Chapter 6 Shapes of Molecules and intermolecular forces Flashcards
what represents a covalent bond in the plane of the paper
a straight line
what represents a covalent bond coming towards you
a triangle
what represents a covalent bond going away from you
a dashed line
why do the covalent bonds go in different directions
to allow the electrons to be as far apart as possible
what does the shape of a molecule depend on
the number of outer shell electrons
what shape do 2 groups of electrons produce
linear shape
what is the angle produced by 2 groups of electrons
180
what shape do 3 groups of electrons produce
trigonal planar
what is the angle produced by 3 groups of electrons
120
what shape do 4 groups of electrons produce
tetrahedral
what is the angle produced by 4 groups of electrons
109.5
what shape do 5 groups of electrons produce
trigonal bipyramid
what is the angle produced by 5 groups of electrons
90 and 120
what shape do 6 groups of electrons produce
Octahedral
what is the angle produced by 6 groups of electrons
90
what do lone pairs do to the shape of a molecule
because they are not bonding they are closer to the nucleus and repel more strongly so for each lone pair the bond angle is decreased by 2.5
what is a ‘pure’ covalent bond
covalent bond where electrons are shared equally
what two factors affect whether a shared electron pair will be closer to an element
charge of the atom
size of the atom
what two qualities will make the shared pair of electrons be closer to the atom
the atom must be bigger and have a greater charge + or -
what is a dipole
unequal changes at either end of an atom
what is a polar bond
bond that has a permanent dipole
what is electronegativity
attraction of the atom for the shared pair of elctrons in a covalent bond
what is the general trend for electronegativity in the periodic table
the furhter right the higher the attraction because they have more protons. going down the attraction decreases because the atom is getting larger
which element always has the highest electronegativity
Fluorine
what happens if the dipoles are equal and symmetrical
the dipoles cancel out
what are intermolecular forces
forces between molecules
what are intramolecular forces
forces within molecules
what does a high electronegtive value mean
strong intermolecular forces and lots of energy is needed to break them
what does a low electronegative value mean
weak intermolecular forces and less energy is needed to break them
what are the three types of intermolecular bonds (in ascending energy order)
induced dipole - dipole
permanent dipole - dipole
hydrogen bonds
what causes an induced/instantaneous dipole - dipole bond
sometimes on random occasion you get more electrons on one side creating an instantaneous dipole which forms a polar molecule
summarise the three qualities of an induced/instantaneous dipole - dipole bond
weak
short lived
present in all things
what 4 factors can make an induced dipole - dipole bond stronger
more electrons
bigger dipoles
stronger attractive forces
more energy needed to break bonds
what is a permanent dipole - dipole bond
a bond where the molecule is always a polar molecule due to electronegativity
give the 4 qualities of giant covalent structures
> no intermolecular forces
high melting and boiling point
insoluble in most solvents due to no attraction with polar molecules
dont normally conduct electricity
give the 5 qualities of simple molecular structures
>weak intermolecular forces >strong intramolecular bonds >low melting and boiling points >non conductors >solubility dependent on polarity and type of solvent
what does immiscible mean
dont mix
what do non polar and polar molecular substances dissolve in
> polar molecular structures dissolve in polar solvents
>non polar molecular structures dissolve in non polar solvents
what is a hydrogen bond
special type of strong permanent dipole - dipole intermolecular force
what 3 bonds do hydrogen bonds occur in
H - F
H - O
H - N
why do hydrogen bonds only occur in three bonds
H - F
H - O
H - N
the three other elements are really electronegatve and quite small
what happens during the hydrogen bond
lone pairs of one molecule bond to the exposed proton of the hydrogen in another molecule forming a very strong permanent dipole
what three things in a molecule do hydrogen bonds affect
boiling point
viscosity
solubility in water/polar solvent
what is viscosity
the stickiness/ lack of fluid in a substance
why is H - O the strongest hydrogen bond
it maximises the most out of its potential hydrogen bond energy because it has the same number of lone pairs as bonding pairs
