Molecules: Shapes & Forces Flashcards
define electronegativty
the ability of an atom to attract the pair of e- (the electron density) in a covalent
what affects electronegativity - 3 tings
nuclear charge
atomic radius
electron shielding
what is the most electronegative element
Fluorine - 4.0
largest nuclear charge for its electron shielding, small atomic radius
how do you get a non-polar bond
when both bonding elements have electron under 0.5
when do you get a polar bond
when both bonding elements have a electronegativity difference of more than 0.5
what is are the 3 types of intermolecular forces
hydrogen bonding
van der Waals
permanent dipole-dipole
what is the strongest type of intermolecular force
hydrogen bonding
what is the weakest type of intermolecular force
van der Waals
describe van der waals forces of attraction
TEMPORARY dipoles are created by the random movement of electrons
induces a dipole in the neighbouring molecule
force is stronger in larger molecules b/c more electrons
describe permanent dipole-dipole attraction
some molecules with polar bonds have permanent dipoles - forces of attraction between those dipoles and those of neighbouring molecules
what conditions are needed for hydrogen bonding to occur
O-H, N-H, F-H bonds, lone pair of e- on O F N
BECAUSE O, N, and F are highly electronegative, H nucleus is left exposed
strong forces of attraction between H nucleus and lone pair of electrons on O, N, F
what does the shape of molecules depend on
number of electrons in the valence shell of central atom
and the number of these electrons which are in bonded or lone pairs
what does the electron pair repulsion theory state
e- pairs will take up positions as far away from each other as possible
what is electronegativity measured on
the pauling scale
how does atomic structure affect the electronegativity
as atomic radius increases
bonding pair of e- become further from the nucleus
tfore, less attracted to the +tive charge of nucleus
tfore, less electronegativity
how does the number of protons affect electronegativity
more protons,
more attraction to e- in covalent bond
higher electronegativity
what is the trend of electronegativity down a group
decreases
b/c
atomic radius increases
shielding increases
ionic formula of
- hydroxide
- sulfate
- nitrate
- carbonate
- ammonium
- OH-
- SO4 2-
- NO3 -
- CO3 2-
- NH4 +
shape and bond angle when
2 bonded pairs + 0 lone pairs
linear
180 degrees
BeCl2
shape and bond angle when
3 bonded pairs + 0 lone pairs
trigonal planar
120 degrees
BF3
shape and bond angle when
4 bonded pairs + 0 lone pairs
tetrahedral
109.5 degrees
CH4
shape and bond angle when
5 bonded pairs + 0 lone pairs
trigonal bipyramid
90 and 120 degrees
shape and bond angle when
6 bonded pairs + 0 lone pairs
octahedral
90 degrees
shape and bond angle when
2 bonded pairs + 1 or 2 lone pair
bent
1 lone pair = 118 degrees
2 lone pairs = 104.5 H20
shape and bond angle when
3 bonded pairs + 1 lone pair
trigonal pyramid
107 degrees
NH3
what effect does adding a lone pair have on the bond angle
each lone pair decreases the bonding angle by 2.5 degrees
number of bonding pairs and lone pairs in a linear molecule
2 bp
0 lp
number of bonding pairs and lone pairs in a trigonal planar molecule
3 bp
0 lp
number of bonding pairs and lone pairs in a tetrahedral molecule
4 bp
0 lp
number of bonding pairs and lone pairs in a trigonal bipyramid molecule
5 bp
0 lp
number of bonding pairs and lone pairs in an octahedral molecule
6 bp
0 lp
what does a straight line represent in 3D bond representations
straight line = normal bond
bond lies in the plane of the paper
what does a dashed line represent in 3D bond representations
bond extends backwards away from viewer
into the paper
what does a wedged line represent in 3D bond representations
bond protudes forwards towards viewer
when asked in an exam to draw bonds do you draw 2D or 3D shapes
2D if asked anything about bonds
3D if asked anything about shape
