bonding Flashcards
explain the VSEPR theory
pairs of outer electrons arrange themselves as far away from each other to minimise repulsion
what is the name given to a molecule with 4 groups of electrons and what will the bond angle be?
eg CH4
tetrahedral
109.5
what is the name + bond angle of a molecule with four groups of electrons, one being a lone pair?
eg - NH3
trigonal pydramidal
107
water has four groups of electrons, 2 being lone pairs
name of shape and bond angle?
v shaped
104.5 because 2 lone pairs means more repulsion
name + bond angle of a molecule with three groups of electrons + no lone pairs?
trigonal planar
120
name and bond angle of a molecule where there are three groups of electrons and one lone pair?
bent / v-shaped
117.5
NOT THE SAME AS WATER BECAUSE WATER HAS 2 LONE PAIRS
name and bond angle of a molecule with 2 groups of electrons
linear
180
name and bond angle of molecule with five groups of electrons
trigonal bipyramidal
90 degrees on one side
120 on other
name and bond angle of molecule with 6 groups of electrons?
octahedral
90
list three types of IMF in ascending order of strength
van der waals
dipole - dipole
hydrogen
where can dipole dipole forces occur?
between molecules with permanent dipoles
molecules with polar bonds
the delta + and delta - regions attract each other to form a lattice structure
why does CO2 not have a dipole moment when it has more than one polar bond?
linear molecule so dipoles cancel out
why do vdW occur between all molecules?
all atoms/molecules positive and negative charges so are NEUTRAL overall
however they produce weak electrostatic attractions
helium has 2 protons and 2 neutrons and is neutral overall,
how can it have a permanent dipole?
at any one time, the electrons could be anywhere
the DISTRIBUTION OF CHARGE is changing at EVERY INSTANT
this means the atom has a dipole at THAT MOMENT
how does an induced dipole occur?
the temporary dipole in one atom then affects the distribution of electrons in nearby atoms to form an induced dipole
this atom is then attracted to the original atom for THAT INSTANT
what would create a larger instantaneous dipole?
more electrons
what does the strength of vdW depend on?
Mr - more electrons and so more IM forces
SHAPE - straight chain molecules have more vdW as they can pack more closely together than branched molecules
what are the conditions required for hydrogen bonding?
a very electronegative atom with a lone pair of electrons covalently bonded to a H atom
(OH or NH group)
why is hydrogen bonding so strong?
Oxygen atoms in water have lone pairs of electrons
Hydrogen atoms are very electron deficient
so…. lone pair of O on one H2O atom is strongly attracted to electron deficient H atom
when do H bonds form?
- when H is covalently bonded to electronegative atom (O or N)
- the H = + charged to form a bond with lone pair from O or N
- angle between OH/NH and H bond must be 180
what is a simple molecular structure?
composed of small molecules (covalent bonding between atoms)
forces of attraction between molecules are much weaker (IMF)
what is a macromolecular structure?
large number of atoms are linked in a regular 3D arrangement by covalent bonds
DIAMOND AND SILICON DIOXIDE
what is a giant ionic structure?
lattice of positive electrons each surrounded in a regular arrangement by negative ions
what is a metallic structure?
regular lattice of positively charged metal ions held together by a sea of delocalised electrons
how can mpt/bpt tell us about the type of structure?
simple molecular compounds = low (all molecular compounds = covalently bonded)
giant structures = high
