shapes and intermolecular forces

what is the VSEPR theory?

a model used to predict the 3D shape of electrons assuming the electron pairs will arrange themselves as far apart as possible

what does VSEPR stand for

V- valance S - shell E- electron P-pair R-replusion

what is the general formula for a linear molecule

AB2

what is the bond angle for a linear molecule

180

draw a CO2 molecule

what is each multiple bonded treated as

-treated as one bonding region

what is the name of the model with 2 electron pairing regions

linear

what is the name of the model with 3 electron pairing regions

trigonal planar

what is the name of the model with 4 electron pairing regions

tetrahedral

what is the name of the model with 6 electron pairing regions

octahedral

what is the bond angle for trigonal planar

120

what is the bond angle for tetrahedral

109.5

what is the bond angle for octahedral

90

what does a solid line indicate

bond in the plane of the paper

what does a solid wedge indicate

comes out of the plane of the paper

what does a dotted wedge indicate

goes into the plane of the paper

what is a description of a linear molecule

all atoms lie in a straight line

what is the general formula of a trigonal planar molecule

AB3

what is the description of a trigonal planar molecule

three atoms arranged symmetrically

draw BCl3

what is the general formula of a tetrahedral molecule

AB4

draw CH4

what is the general formula of a octahedral molecule

AB6

what is the description of a octahedral molecule

6 atoms are symmetrically arranged around a central atom - one above and one below and 4 in the plane of the paper

what is the general formula of a non linear molecule

AB2E or AB2E2

what are the bond angles in H2O

104.5

what are the bond angles is SO2

118

what is a description of a non linear molecule

two bonded atoms and one or two lone pairs on the central atom

draw H2O

what is the general formula of a pyramidal molecule

AB3E

what is the estimated angle of a pyramidal molecule

107

draw NH3

which bond diagram has 1 lone pair of electrons

pyramidal

which bond diagram has 2 lone pair of electrons

non linear

what is the electron pair repulsion theory

its a model used to explain and predict the shape of molecules and polyatomic ions

what determines the shape of a molecule

electron pairs surrounding the central atom

what does a lone pair of electrons in the valance shell mean

-it is slightly closer to the central atom
-so it occupies more space than a bonded pair
-so it repels more strongly than a bonded pair

what do lone pairs do to the bond angle

-decreace it slightly by 2.5 for each lone pair

the greater the number of electron pairs the…

smaller the bond angle

what is the shape of a NH4+ ion

tetrahedral

draw a NH4+ ion

draw a CO3 2- ion

draw a NO3 - ion

draw a SO4 2- ion

what is the definition of electronegativity

tenancy of an atom to attract electron density towards itself along a covalent bond

what does electron density mean

a pair of bonded electrons

what is a covalent bond

the electrostatic attraction between the nuclei of bonded atoms and the shared pair of electrons

what increases electronegativity

-more protons
-less electron shielding
-smaller atomic radius

what is the most electronegative element

fluorine
-high number of protons
-minimal shielding
-relitrvely low atomic radius

what happens when two covalently bonded atoms have different levels of electronegtiavity

-leads to an imbalance in the dsitrubtion of election density along the covalent bond

what is the dipole moment

the overall direction of a combined dipole

what happens to the dipole moment when the molecule is symmetrical

cancel each other out, making the molecule non polar

what is the definition of a dipole

-seperation in electrical charge so that one atom of a polar covalent bond has a slight positive charge and the other has a slight negative charge

what is a polar covalent bond

a bond with a perminant dipole, having partially positbve and negative charges on the bonded atom

different IMF from strongest to weakest

hydrogen bonds, permeant dipole - dipole, London forces

what are the strength of IMF compared to bonds

they are weak compared to bonds

what causes a permanent dipole - dipole force to form

difference in electronegativity

what causes a London dispersion force to form

uneven distribution of electrons leads to as temporary dipole across the atom which induces another dipole in a neighbouring atom

what causes a hydrogen bond to form

strong dipole dipole attraction between H bonded to a very electronegative atom (NOF)

when do molecules JUST have London forces

when they have equal electrongativety

what is the ripple effect in permeant dipole dipole molecules

the negative dipole from one molecule can attract the positive dipole from another neighbouring molecule

what is the ripple effect in London forces

-once an istanantuous dipole is formed it can induce a dipole in a neighbouring molecule
-however in a split second it is gone and another dipole is gone causing a ripple effect

what causes London forces to sometimes influence boiling point more than other stronger IMF

in large atoms there are more electrons so stronger and more London forces so more energy needed to break them

which molecules cannot make permeant dipole dipole forces

symmetrical molecules

what is broken when you break down a simple molecular structure

the intermolecular forces (London forces)

why is a property of water surface tension

intermolecular forces between water molecules at water surface allow light objects to float

draw two ethanol molecules

what structures do not exhibit any intermolecular force

all giant structures