IB DP1 Chemistry
HL Bonding
What makes atoms join together to make compounds?
Topic 14: Bonding
14.1 Shapes of molecules and ions
1 hour
14.1.1 Predict the shape and bond angles for species
with five and six negative charge centres using the
VSEPR theory.
14.2 Hybridization
2 hours
14.2.1 Describe σ and π bonds.
14.2.1 Describe σ and π bonds.
14.2.2 Explain hybridization in terms of the mixing of
atomic orbitals to form new orbitals for bonding.
14.2.3 Identify and explain the relationships between
Lewis structures, molecular shapes and types of
hybridization (sp, sp2 and sp3).
14.3 Delocalization of electrons
2 hours
14.3.1 Describe the delocalization of π electrons and
explain how this can account for the structures of
some species.
Schrodinger wave equation
Which energy level is an electron in?
1st
quantum
number
2nd
quantum
number
1
p
3rd
quantum
number
Electron orbital shapes (2nd quantum
number)
http://chemwiki.ucdavis.edu/Physi
cal_Chemistry/Quantum_Mechan
ics/Atomic_Theory/Electrons_in_
Atoms/Electronic_Orbitals
Electron energy levels
Hybridization
atoms  circular electron shells 2,8,8,…orbitals s,p,d,f,…
 s, p, d, f orbitals only for single atoms in gaseous state
 hybridization
 electron orbitals change shape (and energy) during bonding
σ-bond
 strongest form of covalent bond
 orbitals overlap on line between nuclei
 commonly s+s, pz+pz, s+pz
Image: http://en.wikipedia.org/wiki/Pi_bond
π-bond
 orbital overlap not on line between nuclei
 usually weaker than sigma bonds
 stop rotation
Image: http://en.wikipedia.org/wiki/Pi_bond
Orbital shapes of spdf orbitals and hybrid ized
orbitals
Image: http://en.wikipedia.org/wiki/Pi_bond
Electronic configuration of carbon
2
2
2
1s 2s 2p
Methane sp3 hybridization
 2s and 2p3 orbitals hybridize
Ethane, ethene and ethyne
Carbon-carbon bonds
Bond
type
ethane
single
Bond
energy
(kJ/mol)
348
Bond
length
(pm)
154
ethene
double
612
134
ethyne
triple
837
120
• Describe and explain the change in bond energy
• Describe and explain the change in bond length
Hybrid
orbitals
Single bond (ethane)
 one axial C-C s -Bond
 Hybridisation: one s-orbital and three p-orbitals  four sp3-orbitals
 The sp3-orbitals have a tetrahedral shape (109.5o).
Double bond (ethene)
 one axial s -bond and one offset p-bond
 Hybridisation: one s-orbital and two p-orbitals  three sp2-orbitals
 The sp2-orbitals have a trigonal planar shape, 120o
Triple bond
 One axial s -bond and two offset p -bonds
 Hybridisation: One s-orbital and one p-orbital  Two sp-orbitals
 The sp-orbitals give a linear shape
The shape of the hybrids corresponds to the
structure given by VSEPR / Lewis structure.
 Ethane : Ethene : Ethyne
sp3
:
Ammonia: sp3
Water: sp3
sp2
:
sp
Electrons not associated with a particular
atom or bond are delocalized
metallic bond
Benzene, C6H6 ring
B
A
The p-bond in the double
bond can switch place
Electrons are delocalized.
A and B: resonance
structures.
C: resonance hybrid.
Molecule gains resonance
energy by delocalizing
electrons.
C
Image: http://commons.wikimedia.org/wiki/File:Benzene_resonance_structures.png
Resonance bond
 Resonance describes delocalized electrons within some
molecules or polyatomic ions where the bonding cannot be
expressed by one single Lewis formula.
 A molecule or ion with such delocalized electrons is
represented by several resonance structures.
Draw the structures of NO3-, CO32-, O3