselves into an ordered structure stabilised by a network of hydrogen bonds1
in liquid water what happens in terms of hydrogen bonds
hydrogen bonds are constantly being being/formed due to the movement of water molecules
why does water have a relatively high melting point
takes a lot of energy to break the hydrogen bonds
iodine is non-polar what type of solvent does it dissolve in? what happens in terms of solvent molecules?
iodine non polar molecule so dissolves in a non polar solvent
solvent molecules move from van der Waals forces to the iodine molecules
