IB DP1 ChemistryHL Bonding

What makes atoms join together to make compounds?

Topic 14: Bonding14.1 Shapes of molecules and ions1 hour14.1.1 Predict the shape and bond angles for species with five and six negative charge centres using the VSEPR theory.14.2 Hybridization2 hours14.2.1 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 electrons2 hours14.3.1 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?

2p11st quantum number

2nd quantum number

3rd quantum number

Electron orbital shapes (2nd quantum number)

http://chemwiki.ucdavis.edu/Physical_Chemistry/Quantum_Mechanics/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

1s2 2s2 2p2

Methane sp3 hybridization 2s and 2p3 orbitals hybridize

Ethane, ethene and ethyne

Carbon-carbon bonds  Bond

typeBond energy (kJ/mol)

Bond length (pm)

Hybrid orbitals

ethane single 348 154

ethene double 612 134

ethyne triple 837 120

• Describe and explain the change in bond energy• Describe and explain the change in bond length

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 : sp2 : sp

Ammonia: sp3

Water: sp3

Electrons not associated with a particular atom or bond are delocalized

metallic bond

Benzene, C6H6 ring

Image: http://commons.wikimedia.org/wiki/File:Benzene_resonance_structures.png

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.

A

C

B

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-, CO3

2-, O3