Bonding, Intermolecular Forces Flashcards
define ionic bonding
the electrostatic forces of attraction between oppositely charged ions
Why do bonds form?
Because the molecule has a lower energy (i.e. is more stable) than its separated atoms
Why do ionic solids have a non-directional bond?
because oppositely charged ions are attracted to each other in all directions
define covalent bonding
the electrostatic forces of attractions between the shared pairs of electrons and positively charged nuclei of non-metals
define electronegativity
the ability of an atom in a molecule to attract electrons toward itself
how does a polar covalent bonds rise?
the difference in electronegativity of the atoms leads to an unsymmetrical electron distribution
non polar covalent
- electronically symmetrical
- electronegativity difference = 0-0.4
polar covalent
- partial charges
- electronegativity difference<2.0
ionic bond
- full charges
- electronegativity difference>2
define a lewis structure
a representation of covalently bonded molecules
describe VSEPR
Valence Shell Electron Pair Repulsion Model
- observed shapes of molecule arise from each electron group around an atom arranging themselves as far away as possible from other electron groups to minimise repulsions between them
electron group
single bond, multiple (double/triple) bond or lone pair
five electron group arrangements of minimum energy seen in large majority of molecules
- linear (2ED)
- trigonal planar (3ED)
- tetrahedral (4ED)
- trigonal bipyramidal (5ED)
- octahedral (6ED)
describe linear molecules (BP only)
- no of bond pairs
- bond angle
- 3 examples
- shape
- 2 bond pairs
- 180
- BeCl2, CO2 and all diatomic molecules
- straight line
describe trigonal planar molecules
- no of bond pairs
- bond angle
- 1 example
- shape
- 3 bond pairs
- 120
- BCl3
- flat peace-sign
describe tetrahedral molecules
- no of bond pairs
- bond angles
- 1 examples
- shape
- 4 bond pairs
- 109.5
- methane, CH4
- Eiffel Tower
describe trigonal bipyramidal molecules
- no of bond pairs
- bond angles
- 1 example
- shape
- 5 bond pairs
- 90 and 120
- PF5
- fidget spinner shot by an arrow
describe octahedral molecules
- no of bond pairs
- bond angles
- 1 example
- shape
- 6 bond pairs
- 90
- SF6
- christian cross that has been shot by an arrow
why does a lone pair have a greater repulsive effect than a bonding pair?
- lone pair electrons are localised to an atom, so they are closer to each other
state the hierarchy of repulsion
lp to lp> lp to bp> bp to bp
name the 7 types of lone pair inclusive molecule shapes
- trigonal pyramidal molecules
- v shaped/bent molecules
- square planar molecules
- square pyramidal molecules
- seesaw molecules
- t/arrow shaped molecules
- linear molecules
(two very silly Swiss singers terrify Lav)
describe trigonal pyramidal molecules
- which bpo shape are they like
- no of bp, lp, ed
- bond angles
- example
- shape
- like tetrahedral molecules but without top
- 3 bp, 1 lp, 4 ed
- 107
- NH3
- beheaded Eiffel tower
describe v shaped/bent molecules
- which bpo shape are they like
- no of bp, lp, ed
- bond angles
- example
type 1 (SO2 DB):
- like trigonal planar but without top
- 2 bp, 1 lp, 3ed
- 104.5
type 2 (H2O):
- like type 1 but extra pair
- 2 bp, 2 lp, 4 ed
- 104.5
describe square planar molecules
- which bpo shape are they like
- no of bp, lp, ed
- bond angles
- example
- shape
- like octahedral but without both vertical bits
- 4 bp, 2 lp, 6 ed
- 90
- XeF4
- cross laid on its side + 2lp above and below
describe square pyramidal
- which bpo shape are they like
- no of bp, lp, ed
- bond angles
- example
- shape
- like octahedral but without bottom vertical bit
- 5 bp, 1 lp, 6 ed
- 85-87.5
- BrF5
- cross laid on its side + stick up + lp below
describe see saw molecules
- which bpo shape are they like
- no of bp, lp, ed
- bond angles
- example
- like trigonal bipyramidal but without left side bit
- 4 bp, 1 lp, 5 ed
- 87.5-90 (equatorial-axial), 117 (e-e)
- SF4
describe t/arrow shaped molecules
- which bpo shape are they like
- no of bp, lp, ed
- bond angles
- example
- like trigonal bipyramidal but only side 3 + 2 lp
- 3 bp, 2 lp, 5 ed
- 87.5-90
- XeOF2
describe linear molecules (WITH lone pairs)
- which bpo shape are they like
- no of bp, lp, ed
- bond angles
- example
- shape
- like trigonal bipyramidal but only 2 vertical bits
- 2 bp, 3 lp, 5 ed
- 180
- I3-
- straight line
dipole moment
a measure of the separation of charge in a molecule arising from the unequal sharing of electrons in polar bonds
when a dipole is permanent, the molecule is
polar
distinguish between intermolecular and intramolecular forces
intermolecular forces are much weaker than intramolecular forces
4 types of intermolecular forces
- ion-dipole
- dipole-dipole
- hydrogen bonds
- London dispersion forces
what are intermolecular forces important in?
state of matter, solubility, boiling point, melting point
describe an ion-dipole interaction
- interaction between fully charged ion and partial charges of a polar molecule
- the energy of attraction increases with the charge of the ion and decreases with the square of the distance between the ion and dipole
describe dipole dipole interactions
polar molecules attract one another when they orient with unlike charges close together
describe hydrogen bonding
the dipole-dipole interaction that arises when a hydrogen atom is bonded to Nitrogen, Fluorine or Oxygen atoms with a lone pair of electrons
describe dispersion forces
London forces are caused by temporary dipoles which arise in atoms due to uneven distribution of electrons
define what it means for an atom’s electron cloud to be polarisable
- susceptible to distortion by a neighbouring charge
- increases with the number of electrons which increases with molecular mass
