PROPERTIES OF IONIC COMPOUNDS Excerpt from chemistry.about.com Here are the properties shared by the ionic compounds. Notice that the properties of ionic compounds relate to how strongly the positive and negative ions attract each other in an ionic bond. Ionic compounds form crystals. Ionic compounds form crystal lattices rather than amorphous solids. Ionic bonds form when a metal reacts with a non-metal. Metals form positive ions; non-metals form negative ions. The oppositely charged ions are arranged in a regular way to form giant ionic lattices [lattice: A lattice is a regular grid-like arrangement of atoms in a material. ]. Ionic compounds often form crystals as a result. The illustration above shows part of a sodium chloride (NaCl) ionic lattice. Ionic compounds have high melting points and high boiling points. High temperatures are required to overcome the attraction between the positive and negative ions in ionic compounds. Therefore, a lot of energy is required to melt ionic compounds or cause them to boil.
Ionic compounds are hard and brittle. Ionic crystals are hard because the positive and negative ions are strongly attracted to each other and difficult to separate, however, when pressure is applied to an ionic crystal then ions of like charge may be forced closer to each other. The electrostatic repulsion can be enough to split the crystal, which is why ionic solids also are brittle. Ionic compounds conduct electricity when they are dissolved in water. When ionic compounds are dissolved in water the dissociated ions are free to conduct electric charge through the solution. Molten ionic compounds (molten salts) also conduct electricity. Ionic solids are good insulators. Although they conduct in molten form or in aqueous solution, ionic solids do not conduct electricity very well because the ions are bound so tightly to each other. Here are examples of ionic bonds and ionic compounds: NaBr - sodium bromide KBr - potassium bromide NaCl - sodium chloride NaF - sodium fluoride KI - potassium iodide KCl - potassium chloride CaCl 2 - calcium chloride K 2 O - potassium oxide MgO - magnesium oxide You can recognize ionic compounds because they consist of a metal bonded to a nonmetal.
Lab PROCEDURE: 1. Use the information above to fill out the first row of the chart below. 2. Measure 0.5 grams of Salt on a scrap paper. 3. Fill the beaker about 1/2 full of water. Add the compound, stir, and set aside. 4. Measure another 0.5 grams of salt and heat the compound on a scoopula. Gently heat the compound over a Bunsen burner flame and observe if it melts. If it does, write low under MELTING POINT in your data chart. If it does not, write high. 5. Clean the scoopula thoroughly. 6. Return to your beaker. Observe: has compound dissolved in the water? If it did, write yes under SOLUBILITY in your data chart. If it did not, write no. 7. Test your solution/mixture with the light bulb conductivity tester (as shown on the right). Carefully hold the beaker so the probes are in contact with the mixture. Observe whether or not the bulb lights up. If it does, write yes under CONDUCTIVITY in your data chart. If it does not, write no. 8. Rinse out the beaker thoroughly and repeat steps 1 7 for each of the other compounds. Compound IONIC Salt Prediction Solubility in Ionic or H2O Covalent? Yes or No Electrical Melting Other Conductivity Point observations Yes or No and High or Low (or pictures) measurement
PROPERTIES OF COVALENT COMPOUNDS Excerpt from chemistry.about.com These are properties of covalent compounds, also known as molecular compounds. Covalent compounds are a diverse group of molecules, so there are several exceptions to each 'rule'. When looking at a compound and trying to determine whether it is an ionic compound or a covalent compound, it's best to examine several properties of the sample. Most covalent compounds have relatively low melting points and boiling points. While the ions in an ionic compound are strongly attracted to each other, covalent bonds create molecules that can separate from each other when a lower amount of energy is added to them. Therefore, molecular compounds usually have low melting and boiling points. Covalent compounds tend to be soft and relatively flexible. This is largely because covalent bonds are relatively flexible and easy to break. The covalent bonds in molecular compounds cause these compounds to take form as gases, liquids and soft solids. As with many properties, there are exceptions, primarily when molecular compounds assume crystalline forms. Covalent compounds tend to be more flammable than ionic compounds. Many flammable substances contain hydrogen and carbon atoms which can undergo combustion, a reaction that releases energy when the compound reacts with oxygen to produce carbon dioxide and water. Carbon and hydrogen have comparable electronegativies so they are found together in many molecular compounds. When dissolved in water, covalent compounds don't conduct electricity. Ions are needed to conduct electricity in an aqueous solution. Molecular compounds dissolve into molecules rather than dissociate into ions, so they typically do not conduct electricity very well when dissolved in water. Many covalent compounds don't dissolve well in water. There are many exceptions to this rule, just as there are many salts (ionic compounds) that don't dissolve well in water. However, many covalent
compounds are polar molecules that do dissolve well in a polar solvent, such as water. Examples of molecular compounds that dissolve well in water are sugar and ethanol. Examples of molecular compounds that don't dissolve well in water are oil and polymerized plastic. 1. Use the information above to fill out the first row of the chart below. 2. Conduct the same experiments for sugar. Compound Prediction Ionic or Covalent? Solubility in H2O Yes or No Electrical Conductivity Yes or No and measurement Melting Point High or Low Other observations (or pictures) COVALENT Sugar
OTHER COMPOUNDS: Compound Prediction Ionic or Covalent? Solubility in H2O Yes or No Electrical Conductivity Yes or No and measurement Melting Point High or Low Other Observations or pictures Ionic Covalent 1. Gelatin 2. Sugar 3. Salt 4. Baking Soda 5. Limestone 6. Rock Salt 7. Cornstarch 8. Calcium Chloride