Types of Solids

Types of Solids What are some common categories of solids, and their properties? Why? Not all solids are the same. Solid substances have a tremendously wide range of melting points. Helium melts at −272 °C while tantalum hafnium carbide melts at 4215 °C. Some are conductive, others are not. Some readily dissolve in water, others do not. In this activity, you’ll look at four types of solids, the types of substances that are typically in each category, and some of the properties typical for each. Ionic Solids Model 1 – Arrangements of Atoms in Solids Calcium Bromide (CaBr2) Sodium Chloride (NaCl) Nitrogen (N2) Ice (H2O) Dry Ice (CO2) Diamond (Carbon) Silica (SiO2) Silicon (Si) Platinum (Pt) Brass (Cu and Zn) Nickel (Ni) Metallic Solids Network Covalent Solids Molecular Solids Iron(II) Sulfide (FeS) 1. List the four types of solids illustrated in Model 1. ionic, molecular, network covalent , metallic 2. Complete columns A–C in the table below by referring to the examples in Model 1. Place a check in the box that appropriately describes the types of atoms that are usually seen in each type of solid. A B C D E Atoms are All atoms are All atoms metals and Molecular Formula nonmetals are metals nonmetals structure units F Attractive forces Ionic Solids ionic bonds Molecular Solids intermolecular forces Network Covalent Solids covalent bonds metallic bonds Metallic Solids 3. Complete columns D and E in the table above by referring to the examples in Model 1. Place an X in the box that appropriately describes the arrangement of atoms or molecules in the solid (either molecular—distinct molecules, or formula units—repeating units in three dimensions with no distinct molecules). 4. There are four possible forces of attraction that hold atoms or molecules together in a solid: covalent bonds, ionic bonds, metallic bonds and intermolecular forces. These depend on the type of atoms in the solid and whether the connections are between ions, atoms or molecules. Within your group, discuss the type of attractive forces that are most likely holding the atoms or molecules together in each type of solid. List your answers in column F in the table above. Read This! When a solid substance is heated, the weakest attractive forces in the solid structure are overcome, and the solid melts. In some cases, this results in individual atoms or ions, and in other cases, this results in individual molecules. Regardless, melting is a physical change and does not alter the chemical formula of the substance. 5. For each type of solid in Model 1, indicate the type of attractive forces that are broken upon melting, and describe the individual particles that make up the resulting liquid. Bonds/forces broken upon melting Individual particles in the liquid Ionic ionic bonds Molecular intermolecular forces covalent bonds molecules atoms metallic bonds metal atoms Network covalent Metallic cations+anions 6. Match the following descriptions with one of the four types of solids. Metallic atoms with very loose electrons for a lattice of nuclei held together by a sea of electrons, or metallic bonds. Nonmetal atoms form molecules with covalent bonds. The molecules molecular are held together in a solid by intermolecular forces of attraction. Metal and nonmetal atoms form a lattice of alternating positive and ionic negative ions held together by ionic bonds. network covalent Nonmetal atoms form a lattice structure held together with covalent bonds. metallic 7. If a particular solid had very strong attractive forces, would you expect the melting point of that solid to be relatively high or relatively low? Explain your reasoning. particles with strong attractive forces require lots of energy to break apart, resulting in a relatively high melting point Model 2 – Melting Points and Enthalpies of Fusion Type of Solid Ionic Molecular Network covalent Metallic Substance Chemical Formula Iron(II) sulfide Calcium bromide Sodium chloride Nitrogen Water Carbon dioxide Diamond Silica Silicon Platinum Brass Nickel FeS CaBr2 NaCl N2 H 2O CO2 C SiO2 Si Pt Cu and Zn Ni Melting Point Enthalpy of Fusion (°C) (kJ/mole) 1195 730 804 −210 0.0 −78 3550 1650 1687 1770 ∼930 1453 51.0 17.5 30.3 0.72 6.02 8.10 117.0 12.5 50.0 24.0 Varies 71.0 8. Notice that the substances listed in Model 2 are the same as those in Model 1. a. Which type of solid has the lowest melting points? molecular b. Is your answer in part a consistent with your answer to Question 7? yes 9. The enthalpy of fusion given in Model 2 for each substance is a measure of the energy (in kJ) needed to melt a mole of that substance. a. Which type of solid has the lowest enthalpies of fusion? molecular b. Is your answer in part a consistent with what you know to be the relative strength of the four types of attractive forces? Explain why or why not. yes, because it takes less energy to overcome weaker forces 10. Using both melting point data and enthalpy of fusion data, rank the remaining three types of solids from weakest attractive forces to strongest attractive forces. Make sure there is consensus in your group before moving on. ionic, metallic, network covalent Read This! As you may have found in answering the previous question, there is a lot of overlap in properties among the four types of solids. For example, platinum (a metallic solid) has a higher melting point than several of the network covalent solids, but the majority of metallic solids have a much lower melting point than network covalent solids. The categories for solids are not as clear cut as we would like them to be; nevertheless, they are useful for predicting relative properties. 11. Use the concepts you have learned in this activity to predict the type of solid for each of the following substances. Anyone in your group should be able to justify your group’s answers. Substance Chemical Formula Chlorine Cl2 Hydrogen bromide Titanium Melting Point Enthalpy of Fusion (°C) (kJ/mole) −102 6.41 HBr −87 2.41 Ti 1668 20.9 Sodium bromide NaBr 747 26.1 Boron B 2076 50.2 Mercury Hg −38.3 2.29 Type of Solid molecular molecular metallic ionic network covalent metallic Read This! Properties other than melting point and enthalpy of fusion can be helpful when categorizing a substance as one of the four types of solids. For example, conductivity and solubility can give great insight into the structure of a solid. For a substance to be soluble in water it must be charged or polar. (Remember the rule “like dissolves like.”) For a substance to be conductive, in any state, there must be charged particles in a mobile state so that they can complete a circuit. Model 3 – Solubility and Conductivity of Solids Substance Iron(II) sulfide Calcium bromide Sodium chloride Nitrogen molecular Water Carbon dioxide network covalent Diamond Silica Platinum metalic Brass Nickel ionic Chemical Formula Solubility in Water FeS CaBr2 NaCl N2 H 2O CO2 C SiO2 Pt Cu and Zn Ni Insoluble Very soluble Very soluble Slightly soluble N/A Slightly soluble Insoluble Insoluble Insoluble Insoluble Insoluble Conductive Conductive Conductive in as a Solid as a Liquid Aqueous Solution No No No No No No No No Yes Yes Yes Yes Yes Yes No Slightly No No No Yes Yes Yes N/A Yes Yes No N/A No N/A N/A N/A N/A N/A N/A = not applicable 12. Refer to Model 3. a. Which type(s) of solid is generally very soluble in water? ionic b. Which type(s) of solid is least soluble in water? network covalent and metallic 13. Refer to Model 3. a. Which type of solid is most conductive in the solid state? metallic b. Use the concepts you have learned about the type of solid in part a to explain why it is conductive in the solid state. electrons are loosely held 14. Explain why ionic substances would be conductive after they are melted, even though they are not conductive as solids. when melted the ions can freely move Extension Questions 15. The last column in Model 3 (Conductive in Aqueous Solutions) has several N/A entries. Give two reasons why conductivity data for those substances would not exist. 1) they dont dissolve in water 2) they are gases 16. Engineers use materials to perform different functions based on the properties of the materials. For centuries we have used metals for tools and more recently for electrical circuits. What properties of metallic solids make them well suited for this purpose? Metals are hard so they dont dissolve. Metals are also conductive because they have loosely held electrons