03 + 08 Chemical Bonding I + II Flashcards
Ionic Lattice
Structure
- ions held in fixed positions in an orderly arrangement
- attraction between the oppositely-charged ions is a maximum
- repulsion between similarly-charged ions is a minimum
- bonds are non-directional i.e. attracts an oppositely-charged ion in all directions without a preferred orientation
Ionic Bond, IB
Definition
An electrostatic attraction between cations and anions i.e oppositely-charged ions.
IBs are non-directional
Lattice Energy, ΔHlatt/ LE
Formula
|LE| = |q+ x q-/ r+ + r-|
where,
q+ = charge on cation
q- = charge on anion
r+ = radius of cation
r- = radius of anion
↑|LE|, ↑ strength of IB
Ionic Bond
Factor(s)
- Higher Charge: ↑ Electrostatic Attraction
- Smaller Radius: ↓ Inter-ionic Distance
Ionic Compounds
Physical Properties
- High melting & boiling point
a. ↑ amounts of energy required to break the bonds between oppositely-charged ions for melting/ boiling - Generally soluble in polar solvents eg. H2O and vice versa
- Conducts electricity in (ℓ) & (aq) states
a. Ions are mobile and can act as mobile charge carriers - Hard & brittle
a. Slight displacement along a cleavage planes brings ions of like charges opposite each other
b. Strong attraction between the planes becomes strong repulsion
c. Plane shatters
Giant Molecular Lattice
Structure & Properties of Diamond
- High melting point & insolubility in H2O/ other solvents
a. sp3-hybridised C
b. Covalently bond to 4 other C atoms
c. Tetrahedral arrangement
d. Strong and rigid structure - Electrical insulator
a. Made up of neutral atoms
b. Lack of mobile charge carries i.e delocalised e-
Giant Molecular Lattice
Structure & Properties of Graphite
- Layer structure & planes of interconnected hexagonal rings of C
a. sp2-hybridised C
b. Forms 3 σ bonds with 3 other C atoms
c. Trigonal planar shape about C
d. BA of 120° - Electrical conductor
a. Unhybridised p-orbital, containing single e-
b. Continuous overlap with p-orbital of immediate neighbours
c. Extended π-e- cloud
d. Delocalisation of π e- over whole layer
e. Electricity conducted parallel to the layers - High melting point: Used as crucibles for molten metals and reentry nose cones of rockets
a. Strong covalent bonds within each layer
b. ↑ energy is required to overcome strong forces of attraction - Soft: Used in pencils and lubricants
a. Weak id-id interactions between each layer
b. Layers glide over each other
Giant Molecular Lattice
Structure & Properties of Silicon Dioxide, Quartz
- Hard & insoluble in all solvents
a. Covalent bonds between Si & 4 O/ O & 2 Si
b. Tetrahedral arrangement
c. Rigid 3D structure due to strong covalent bonds - Electrical insulator
a. Made of atoms
b. Lack of mobile charge carriers i.e delocalised e-
Simple Molecular Lattice
Structure & Properties
- Low melting point
a. Attract each other through weak id-id interactions - Soluble in non-polar solvents
a. Solute and solvent have the same type of intermolecular interactions, id-id interactions - Electrical insulator unless ionisation in (aq) occurs
a. Lack of mobile charge carriers
Metallic Lattice
Structure
- Rigid lattice of cations
- ‘Sea’ of delocalised e- = displaced valence e-
e- belong to the crystal lattice as a whole instead of a particular cation
Metallic Bond, MB
Definition
The electrostatic attraction between a lattice of cations and delocalised electrons.
MBs are non-directional
Metallic Bonds, MB
Factor(s)
- Number of VE available
a. ↑ VE
b. ↑ strength of MB - Charge of cation
a. ↑ charge
b. ↑ strength of MB - Size of cation
a. ↓ size
b. ↑ charge density
c. ↑ electrostatic attraction for the delocalised e-
d. ↑ strength of MB
Metals
Physical Properties
- High electrical conductivity in all states
a. Presence of mobile charge carries i.e delocalised e-
b. Flow toward the positive terminal as long as potential difference is applied to the end of a metal - Good thermal conductivity
a. e- take in thermal energy
b. e- move faster and more randomly
c. collide with other e-
d. energy is passed along - Malleable i.e beaten into shape & ductile i.e drawn into a wire
a. Cations can glide over another easily without breaking the MB - High density
a. Cations are closely-packed - High melting & boiling points
a. Strong MB
Drawing dot-and-cross
Polyatomic Ions
For cations:
Assign charge to less electronegative atoms
For anions:
Assign charge to more electronegative atoms
Covalent Bond
Definition
The electrostatic attraction between the shared pair of electrons and the positively-charged nuclei.
Dative Covalent Bond
aka Co-ordinate Bond
Shared pair of electrons is provided by only one of the bonding atoms.
Representation: → from the donor atom to acceptor atom
Dative Covalent Bond
Conditions
aka Co-ordinate Bond
Donor atom: Lone pair of e-
Acceptor atom: Vacant, low-lying orbital
Low-lying orbital must be in the same sub-shell or ES as those occupied
Drawing dot-and-cross
Covalent Compounds
- Determine the number of VE of each other.
- Identify the central atom which is normally the least EN atom.
- Arrange the peripheral atoms.
- Determine the bonds between the central and peripheral atoms in order to achieve duplet/ octet structure where possible.
- Check that e- on every atom correspond to group number.
- Draw any remaining e- as lone pairs.
For elements in Period 3 and beyond, molecules can have an expanded octet.
VSEPR Theory
Basis
- e- pairs around the central atom of a molecule are arranged as far apart as possible in space, minimising mutual repulsion.
- LP-LP repulsion > LP-Bond Pair > BP-BP repulsion
VSEPR Theory
2 Electron Density Regions
Electron-Pair Geometry, EPG : Linear
O Lone Pairs, LP;
Shape: Linear
Bond Angle, BA: 180°
For LP, -2°
VSEPR Theory
3 Electron Density Regions
EPG : Trigonal Planar
O LP:
Shape: Trigonal Planar
BA: 120°
1 LP:
Shape: Bent
BA: <120°
For LP, -2°
VSEPR Theory
4 Electron Density Regions
EPG: Tetrahedral
0 LP:
Shape: Tetrahedral
BA: 109.5°
1 LP:
Shape: Trigonal Pyramidal
BA: ~107°
2 LP:
Shape: Bent
BA: ~105°
For LP, -2°
VSEPR Theory
5 Electron Density Regions
EPG: Trigonal Bipyramidal
0 LP:
Shape: Trigonal Bipyramidal
BA: 90°/ 120°
1 LP:
Shape: See-saw
BA: N.A.
2 LP:
Shape: T-shape
BA: 90°
3 LP:
Shape: Linear
BA: 180°
For LP, -2°
VSEPR Theory
6 Electron Density Regions
EPG: Octahedral
0 LP:
Shape: Octahedral
BA: 90°
1 LP:
Shape: Square Bipyramidal
BA: < 90°
2 LP:
Shape: Square Planar
BA: 90°
For LP, -2°
VSEPR Theory
Bond Angle Modification
- e- pair-e- pair repulsion
a. Closer e--pair is to the central atom, ↑ repulsion
b. About the same central atom, LP exerts ↑ repulsion than BP as LP is attracted to 1 nucleus and is closer to the central atoms while BP is attracted to 2 nuclei.
c. As no. of LP ↑, BA deviates ↑ greatly from the predicted angle. - Effect of EN of central atom on BA
a. ↑ EN the central atom
b. BPs are drawn closer to itself
c. BP e- are nearer to the nucleus
d. ↑ repulsion is exerted
e. BA ↑
Instantaneous dipole-induced dipole, id-id, interactions
Formation & Factor(s)
Formation:
1. e- density of a particle can be asymmetrical
2. Instantaneous dipole formed
3. Dipole induced in neighbouring particle
4. Attraction occurs
Factor(s):
1. Electron Cloud Size = Mr
a. ↑ e- cloud
b. ↑ easily polarised
c. ↑ ease of formation of id-id interactions
d. ↑ strength of id-id interactions
2. Surface area for molecular interaction eg. branched HC vs straight-chain HC
a. ↓ branching
b. ↑ surface area for intermolecular interactions
c. ↑ strength of id-id interactions
d. straight-chain molecules have a ↑ boiling point than branched isomers
Use the donut vs. baguette analogy for point 2
Permanent dipole-permanent dipole, pd-pd interactions
Factor(s)
Polarity of the molecule
Permanent dipole-permanent dipole, pd-pd interactions
Formation & Criteria of Hydrogen Bond
Formation:
1. > EN F/ O/ N atom causes H to have a ↑ δ+ charge.
2. ↑ δ+ H forms strong attraction with LP of e- on adjacent molecule, forming the H Bond.
Criteria:
1. H atom is bonded to F/ O /N atom.
2. LP of e- on F/O/N atom in a neighbouring molecule bearing δ- to attract δ+ of H atom.
H Bond can occur between the same, different types of molecules or within a molecule.
H Bond
Effect on Physical Properties
- Extensiveness of H Bonding
- Strength of H Bond
