Week 1: Overview of Food Chemistry
Atomic Chemistry
Atoms, Ions and Molecules
Mole Concept
Molarity And Dilution
Intermolecular Forces
Molecule: smallest particle of a substance that retains the chemical and physical properties of the substance and is composed of two or more atoms.
Ion: formed when an atom loses or gains electron(s).
A positive ion (cation) is formed when an atom loses electron(s).
A negative ion (anion) is formed when an atom gains electron(s).
Anion ( - ion ): Np+ < Ne-
Cation ( + ion ) : Np+ > Ne-
Most substances exist in molecular form, eg. CH4. Some metals exist in atomic form, eg., Fe, Zn.
L = 6.023 x 10^23 mol-1
Mole : amount of substance that contains the Avogadro constant of its building units (may be atoms, molecules, ions, electrons)
Molarity (a concentration): No. of moles of a substance dissolved in one litre of solution
, a set unit
Concentration can have a wide range of units
mol/L
g/L
g/mL
No. of mols of substance remains the same, but volume of solution is changed by adding more solvent
Dilution = Molarity / Concentration ↓
Two types of intermolecular bonding:
- Van der Waals forces
- Hydrogen bonding: Interaction between a hydrogen atom bonded to O, N, or F and O, N or F on another molecule
Permanent dipole-dipole interaction
Occurs when molecules have fixed dipole moments, eg. HCl
Effects of IMF
In solid state:
Molecules are tightly packed – held together by intermolecular forces, for eg, Van der Waals forces
In liquid state:
Molecules are further apart compared to solid state – energy is required to pull molecules apart
In gaseous state:
Molecules are further apart compared to the liquid state – more energy is required to pull molecules apart
DNA double helix – hydrogen bonding of base pairs
Tertiary structure of proteins – Van der Waals forces and hydrogen bonding
Affects the physical and chemical properties of food:
Cooking/heat denatures proteins in egg whites – disruption of hydrogen bonds
Drying of food takes a long time due to hydrogen bonding (in water)