As we know, all matter is made up of little particles.
When a sample of material is known to use covalent bonds, the material is said to be “molecular,” or in other words, the material is made up of “molecules.” A cluster of HCl molecules is shown below. Molecules have an electrical charge of zero.
When a sample of matter is known to use ionic bonds, the material is said to be “ionic,” or in other words, the material is made up of “ions.” A cluster of Al3+ and O2- ions is shown below. Ions have electrical charges on them.
One way of knowing whether a material is using ionic or covalent bonds is to test its melting point. It is generally true that molecular substances have lower melting points than ionic substances. For example, HCl melts at -115oC while Al2O3 melts at 2072oC.
1. Decide whether you think the attraction between ions is stronger than between molecules, or visa-versa. Explain what evidence you are using from the information above, in order to make a conclusion about this.
2. When HCl molecules are melted, do we still have HCl molecules, or are the molecules broken down into H and Cl atoms? Explain based on your understanding of whether the process of melting is a physical or chemical change.
3. When ionic substances are melted, they can conduct electricity. When they are solids, they can not. Explain why this is so.
4. Molecular substances do not conduct electricity in either solid or liquid form. Why not?
ENRICHMENT: Research what a “polar” molecule is. Find out whether or not water molecules are polar. Draw a set of 4-5 water molecules showing how they arrange when touching each other.
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