Week 1 - Bonding and Reactions Flashcards
What are intermolecular bonds
electrostatic forces between molecules
What are the 3 types of intermolecular forces
- dispersion
- dipole dipole
- hydrogen bonds
What are dispersion forces
Dispersion force are temporary dipoles forming between molecules, causing an electrostatic attraction for a brief period of time. e.g. N2
What are dipole dipole forces
A permanent dipole in a molecule - resulting in attractive and repulsive interactions e.g. HCl
What are h-bonds
A special dipole-dipole force involving a molecule with O,N or F lone pairs which will then be attracted to another N or O e.g. H2O
H bonds / H FONs
What is electronegativity
ability of an atom to attract shared e- in a covalent bond
How do you determine if a molecule is polar or not
*You can determine if a molecule is polar if you sum the dipole vectors and if there isn’t a net sum of zero then the molecule is polar
What is the general rule for solubility
like dissolves like
What are the 3 chemical reaction used in dental materials
- metathesis
- Photochemical reactions
- Redox reactions
What are metathesis (exchange reactions)
where there is no change in oxidation number, meaning no transfer of electrons
What are the driving forces for metathesis reactions (3)
- formation of a precipitate
- formation of a gas (less important)
- formation of a weak electrolyte
What are photochemical reactions
- e.g. light cure reactions
- Involves the absorption by the reactant of light as a photon - usually in the UV visible
- temperature generally has little effect on the overall rate of reaction,
- where the photon hits is important because photochemical reactions are regiospecific - meaning that photons activate parts of a molecule
How does the overall photochemical reaction occur
First a primary reaction occurs - which proceeds due to the absorption of radiation. At this stage the photon activates the covalent bond and splits the molecule into radicals
Then the secondary reactions occur from the species that are formed in the primary stage
What are photoinitiators
Photoinitiators are molecules which are prone to absorb photons and form radicals which then allow subsequent secondary reactions to occur.
What is quantum yield
The quantum yield indicates the nature of the incoming photons and how successful they are with reacting with molecules. We require the quantum yield to be considerably bigger than one so that a chain reaction can be initiated to drive polymerisation.
What is the equation for quantum yield
