Bonding and Molecular orbital theory - valence bond theory Flashcards
wave function and probability explanation
the probability density of an electron within an orbital can be found from squaring the wave function.
core atomic orbitals definition
The orbitals which aren’t in the valence electron energy shell which don’t contribute towards the bonding or an atom.
valence orbitals
The occupied orbitals in the highest electron energy shell which contribute towards the bonding of an atom
exothermic reaction definition
a reaction which releases heat energy with a negative enthalpy change
endothermic reaction definition
a reaction which absorbs heat energy with a positive enthalpy
bonds breaking in bond enthalpy
requires heat energy to be absorbed, which means endothermic
which means positive enthalpy
bonds forming bond enthalpy
requires heat energy to be released, which means exothermic
which means negative enthalpy
bond enthalpy calculation
bonds of reactants - bonds of products.
enthalpy symbol and unit
ΔH = kJ/mol
requirements for valence bond theory
atomic orbitals with one electron present must overlap.
These overlapping orbitals must have the same sign.
covalent bond strength rule
the greater the area of overlap for two atomic orbitals relative to the total area of both orbitals, the greater the covalent bond strength.
σ bond definition
a bond formed by the end on overlap of s or p orbitals, which produces a bond with no nodal planes and bond axis symmetry.
nodal plane definition
an area within an orbital where there is no probability of finding an electron.
orbitals which can form σ bonds
s and p orbitals
sign on an s orbital
must always be positive since the wavefunction cannot be negative.
π bond definition
A bond formed from side on overlap of two p orbitals, which will contain a nodal plane on the bond axis and be assymetrical around the bond axis. .
rule for the sign of a π bond
when you rotate the π bond 180 degrees around the bond axis the sign changes due to the nodal plane.
Homonuclear molecules
a molecule comprised of 2 or more identical atoms
valence bonding for homonuclear molecules
use normal electronic configuration
when 1 p orbital is half filled make a σ bond.
every p orbital after that you must make a π bond
two types of valence bond theory
normal structure and hybrid structure
normal electronic structure in valence bond theory
uses normal electronic structure to determine number of bonds formed and bond structure.
advantages of normal electronic structure in valence bond theory
it will get the energy of all the different types of orbitals correct
disadvantages of normal electronic structure in valence bond theory
it will get the bond angle and geometry incorrect.
hybrid orbital theory in valence bond theory
change the electronic structure to suit VSEPR rules, then find the number of bonds based on the new electronic configuration.
advantage of hybrid orbital theory in valence bond theory
it will accurately predict the bond angles and geometry in a molecule
disadvantage of hybrid orbital theory in valence bond theory
the energy of orbitals will not necessarily be correct.
hybridisation definition
where atomic orbitals of different shapes and energies are mixed to form a set of degenerate orbitals with the same structure.
sp3 structure
tetrahedral
sp2 structure
trigonal pyramidal with a 2p orbital perpendicular to the hybrid orbitals.
sp structure
linear with two 2p orbitals perpendicular to the hybrid orbitals.
process of producing hybrid orbital structure
use VSEPR to find arrangement of valence electron pairs.
choose correct hybridisation
make hybrid orbitals degenerate and apply Hund’s rule.
draw out structure.
sp3 bond type
single bond
(σ)
sp2 bond type
double bond
(σ + π)
sp bond type
triple bond
(σ + 2π)
how are σ bonds formed in hybridisation
from overlap of hybrid orbitals of the same sign.
how are π bonds formed in hybridisation
from overlap of 2p orbitals perpendicular to the hybrid orbitals.
rule for atoms with lone pairs and atoms with electron deficiency
atoms which are electron deficient and atoms which have lone pairs can form dative covalent bonds if the unoccupied orbital and the orbital containing the lone pair have the same sign.
