ionic compounds

what are ionic compounds

All compounds form when atoms of different elements share or transfer electrons. Compounds in which electrons are transferred from one atom to another are called ionic compounds. In this type of compound, electrons actually move between the atoms, rather than being shared between them. When atoms give up or accept electrons in this way, they become charged particles called ions. The ions are held together by ionic bonds, which form an ionic compound. Ionic compounds generally form between elements that are metals and elements that are nonmetals. For example, the metal calcium (Ca) and the nonmetal chlorine (Cl) form the ionic compound calcium chloride (CaCl2 ). In this compound, there are two negative chloride ions for each positive calcium ion. Because the positive and negative charges cancel out, an ionic compound is neutral in charge. Q: Now can you explain why calcium chloride prevents ice from forming on a snowy road? A: If calcium chloride dissolves in water, it breaks down into its ions (Ca2+ and Cl ). When water has ions dissolved in it, it has a lower freezing point. Pure water freezes at 0 C. With calcium and chloride ions dissolved in it, it wont freeze unless the temperature reaches -29 C or lower.

crystals

Many compounds form molecules, but ionic compounds form crystals instead. A crystal consists of many alternating positive and negative ions bonded together in a matrix. Look at the crystal of sodium chloride (NaCl) in the Figure bonds. Sodium chloride crystals are cubic in shape. Other ionic compounds may have crystals with different shapes.

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naming ionic compounds

Ionic compounds are named for their positive and negative ions. The name of the positive ion always comes first, followed by the name of the negative ion. For example, positive sodium ions and negative chloride ions form the compound named sodium chloride. Similarly, positive calcium ions and negative chloride ions form the compound named calcium chloride. Q: What is the name of the ionic compound that is composed of positive barium ions and negative iodide ions? A: The compound is named barium iodide.

properties of ionic compounds

The crystal structure of ionic compounds is strong and rigid. It takes a lot of energy to break all those ionic bonds. As a result, ionic compounds are solids with high melting and boiling points. You can see the melting and boiling points of several different ionic compounds in the Table 1.1. To appreciate how high they are, consider that the melting and boiling points of water, which is not an ionic compound, are 0 C and 100 C, respectively. Ionic Compound Sodium chloride (NaCl) Calcium chloride (CaCl2 ) Barium oxide (BaO) Iron bromide (FeBr3 ) Melting Point ( C) 801 772 1923 684 Boiling Point ( C) 1413 1935 2000 934 Solid ionic compounds are poor conductors of electricity. The strong bonds between their oppositely charged ions lock them into place in the crystal. Therefore, the charged particles cannot move freely and carry electric current, which is a flow of charge. But all that changes when ionic compounds dissolve in water. When they dissolve, they separate into individual ions. The ions can move freely, so they can carry current. Dissolved ionic compounds are called electrolytes. The rigid crystals of ionic compounds are brittle. They are more likely to break than bend when struck. As a result, ionic crystals tend to shatter easily. Try striking salt crystals with a hammer and youll find that they readily break into smaller pieces. Click image to the left or use the URL below. URL:

uses of ionic compounds

Ionic compounds have many uses. Some are shown in the Figure 1.2. Many ionic compounds are used in industry. The human body needs several ions for good health. Having low levels of the ions can endanger important functions such as heartbeat. Solutions of ionic compounds can be used to restore the ions.

instructional diagrams

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questions

ionic compounds form when ions of two different elements share electrons.

a. true

-->  b. false

an ionic compound is always neutral in charge.

-->  a. true

b. false

how are ionic compounds named?

-->  a) the positive ion comes first in the compound name.

b) the negative ion comes first in the compound name.

c) the ion in the higher-numbered period comes first in the compound name.

d) two of the above

properties of ionic compounds include

a) high melting point.

b) ability to conduct electricity.

c) brittleness.

-->  d) two of the above

uses of ionic compounds include

a) making fireworks.

b) detecting moisture.

c) melting ice.

-->  d) all of the above

diagram questions

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