shapes of molecules and intermolecular forces Flashcards
what shape are molecules with 1/2 e- pairs? bond angle?
linear 180
what shape are molecules with 3 e- pairs? bond angle?
trigonal planar 120
what shape are molecules with 4 e- pairs? bond angle?
tetrahedral 109.5
what shape are molecules with 5 e- pairs? bond angle?
trigonal bipyramid 90 & 120
what shape are molecules with 6 e- pairs? bond angle?
octahedral 90
what effect do lone e- pairs have on bond angles?
orbitals containing lone pairs have a larger electron density and therefore repel more than a bonded pair.
each lone pair reduces bond angle by 2.5 degrees
what is electronegativity?
the ability of an atom to attract the bonding electrons in a covalent bond
what is the Pauling scale?
measures electronegativity
increases up group and along the period
what are polar bonds?
the bonded pair are attracted more towards the atom with the higher electronegativity, giving it a partial negative charge
what is a dipole?
a non-symmetrical molecule with polar bonds
what are permanent dipole-dipole interactions?
when the oppositely charged ends of a dipole attract
this is weak
what are London forces?
electrons move around randomly within the molecule
this induces a temporary dipole
temporary dipoles attract
what affects the strength of london forces?
the no. of electrons
this is why the boiling point increases with electrons
why is hydrogen bonding?
the attraction between a §+h and N,O,F
you draw them with a dotted line
they are very strong
why does water have anomalous properties?
water’s BP and MP are unusually high due to hydrogen bonding
in water, the hydrogen bonds in the open lattice hold the molecules further apart. when ice forms, some break, packing the molecules closer. this is why ice has a higher density.
