Module 2- shapes of molecules and IM forces Flashcards
electron pair repulsion theory
electron pairs determine shape of molecule
electron pairs repel so they are as fair apart as possible
shape minimises repulsion giving definite shape
solid line
bond in plane of paper
solid wedge
comes out of the plane of the paper
dotted wedge
goes into the plane of the paper
tetrahedral
4 bp
0 lp
109.5
pyramidal
3 bp
1 lp
107
non linear
2 bp
2 lp
104.5
electronegativity
pauling scale
across PT- nuclear charge increases
- atomic radius decreases
non polar bonds
bonded electron pair shared equally between bonded atoms
- bonded atoms or same
- bonded atoms have same/ similar EN
polar bond
bonded electron pair shared unequally between bonded atoms
- bonded atoms are different
- different EN values
IM forces
weak interactions between dipoles of different molecules
- london forces
- permanent dipole-dipole interactions
- hydrogen bonding
induced DP-DP interactions
weak IM forces
-exist between all molecules
movement of electrons produces changing dipole
instantaneous dipole exists- constantly shifting
dipole induces dipole on neighbouring molecules
induces further dipoles- then attract one another
strength of induced DP-DP interactions
more electrons in each molecule:
- larger instantaneous and induced dipole
-greater the london forces
- stronger the attractive forces between molecules
- increased bp/mp - more energy needed to overcome forces
permanent dipole-dipole interactions
between different polar molecules
simple molecular substance
made up of simple molecules simple molecular lattice (solid)
- held in place by weak IM forces
- atoms within each molecule are bonded together strongly by covalent bonds
