Properties of Ionic and Molecular Compounds

Did you know that it is not water that is responsible for conducting electricity but the substances that are dissolved in it?


B7.2 Hair dryer in a bathtub
Recall that ionic compounds are composed of ions whereas molecular compounds are composed of individual molecules. It is the underlying structures of these compounds that give them their unique characteristics. Using these unique characteristics, you will be able to distinguish between samples of ionic compounds from samples of molecular compounds.

Here is a comparison of some of the key properties of ionic compounds and molecular compounds.

Ionic Molecular
  • solid at room temperature
  • high melting and boiling points
  • hard
  • brittle
  • conduct electricity when liquid or dissolved in water
  • a variety of colours
  • insulators when solid
  • solid, liquid, or gas at room temperature
  • relatively low melting and boiling points
  • softer
  • more flexible
  • do not conduct electricity when liquid or dissolved in water
  • mostly colourless or white
  • more flammable

  Digging Deeper

© Wikimedia Commons
B7.6 Neuron

Electrolytes are essential in the human body.  One process that they are required for is to help the transmittance of nerve signals.

The characteristic properties of ionic compounds are a result of the strong, rigid, directional bonds formed between cations and anions in the crystal lattice structure and the ability of the ions to separate into individual species when the substance melts or is dissolved in water.

  Watch This

Properties of Ionic Substances @ YouTube FuseSchool – Global Education  


Watch this video to see how ionic properties are related to the crystal lattice structure.

 

  Properties of Ionic and Molecular Compounds Continued


Let’s look more closely at why ionic compounds conduct electricity when they are melted or dissolved in water and why molecular compounds do not.

B7.3 Solution not conducting because there are just neutral water molecules
B7.4 Solution conducting because of free floating ions
B7.5 Solution not conducting because there are just neutral water molecules and other neutral molecules present
Water does not conduct because it does not contain charged particles. Ionic compounds dissociate (break apart into ions) when they dissolve in water. These charged particles (ions) provide a pathway to conduct electricity. Molecular compounds do not create ions in solution because the atoms of the molecules stay bonded together. When molecular compounds dissolve, they created neutral molecules, so there is no pathway for electricity to flow.

  Watch This

Molten Salt (NaCl) Conducts Electricity @ YouTube BerkeleyChemDemos 


Watch this video to see how conductivity is affected when table salt (sodium chloride) melts.