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Experiment 17 - Periodic Properties of Elements: The Alkaline
Earth Elements and the Halogens
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:
• Wear your safety goggles.
• Silver nitrate (AgNO3) solutions will stain skin and clothes. If you suspect you may
have spilled AgNO3 on yourself, rinse it off immediately. The stains are dark brown
and they don’t show up right away. You’ll know the next day whether or not you
spilled AgNO3 on yourself.
