Virtual lab determining bond types answers

Name Class Date Copyright © Houghton Mifflin Harcourt Publishing Company Virtual Lab Determining Bond Types When working with this Lab Report file, remember to save often. PROBLEM Chemical bonds are not really directly observable. But just as the properties of elements allow you to place them into groups such as metals and nonmetals, the properties of substances made of atoms bonded together suggest that the types of bonds can be clustered into several different groups. In this virtual lab simulation, you are challenged to discover which properties of materials are found with which bond types, in order to identify some unknowns. Background Despite being portrayed in some models as “sticks” between atoms, chemical bonds are not quite so simple. For a pair of atoms at certain distances, pushing them closer together requires a lot of energy, but pulling them apart also requires a lot of energy. As a consequence, the pair of atoms tends to remain at that comfortable distance. The theory of chemical bonding was developed as an explanation for these observations. The energy differences are greatest for bonds between metal and nonmetal atoms. These bonds are described as being ionic. Ionic bonds are treated in chemical bonding theory as if the metal atom had become positively charged by releasing an electron and the nonmetal atom had become negatively charged by absorbing one. This theory explains a number of properties of substances containing these types of bonds. The solid form of these substances has a regularly shaped crystal form, is very hard, and does not conduct electricity, as if the ions were trapped in a network of strong bonds. The particles often break apart in water and can conduct electricity when they are dissolved in water. The bonds are hard to break, but if you do manage to break them, either by dissolving in water or by melting the substance at high temperatures, the substance will conduct electricity, even though the solid crystal does not. Another type of bond, a covalent bond, occurs mostly between nonmetal atoms. The energy differences for these bonds are typically not quite as great as for ionic bonds. In theory, covalent bonds are treated as if the atoms were sharing a pair of electrons without either atom becoming a charged ion. As was the case with ionic bonds, the theory of the covalent bond explains many of the properties of these substances. They are not as hard, as if the groups of atoms were not all held together in a network, and they’re easier to melt. Usually these substances do not conduct electricity, whether they are solid, liquid or dissolved in water, or gas. The last type of bonding, metallic bonding, is found whenever different metal atoms are bonded to each other. According to bonding theory, a metallic bond consists of atoms held together by a shared attraction for electrons. Unlike in covalent bonding, all of the metal atoms are assumed to share all of the electrons equally, and the electrons are thus free to move around. Because the electrons are free to move around, metals conduct electricity well, whether in solid or liquid form. In addition, metals tend to be bendable and melt at lower temperatures than ionic compounds do, because the atoms are not held so tightly together. PLANNING Goal Infer the types of bonds contained in a substance based on observations of its properties, as compared to properties typical for substances containing covalent, ionic, and metallic bonds. Objectives Test some properties of different substances to infer which bond types they contain. Relate the observable properties of the substance to the characteristics of different bond types. Infer the types of bonds a substance contains. Materials This virtual lab requires: • A computer capable of running the simulation • A sound card with speakers to play the audio • An Internet browser with Adobe Flash Player 10 or above installed Electrical Safety Exercise caution when working with electrical equipment such as computers. Do not use electrical equipment with frayed or twisted wires. The area under and around electrical equipment should be dry; cords should not lie in puddles of spilled liquid. Reality Check The processes for several of these tests have been simplified for the purposes of this lab. An advantage of the virtual lab is that you can test the conductivity of molten substances at temperatures that cannot be achieved in most school laboratories. Another advantage is that the tests can be redone over and over with the same sample. In an actual lab, recovering the sample may not be so simple. Your Plan 1. Adjust or replace the following sample procedure to suit your plan for performing the virtual lab. Be sure to provide more detail about what order you will use in testing the substances and their properties. Also indicate what observations you will need to make for each property.