Chemical Bonding and Structure

What is an ionic bond?

The electrostatic attraction between oppositely charged ions

What is a covalent bond?

The electrostatic attraction between nuclei and shared pairs of electrons

What is electronegativity?

A measure of the ability to attract a shared pair of electrons in a covalent bond

What is a dative covalent bond?

A covalent bond in which both electrons are donated from the same atom

Explain the structure of diamond

every C atom bonded in a tetrahedral lattice with 4 other C atoms;

very strong/hard

Explain the structure of graphite

Every C atoms bonded with 3 others in a trigonal planar shape;

Layers of carbon hexagons are held together by London dispersion forces;

mobile electrons between layers allow conductivity of electricity;

layers can slide off

Explain the structure of graphene

a single layer of graphite;

very strong;

conducts electricity

Explain the structure of buckminsterfullerene (C60)

Every C atom bonded with 3 others (double and single bonds):

interlocking penta- and hexagons;

like a football

Explain the structure of silicon dioxide (SO2)

also called quartz

Allotropes...

vary in both chemical and physical properties

What is a resonance structure?

multiple possible arrangements for a double bond in a molecule;

Linear shape

180°;

2 e- domains;

0 lone pairs

Trigonal planar shape

120°;

3 e- domains;

0 lone pairs

Bent shape (SO2)

~118°;

3 e- domains;

1 lone pair

Tetrahedral shape

109.5°;

4 e- domains;

0 lone pairs

Trigonal pyramidal shape

107°;

4 e- domains;

1 lone pair

Bent shape (H2O)

104.3°;

4 e- domains;

2 lone pairs

VSEPR theory

Valence Shell Electron Repulsion Theory;

e- domains spread as far apart as possible in 3D space

London dispersion forces/ instantaneous-induced dipole forces

attraction between molecules due to random temporary dipoles;

weakest

Dipole-dipole forces

attractions between molecules with permanent dipoles;

middle

Hydrogen Bonds

attractions between lone pairs of e- and H atoms attached to F, O or N

What is a metallic bond?

The electrostatic attractions between nuclei and delocalised electrons

What is an alloy?

A different metal ion being introduced into the metallic lattice;

alter properties: may increase conductivity, resistance to corrosion or lower the melting point

Properties of metals/alloys

mallable (hammered into shape);

ductile (drawn into wires);

conduct electricity due to delocalised electrons;

layers of ions may slide over each other

Trigonal bipyramidal shape

90°, 120°, 180°;

5 e- domains;

0 lone pairs

Seesaw shape

~90°, ~120°, ~180°;

5 e- domains;

1 lone pair

T-shaped

~90°, ~180°;

5 e- domains;

2 lone pairs;

Linear (XeF2)

180°;

5 e- domains;

3 lone pairs

Octahedral shape

90°, 180°;

6 e- domains;

0 lone pairs

Square pyramidal shape

~90°, ~180°;

6 e- domains;

1 lone pair

Square planar shape

90°, 180°;

6 e- domains;

2 lone pairs

Formal Charge equation

FC = V - 1/2B - N;

ΔFC closest to 0 = preferred structure;

if same formal charges - lower FC on most e-negative atom = most stable

Sigma bond

end-to-end overlap of atomic orbitals (between s&s or s&p)

Pi bond

side-to-side overlap of p orbitals

single bond (in terms of σ and π)

only σ

double bond (in terms of σ and π)

1σ & 1π

triple bond (in terms of σ and π)

1σ & 2π

resonance

only present if e- can move within the molecule (more than one way of positioning double bonds in Lewis structures:

delocalisation of π bonds across a molecule (delocalisation of π e- = conjugation)

Evidence for resonance

bond lengths will be in-between bond lengths seen in resonance forms