chem bonding Flashcards
what is the formula for lattice energy?
(q+ x q-)/(r+ + r-)
the greater the magnitude of lattice energy, the stronger the ionic bond
lattice energy is the energy released when one mole of a ionic crystaline solid is formed from constituent gaseous ions
why do ionic compounds only conduct electricity in the molten/aq state and not in the solid state?
molten/aq: ions are free to move and act as charge carriers
solid: ions are held in fixed positions and cannot act as mobile charge carriers
the main determinant is the presence of MOBILE charge carriers
Are ionic compounds malleable or brittle?
Hard and brittle
displacement by blows brings ions of like charges opposite each other
like charges repel: strong attraction becomes strong repulsion
how are carbon atoms bonded in diamond?
each C atom is bonded tetrahedrally in a 3 dimensional lattice to 4 other C atoms by forming strong covalent bonds
how are carbon atoms bonded in graphite?
each C atom is bonded to 3 other C atoms in a layered structure by forming strong covalent bonds, with weak intermolecular interactions between layers
weak intermolecular interactions allow layers to slide over each other
what is the requirement for the formation of molecules where the central atom has more than 8 valence electrons?
vacant, low lying orbitals
period 3 and beyond
rank the extent of repulsion in lp-lp, lp-bp and bp-bp repulsion
lone pair, bond pair repulsion
lp-lp > lp-bp > bp-bp
the closer e- pairs are to the central atom, the greater the repulsion
lp attracted by one +ve nucleus are closer to central atom vs bp which are attracted by 2 nuclei
why are e- pairs around the central atom of a molecule are arranged as far apart as possible?
to minimise mutual repulsion
identify the following
1. electron pair geometry
2. molecular geometry
3. bond angle
2 regions of e- density, 0 lp
- linear
- linear
- 180**
identify the following
1. electron pair geometry
2. molecular geometry
3. bond angle
3 regions of e- density, 0 lp
- trigonal planar
- trigonal planar
- 120
identify the following
1. electron pair geometry
2. molecular geometry
3. bond angle
3 regions of e- density, 1 lp
- trigonal planar
- bent
- <120
identify the following
1. electron pair geometry
2. molecular geometry
3. bond angle
4 regions of e- density, 0 lp
- tetrahedral
- tetrahedral
- 109.5
identify the following
1. electron pair geometry
2. molecular geometry
3. bond angle
4 regions of e- density, 1 lp
- tetrahedral
- trigonal pyramidal
- ~107
identify the following
1. electron pair geometry
2. molecular geometry
3. bond angle
4 regions of e- density, 2 lp
- tetrahedral
- bent
- ~105
identify the following
1. electron pair geometry
2. molecular geometry
3. bond angle
5 regions of e- density, 0 lp
- trigonal bipyramidal
- trigonal bipyramidal
- 120 or 90
identify the following
1. electron pair geometry
2. molecular geometry
3. bond angle
5 regions of e- density, 1 lp
- trigonal bipyramidal
- see saw
- <120, <90
<120/90 due to bp-bp repulsion
identify the following
1. electron pair geometry
2. molecular geometry
3. bond angle
5 regions of e- density, 2 lp
- trigonal bipyramidal
- T-shape
- 90
identify the following
1. electron pair geometry
2. molecular geometry
3. bond angle
5 regions of e- density, 3 lp
- trigonal bipyramidal
- liner
- 180
identify the following
1. electron pair geometry
2. molecular geometry
3. bond angle
6 regions of e- density, 0 lp
- octahedral
- octahedral
- 90
identify the following
1. electron pair geometry
2. molecular geometry
3. bond angle
6 regions of e- density, 1 lp
- octahedral
- square pyramidal
- <90
identify the following
1. electron pair geometry
2. molecular geometry
3. bond angle
6 regions of e- density, 2 lp
- octahedral
- square planar
- 90
how does a difference in electronegativity influence the polarity of a bond?
the greater the difference in electronegativity, the greater the bond dipole moment and hence the more polar the bond.
a molecule is polar if its overall dipole moment is NOT zero.
how do instantaneous dipole-induced dipole interactions arise?
they arise as electron movement in particles results in unsymmetrical electron density, resulting in an instanteous dipole that can induce a dipole in a neighbouring molecule.
id-id interactions are short lived and relatively weak.
what are the factors affecting id-id strength?
- no of e-/e- cloud size
- surface area for molecular interaction
more e- means greater e- cloud size: larger e- clouds are more easily polarised, resulting in greater ease of formation of id-id
greater surface are for molecular interaction means greater id-id strength (eg. straight chain vs branched hydrocarbon)
explain the trend in boiling points of halogens
halogens are non polar, so attraction between molecules is id-id. the number of e- increases down the group –> size and ease of polarisability of e- cloud and hence strength of id-id interactions increases down the group.
more energy is required to break stronger intermolecular interactions, boiling point increases down the group.
boiling point: breaking of bonds between molecules (not atoms)
identify: source of bonding
how do permanent dipole-permanent dipole interactions arise?
they arise due to the electrostatic attraction between the delta+ end of one molecule and the delta- end of the other molecule.
what factors affect pd-pd strength?
the size of dipole moments: the greater the differences on e-, the greater the dipole moment and the stronger the pd-pd interaction.
what are the criteria for hydrogen bonding?
- A hydrogen atom covalently bonded to F, O or N
- A lone pair of electrons on an F, O or N atom in an neighbouring molecule bearing a delta- charge
why is ice less dense than water?
each O atom in ice is tetrahedrally bonded to 4 H atoms
* two by covalent bonds and
* two by hydrogen bonds
this enables the water molecules to form rigid, open, 3-dimensional networks
open structure occupies a larger volume for the same mass
why are ionic solids usually soluble in water?
the large amount of energy released in the formation of strong ion dipole interactions can compensate for the energy required to overcome the strong ionic bonds in the solid.
how are σ bonds formed?
the head on overlap of 2 orbitals
how are π bonds formed?
side on overlap of 2 orbitals
where is the π bond e- density situated?
- e- cloud above and below the nuclear axis
- zero e- density along the nuclear axis
where is the σ bond e- density situated?
concentrated between the nuclei of two bonding atoms along the nuclear axis
are σ bonds or π bonds stronger?
σ bond as head on overlap has greater degree of overlap
orbital overlap in a π bond is less effective
why does a cl-cl bond have a greater bond strength than br-br?
(covalent bonding)
- halogen increases in size, valence orbital used in bonding is more diffuse –> overlap of orbitals is less effective
bond energy decreases
what are the 4 factors affecting covalent bond strength?
- number of bonds between atoms (single vs double etc.)
- effectiveness of overlap of orbitals
- differences in electronegativities of bonding atoms (ie bond polarity)
- type of hybridisation of the orbitals of bonding atoms
generally, the stronger the covalent bond, the shorter the bond length
how does covalent character in an ionic bond arise?
attraction of cation results in polarisation of the electron cloud of the anion, pulling it into the region between the two nuclei, resulting in some form of orbital overlap
main point: polarisation of electron cloud results in orbital overlap
what affects the degree of covalent character?
- polarising power of cation (relies on charge density –> the higher the charge density, the stronger the polarising power)
- polarisability of anion (depends on charge and size –> larger e- clouds are easier to distort)
what determines the strength of an ionic bond?
depends on charge and size of ions: lattice energy
what factors affect the strength of metallic bonds?
- no of valence e- from each atom
- charge density
what determines the extent of ionic character in a covalent bond?
bond polarity (electronegativity difference between two bonded atoms)
polar bonds posess partial ionic character
