Molecular Bonding Flashcards
Describe aspects of Lewis Theory
- IONIC
- COVALENT
BONDING uses VALENCE e-s
VSPER
FORMAL CHARGES
Ionic: valence e- transfer from metal to non-metal to achieve OCTET.
Covalent: valence e- pairs shared between atoms to achieve OCTET.
BONDING & LONE PAIRS.
Define electronegativity
tendency of an atom to attract a bonding pair of electrons
What is formal charge?
Formal charge = valence e-s - (lone pair e-s + 1/2 bonding e-s)
What is a polar covalent bond?
Unequal sharing of e-s due to difference in EN.
What is an ATOMIC ORBITAL?
Area around a nucleus where e-s are likely found.
State the shape of an s AO.
SPHERICAL
State the shape of a p orbital
DUMBELL
What is a NODE?
Region of ZERO probability of finding an e-
Where waves of opposite phases DESTRUCTIVELY overlap & cancel.
Compare the energy of a p & s orbital
p orbital HIGHER ENERGY than s
Describe the shape of a p orbital
DUMBELL split by a NODAL PLANE into 2 lobes.
3 DEGENERATE p AOs w symmetry about x, y, z axes.
Why do AOs combine to form MOs?
To achieve a MORE STABLE, LOWER ENERGY state.
Describe the MO theory
AOs combine to MOs.
Aufbau principle states…
e-s fill lowest energy orbitals first.
Pauli exclusion principle states
max. 2 e-s occupy an orbital, of opposite spins
Hund’s rule states
for degenerate AOs, e-s occupy empty orbitals first
antibonding orbitals:
e-s NOT located between 2 distinct nuclei
HIGHER ENERGY
bonding orbitals:
HIGH e- DENSITY between nuclei.
LOWER ENERGY
Compare energy states of bonding & anti-bonding orbitals
AB > B
END ON OVERLAP forms __ bonds
σ bonds
SIDE-TO-SIDE OVERLAP forms __ bonds
∏ bonds
Compare strength of σ & ∏ bonds
σ > ∏
HOMO =
Highest Occupied Molecular Orbital - filled MO highest in energy
LUMO =
Lowest Unoccupied Molecular Orbital - empty orbital above HOMO.
DESTRUCTIVE CANCELLATION ->
No e- density between 2 nuclei
ANTIBONDING
CONSTRUCTIVE
e- density between 2 nuclei
BONDING
Hybridisation of: C-C bond
sp3-sp3
Hybridisation of: C=C bond
sp2-sp2
Compare C-C and C=C bond length & strength
C=C shorter & stronger
Hybridisation of: C≡C
sp-sp
Hybridisation of: AMMONIA
sp3-s N-H overlap
sp3 bonds are
σ ONLY
sp2 bonds are
σ & ∏
sp bonds are
σ & ∏
Describe INDUCTIVE EFFECT
Atoms ability to polarise a bond
DIPOLE MOMENT
NET POLARITY of a molecule
D = e x d
Hydrogen Bond Donor
ELECTRON DEFICIENT H
Hydrogen Bond Acceptor
ELECTRON RICH HETEROATOM
State 2 possible ethane conformations
STAGGERED or ECLIPSED
What is TORSIONAL STRAIN
Repulsion between bonding e-s of adjacent substituents
Which conformation is more stable: staggered ir eclipsed
STAGGERED
Expand on ‘molecules are not static’
MANY INTERCONVERTING CONFORMERS can exist mutually at a time.
ANGLE STRAIN
Deviation from ideal geometrical bond angle
TORSIONAL STRAIN
repulsion of proximate bonding e-s
STERIC STRAIN
atoms/groups approach too closely
State the NEAR STRAINLESS CONFORMATION
CHAIR
- no angular/torsional strain
Compare boat & chair strain
Boat more strained
What is a ‘ring flip’
Chair conformational can interconvert for cycloalkanes - exchange of axial/equatorial positions.
