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An experiment designed to study the properties of elements in group 2a (alkaline earth elements) and group 7a (halogens) of the periodic table. The experiment involves observing and comparing the properties of the ions mg2+, ca2+, sr2+, ba2+, f-, cl-, br-, and i- through various tests. The goal is to identify an unknown ionic compound by determining the presence of its group 2a and group 7a ions.
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The periodic table arranges the elements in order of increasing atomic number into horizontal rows whose lengths are such that elements with similar properties recur periodically - that is, groups of similar elements fall into a single vertical column on the table. The elements in any vertical column of the periodic table are similar in their chemical properties, and are therefore considered to make up a chemical family. In this experiment, some of the properties of elements in two chemical families will be observed. These families are Group 2A, also known as the alkaline earth elements; and Group 7A, also known as the halogens. In each group, the four most important elements in the group will be studied. In Group 2A, these are magnesium (Mg), calcium (Ca), strontium (Sr), and barium (Ba). In Group 7A, they are fluorine (F), chlorine (Cl), bromine (Br), and iodine (I). These elements will be studied mostly in the form of ions, not as the neutral elements. All Group 2A elements react readily to lose two electrons and form ions with a +2 charge. All of the halogens readily gain one extra electron to form ions with a - 1 charge. In Part 1 of the experiment, some properties of the Group 2A cations Mg2+, Ca2+, Sr2+, and Ba2+^ will be observed and compared. In Part 2, some properties of the halide ions F, Cl-, Br-^ and I-^ will be studied. In part 3, an unknown ionic compound will be identified. The unknowns will be in the form of an aqueous solution and will contain a Group 2A cation and a Group 7A anion. In Parts 1 and 2, you will observe that the properties of the elements in a particular group of the periodic table are generally similar to each other but they are not identical to each other. The information that is obtained in parts 1 and 2 about the differences in properties of elements in each group will be used in Part 3 to determine which of these elements is present in the unknown. When the properties of elements in the same group of the periodic table are different from each other, it is usually found that the properties change in progression in the same order in which the elements are arranged on the periodic table. The following chart illustrates this for some properties of the halogens. The elements are listed on the chart in the same order in which they appear on the periodic table. Element Melting Boiling Density Ionization Point Point (as liquid) Energy F - 218 °C - 188 °C 1.11 g/mL 403 kcal/mol Cl - 101 °C - 34 °C 1.56 g/mL 302 kcal/mol Br - 7 °C + 59°C 3.12 g/mL 274 kcal/mol I +114 °C + 184 °C 4.93 g/mL 243 kcal/mol (as solid) Safety Precautions:
Waste Disposal: