Chapter 3 - Ionic Compounds Flashcards
List some properties of ionic compounds
- high melting and boiling points
- all solids at room temp.
- are made up of hard crystals
- neither malleable, or ductile, but brittle
- in solid state are non conductors of electricity
- good conductors of electricity in liquid state
- solutions formed from soluble ionic compounds are good conductors of electricity
- solubilities vary
- ionic substances formed from group 1&2 metals are white or colourless while transition metals form usually coloured substances
What are ionic compounds?
Compounds that are composed of positively charged and negatively charged ions.
Explain structure of ionic compound
The positive and negative ions in these ionic compounds are arranged in an orderly three-dimensional lattice. The position of the ions are fixed and apart from vibration about these fixed positions on other movement of the ions occurs in the solid compound.
Explain ionic bonding
Each ion in an ionic solid is held in the crystal lattice by strong electrostatic attractions to the oppositely charged ions around it. These electrostatic attractive forces between the positive and negative ions are called ionic bonds. A considerable amount of energy is required to disrupt these attractive forces between the positive and negative ions, ionic bonding is regarded as strong bonding.
Explain hardness and brittleness of ionic compounds
The strong, electrostatic attractions between the oppositely charged ions in the three-dimensional lattice result in ionic solids being hard and difficult to cut. The brittleness results from the orderly arrangement of ions in a crystal being disrupted after a layer of ions is forced to slide past another layer. Because of the displacement, ions of similar charge are forced closer to one another, with an increase in repulsive forces and a decease in attractive forces; as such the crystal will shatter.
Explain high melting points in ionic compounds
The forces between the oppositely charged ions in ionic compounds are so strong that large quantities of heat energy must be supplied to disrupt the crystal lattice and separate the ions. As such, ionic solids have high melting points.
Explain high boiling points in ionic compounds
In the liquid state, the ions have sufficient energy to move around randomly, but they are still close together. As a result, the attractive forces between the positive and negative ions in the liquid state are still strong. These attractive forces will be broken when the ionic compound boils to form a gas. Molten ionic compounds have high boiling points even though many decompose before they reach their boiling temps.
Explain solubility in ionic compounds
When a soluble ionic compound is added to water, the ions break away from the ionic lattice and mix with the water molecules.
If an insoluble ionic compound is added to water, the ions essentially remain bonded together in the ionic lattice.
Explain electrical conductivity in ionic compounds
Ionic solids do not conduct electricity because, although they contain charged particles, these ions occupy fixed positions and are not free to move through the solid lattice. Molten ionic compounds do conduct electricity because in the molten state the positive and negative ions are no longer strongly bonded in fixed positions in a lattice but are able to move through the liquid. Molten ionic compounds don’t conduct as strongly as metals, suggesting that ions in metals are much more mobile than ions in the molten state. They also conduct in water.
What are monatomic positive ions?
They have been formed when atoms have lost electrons. They are named after the element from which they were derived, for example Ba+2 is called barium ion and Ag+2 is called silver ion. Most positive ions are formed from metallic elements.
What is a polyatomic ion?
Ions that are made up of two or more atoms strongly bonded to one another. An example is ammonium, NH4+.
Explain monatomic negative ions
They are named by adding the suffix ‘-ide’ to the stem of the elements name.
If negative polyatomic ions contain oxygen the name often ends with ‘-ite’ or ‘-ate’.
If there are two ions composed of the same element together with oxygen, the name if the ion with the smaller number of oxygen atoms usually ends with ite and the larger number ends in ate; nitrite (NO2) and nitrate (NO3)
