Ionic compounds are pure substances formed when two or more ions are held next to each other by electrical attraction. Also, it is formed when a metal is in the presence of a non-metal. One of the ions has a positive charge, or cation, and the other has a negative charge, or anion. Cations are usually metal atoms and anions are either non-metals or polyatomic ions (ions with more than one atom). Ionic compounds are only solid at room temperatures. The main properties of ionic compounds are: all ionic compounds form crystals, it has a high boiling and melting point, it is hard and brittle, and it conducts electricity when it is dissolved in an aqueous solution. Crystals are formed because the negative and positive charges come together tightly, or stuck, and they stack into groups. Together, they form a distinct crystal shape. High melting and boiling points are major properties of ionic compounds. The temperatures are high because of the way the compound is held together. They are together as crystals and these big blocks of crystals are full of positive and negative charges all stuck together (Fig. 1). As a result, it takes a huge amount of energy to break it apart. Ionic compounds are hard and brittle also because of the way it's held together. Since they"re tightly packed, the charges can't and don't move, so they don't bend at all. It is also the reason why it is brittle. If I were to give a big crystal a strong force on it, the crystal would shatter because of the amount of energy used to break the crystal. Ionic compounds conduct electricity when dissolved in water because of the water molecules pulling the positive and negative ions apart from each other. Now, the ions are all scattered all over the place. Electricity is simply the movement of electrons through metals. Dissolved salts are the same way. When salt is dissolved in water, the positive and negative ions in the water allow electrons to flow better than if there was only water.
