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Chemistry

This section below covers the following two properties of substances:

  1. Chemical properties
  2. Physical properties

Chemical Properties

Chemical property of substances illustrates their ability to undergo chemical change. When a substance undergoes a chemical change, its chemical composition changes, and elements in the original substance are rearranged into a new compound or element. Following are some of the examples of chemical properties of substances

  • Flammability 
  • Toxicity
  • Acidity
  • Reactivity
  • Heat of combustion 

Following are some of the chemical changes that can be found in everyday life:

  • Baking a cake
  • Milk going sour
  • Burning of a paper
  • Rusting of iron

Physical properties

Physical properties describe a physical system of a substance that can be measured without changing the chemical composition. There are two types of physical properties:

  1. Intensive properties: This type of property stays the same no matter the amount of matter. Examples include color, density, and conductivity.
  2. Extensive properties: This type of property changes with the amount of matter available. Examples include mass, volume, and length. 

When a physical change occurs, it does not change the molecular composition of matter. For example when water freezes to become ice the physical appearance changes but the chemical composition does not change. The still contains water molecules just like how the liquid contains water molecules before it freezes. 

Intermolecular and intramolecular forces

Intramolecular forces: As the name states it describes the force inside the molecule. It is the force that holds the atoms together in a molecule. 

Intermolecular forces: These are the forces that exist between molecules.

For example, water is made up of many molecules. The force that keeps these individual water molecules is known as an intermolecular force. The force that holds the hydrogen and oxygen atoms together to form a single water molecule is called the intramolecular force. 

The figure below illustrates the intermolecular and intramolecular forces

The phase of a substance and boiling point are determined by the strength of intermolecular force present and the kinetic energy of molecules. 

There are four different types of intermolecular forces:

  • Ionic forces
  • Hydrogen bonding
  • Van Der Waals Dipole-Dipole Interactions
  • London dispersion forces

Ionic forces

The attraction between positively charged ions (cations) and negatively charged ions (anions) is known as ionic force. These are the strongest bonds of all types. The figure below illustrates the ionic force that exists in NaCl.

Hydrogen bonding

Hydrogen bonding occurs in covalently bonded molecules that where hydrogen is bonded with one of the highly electronegative elements such as Fluorine, Oxygen, or Nitrogen.

The figure below illustrates the hydrogen bonding that exists between water molecules

 

Van Der Waals Dipole-Dipole Interactions

This occurs between covalently bonded dipole molecule that does not involve hydrogen. 

London dispersion forces 

This occurs between molecules due to the instantaneous dipole that forms within molecules because of electron movement. 

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