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.

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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 ↓

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Two types of intermolecular bonding:

  1. Van der Waals forces
  1. 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)