5th - classical bonding Flashcards
octet rule
atoms react to get a full outer shell - most stable e- configuration.
usually main groups: ns2 np6
what is the octet rule based on
empirical obervations
not rlly a rule
doesnt apply to all situations
although bonds are usually called ionic and covalent, irl the bond is usually
between the 2
ionic character and covalent character
what boding do organic solvents dissolve
covalent bonding
ionic bonding structure
regular arrays of cations and anions
what groups does ionic bonding occur between
1 18
2 17
why does ionic bonding occur
the bonded element is usually more stable that the separate ions.
NaCl is more stable that Na+ Cl-
what is ionic bonding based on
electrostatic forces of attraction between the positive and negative charged ions.
why does ionic bonding not occur for d block elements
ionisation energy is too high to remove an electron.
in groups 1, ionisaion energy only increases for successive electrons
where is covalent character seen in ionic bonding
when removing/ transferring more than 2 electrons.
this is due to the increased energy needed to remove it.
covalent character starts to occur
ionic bonding occurs toooo
achieve the octet rule
what is covalent bonding and when does it occur
in groups 13-16
when the IE energy is too high so ionic bonding isnt favoured.
when atoms share electrons in order to achieve the octet rule.
theories in covalent bonding
lewis model: based on electrons as particles (electron pairs)
molecular orbital theory: based on electrons as waves (wave mechanics)
lewis bonding model
chemical bonds consisting of a pair of electrons shared between the 2 atoms (to give a sigma bond)
lewis bnding model double bond
2 pairs of electrons being shared between the atoms
lewis bonding: if smt needs 5 electrons, how many electrons will it put out to share
5
number of bonds = number of valence electrons
wha is the problem with lewis bonding model
aassumes that all valence electrons are equal however they aren’t.
we know p and s arent equal.
bonding = overlap of orbitals
electrons can be in s or p orbitals
sp3 hydrid exp
valence electron is promoted to give 1 electron in each orbital
2s2 and 2p2 gives 2s1 2p3
these 4 are then averaged out to give 4 sp3 orbitals
describe the 4 sp3 orbitals
same size
shape
directionallity
tetrahedral shape
109.5
sp2 hybrids
mix of 2s and 2p orbitals
3sp2 hybrids = trigonal planar 120
unaffected 2p orbital overlaps with other 2p orbital side on to form a double bond
sp hybrids
2 sp hybrid orbitals
2 unaffected 2p orbitals
overlap side on to give a triple bond (2 pi bonds)
we can only average orbitals into hybrids when
the energy of the seperate orbitals are similar
3s 3p 3d are similar
2s 2p 3d arent similar PCl5 breaks octet rule
if bonds are axial and ewuitorial these mean they arent
equal in energy
how can 3rd period elements expand their octet rule
hbridise a dsp3 orbital
due to similar energy
still doesnt rlly work tho bc why is there only 1 d electron
this will also mean the bonds are equal in energy but in PCl5 they arent (2 axial and 3 equatorial)
