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TOPIC 5: THEORY OF CHEMICAL BONDING - Coggle Diagram
TOPIC 5:
THEORY OF CHEMICAL BONDING
Valence Bond Theory:
that a covalent bond is formed by the pairing of two electrons with opposing spins in the region of overlap of atomic orbitals between two atoms
(more extensive the overlap between two orbitals, the stronger is the bond between two atoms)
Sigma bond:
~Overlapping of one s orbital with another s orbital
~Overlapping of one s orbital with a p orbital
~Head on overlapping of one p with another p orbital
Pi bond:
~produced by the sideways overlapping of one p orbital with another p orbital.
Overlap of an
empty orbital
with a
fully-filled orbital
leads to the formation of a co-ordinate covalent bond or dative bond
A molecule is a group of atoms bound together through localized overlap of valence-shell atomic orbitals
Each atoms in a molecule retain its AO in a molecule
Molecular Orbital Theory (MOT):
~Localized electron model (VSEPR theory and hybridization) is of great value in interpreting the structure and bonding of molecules.
~
atomic orbitals
of separated atoms are combined into
molecular orbitals
Problems with this model:
~incorrectly assumes that electron are localized and so the concept of resonance must be added
~does not deal effectively with molecules containing unpaired electrons
~The model gives no direct information about bonding energies
Orbital Mixing:
combination of atomic orbitals forming molecular orbitals
orbitals to mix they must:
~Have similar energy levels.
~Overlap well (similar orientation).
~Be close together.
A molecule is a collection of nuclei with the electron orbitals delocalized over the entire molecule
Mixing of AO forming MO with a given energy and shape that are occupied by the molecule’s electrons
The number of molecular orbitals (MOs) formed is always equal to the number of atomic orbitals combined.
The more stable the bonding MO, the less stable the corresponding antibonding MO
BOND ORDER
bond strength:
Larger bond order means greater bond strength
number of bonds that exist between two atoms.
existence of molecules or ions
Valence Shell Electron Pair Repulsion(VSEPR) THEORY:
Electron groups around the central atom will be most stable when they are as far apart as possible
Two geometries for each molecule
Electron-group geometry:
Determined by the locations of regions of high electron density around the central atom(s)
The mutual repulsions among electron groups lead to an orientation of the groups that is called
electron-group geometry
Geometry is unaffected by lone pairs of electrons
The Effect of Nonbonding Electrons:
the bond angle decreases as the number of lone pairs increases
Molecular geometry(shape of a molecule):
Determined by the arrangement of atoms around the central atom(s
the bond angle decreases as the number of lone pairs increases(possible for a molecule to contain polar bonds, but not be polar.)
The overall polarity of a molecule depends on its molecular geometry.
VSEPR notation:
~Central atom in a structure is denoted as A
~Terminal atoms as X
~Lone pairs of electrons as E
Hybrid Orbitals:
concept that helps explain how atoms combine to form molecules
Hybridization of Atomic Orbitals:
Hybridization is the process by which
atomic orbitals
from the same atom combine to form new hybrid orbitals that are energetically equivalent.
Covalent bonds formed by the end-to-end overlap of orbitals, regardless of orbital type, are called sigma (s) bonds. All single bonds are sigma bonds