VBT, IFs, Properties/Structures of Solids, MOT

Electron Domains/Steric #

total # of e- pairs (lone + bond pairs)

Electron Domain Geometry

# of lone pairs + bond pairs

e.g. AX2E2 e- domain geometry = tetrahedral (4 pairs = steric # 4 = tetrahedral)

Molecular Geometry

only # of bond pairs

e.g. AX2E2 molecular geometry = bent

Bonding Domains

bond pairs

Non-Bonding Domains

lone pairs

Valence Bond Theory

model of bonding

bonding e- pairs are located between bonding atoms

non-bonding e-pairs are located in regions outside the bonding region

Valence bond theory only applies to what cpds?

covalent

Valence bond theory does not work well for __________ atoms.

hypervalent (e.g. SF6)

Draw the VBD for H2

solution in notebook

Draw the VBD for HF

solution in notebook

σ bond/end-to-end overlap

bond between two nuclei where bonding e- line up along the internuclear axis

Internuclear Axis

horizontal line that goes through the nucleus

To be able to form a covalent bond, the atom has to be able to _____ and __ an e-.

offer, receive

The first pair of e- to form a covalent bond is a _ bond. Therefore in covalent bonding, _ bonds are ALWAYS present.

σ, σ

Draw the VBD for F2

solution in notebook

Hybridization

e- being promoted and subshells becoming degenerate

Degenerate Subshells

subshells that are equal in E (e.g. the 5 d subshells)

There are some atoms in cpds that don’t need to hybridize (bc they already have enough valence e-’s) but do. Why is this?

to allow for larger angles between the subshells and ∴ less repulsion ∴ a more stable molecule

When hybridization occurs, it is based on the __ __.

e- domain geometry

Co-ordinate Covalent Bonding

covalent bond in which both bonding e- come from the same atom

Co-ordinate Covalent Bonding is also called

DATIVE bonding

a) Draw the VSEPR for methane, CH4

b) Draw the VBD for methane, CH4

solution in notebook

a) Draw the VBD for CH2BrI

b) Identify i) the hybridization of the central atom and ii) the bond types

solution in notebook

e-’s in hybridized orbitals always form _ bonds

σ

unhybridized e- in the remaining parts of a multiple bond form _ bonds

π

Draw the VBD for CH2CHBr

solution in notebook

Draw the VBD for CHCBr

solution in notebook

Particles Present in Ionic Crystal

ions (cations + anions)

Particles Present in Metallic Crystal

cations

Particles Present in Molecular Crystal

molecules

Particles Present in Covalent-Network Crystal

atoms

Type of Force/Bond Between Particles in Ionic Crystal

ionic

• ions held together by electrostatic attraction

Type of Force/Bond Between Particles in Metallic Crystal

metallic

• sea of e-’s acts as “glue” for the fixed, +ve nuclei

Type of Force/Bond Between Particles in Molecular Crystal

IFs

• dipole-dipole, London dispersion, Hydrogen bonding

Type of Force/Bond Between Particles in Covalent-Network Crystal

covalent

• covalent bonds form between atoms

Properties of Ionic Crystals

• hard

• brittle

• high m/bp

• conductive in solution/liquid form

Properties of Metallic Crystals

• soft/hard

• low IE (conductive in solid/liquid form)

• ductile

• malleable

• lustrous

Properties of Molecular Crystals

• soft

• low m/bp

• non-conductive

Properties of Covalent-Network Crystals

• very hard

• brittle (don’t bend under pressure)

• high m/bp

• non-conductive

• insoluble

3 Van Der Waals Forces

• Hydrogen bonding

• dipole-dipole forces

• London dispersion forces

Hydrogen Bonding

occurs when H is attracted to O, F or N (have high EN → high difference in EN → stronger dipole-dipole forces)

(δ⁺ H of one molecule is attracted to δ^- O, F or N of another molecule)

Dipole-Dipole Forces

• δ⁺ and δ^- end of two molecules are attracted to each other

• only present in polar molecules

The strength of dipole-dipole forces are directly related to the ________ of the molecule, and inversely related to the ________ between the molecules.

polarity, distance

London Dispersion Forces

• instantaneous dipole created as e- move around an atom

• dipole creates other dipoles on other atoms

• atoms attract each other

• present in ALL molecules/atoms/ions

Intramolecular Forces vs Intermolecular Forces

intramolecular: forces between atoms within the same molecule/ion

intermolecular: forces between molecules/ions

Intermolecular forces are significantly _____ than covalent bonds.

weaker

All molecular forces are _____________.

electrostatic

VBT vs MOT

VBT:

• uses atomic orbitals to describe e- in atoms

MOT:

• uses molecular orbitals to describe e- in molecules

Atomic Orbitals vs Molecular Orbitals

a.o:

• applies to single atoms

m.o:

• applies to an entire molecule

Contour Representation

hybrid lobes

The total # of m.o. must be the ____ as the total # of a.o.

same

When 2 a.o. overlap, _ m.o. form.

2

What happens when two a.o. form two m.o.?

one m.o. results from constructive combination (bonding orbital)

the other m.o. results from destructive combination (anti-bonding orbital)

Constructive Combination

E is lower than the E of the orbitals from which it was formed (more stable)

e- density concentrated between nuclei

attraction of e- to both nuclei → lower E → bonding is favourable

Destructive Combination

E is greater than the E of the orbitals from which it was formed (less stable)

nodal region between nuclei (little e- density)

e- are repelled from bonding region → high e- density of opposite side of nuclei → higher E

bonding is unfavourable

Nodal Region

region of no e- density

Bonding Orbital

results from constructive combination

Anti-Bonding Orbital

results from destructive combination

The instability of a destructive M.O. is _______ than the stability of a constructive M.O. (the E difference is _______ in destructive M.O.)

greater

If there are 2 e- in the σ_1s and 2 e- in the σ^*_1s orbital, is the molecule stable?

no, because even though both have the same amount of e-’s (you’d expect them to cancel out), the E difference of the destructive M.O. is greater, so the molecule is higher E (∴ unstable)

Bond Order Formula

# of bonding e^- - # of anti-bonding e^- / 2

Homonuclear

2 of the same (atom)

What does a bond order of 1 mean?

single bond

The ______ the bond order, the ____ stable a molecule is.

higher, more

As overlap of orbitals increases, the E of the bonding MO is _______ and the E of the anti-bonding MO is ______.

lowered, raised