Ionic Compounds - Properties Overview

Today we looked at the characteristic properties of ionic compounds:

• high/very high melting and boiling points
• electrical insulators as solids
• electrical conductors as liquids and solutions
• hard and brittle
• only soluble in polar solvents

We had to use our understanding of their structure (a lattice of cations and anions) and bonding (directional electrostatic attractions called ionic bonds) to explain each of these properties.

Ionic Compounds - Solubility

This is the hardest property to explain, especially for ionic compounds. The strength of the ionic bond suggests that ionic compounds should not dissolve at all. However, we know that salt (sodium chloride) dissolves in water. Why?

Water is a polar solvent. One side (pole) of water has a small positive charge. The other pole has a slight negative charge. The negative pole of multiple water molecules can be attracted to a cation, so surrounding it. The pull they have on the cation overcomes the ionic bond, so the cation dissolves.

At the same time, the same thing would happen with the positive pole of other water molecules being attracted to (and surrounding) an anion, so dissolving the anion.

Ionic Compounds - Melting Point

We need to use the structure and bonding of ionic compounds to justify their very high melting points.

Types of Substances

In this topic, we will be relating the properties of substances (particularly in their solid form) to their structure and bonding (particles and bond types). Today was an overview of these types of substances, to give us the "big picture:.

We will start by learning about ionic compounds from Monday.

Ion Formation

We can use our understanding of the Periodic Table to infer the charge of monatomic ions (made up of only one atom):

The Periodic Table

Today we started by looking at some data about 20 elements, and trying to organise them by common properties and trends. These common properties help us understand the structure of the Periodic Table of Elements, and to use it to make predictions. We had nine unknown elements that we needed to predict the position of in our Periodic Table.

We then learned that the Periodic Table is organised into columns (Groups/Families) of elements with similar chemical properties. The rows (Periods) are elements all with the same number of electron shells ("energy levels"). For example, all elements in the second period have two electron shells, and their valence electrons are in the second electron shell.