assignments --> Unit 3 part 4
Groups with metalloids
Characteristics of Group 17 of the periodic table.
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· Identify halogens.
· Describe physical and chemical properties of halogens.
· List some uses of halogens.
You’ve probably seen halogen lights like the ones pictured here. You may even have halogen lights in your home. If you do, you may have noticed that they get really hot and give off a lot of light for their size. A halogen light differs from a regular incandescent light bulb in having a small amount of halogen gas inside the bulb. The gas combines chemically with the metal in the filament, and this extends the life of the filament. It allows the lamp to get hotter and give off more light than a regular incandescent light without burning out quickly. What is halogen gas, and whichelementsare halogens? In this article, you’ll find out.
Meet the Halogens
Halogensare highly reactive nonmetallicelementsin group 17 of the periodic table. As you can see in the periodic table shown in theFigurebelow, the halogens include theelementsfluorine (F), chlorine (Cl), bromine (Br), iodine (I), and astatine (At). All of them are relatively common on Earth except for astatine. Astatine is radioactive and rapidly decays to other, more stable elements. As a result, it is one of the least common elements on Earth.
Q:Based on their position in the periodic table from theFigureabove, how many valenceelectronsdo you think halogens have?
A:The number of valenceelectronsstarts at one for elements in group 1. It then increases by one from left to right across each period (row) of the periodic table for groups 1–2 and 13–18. Therefore, halogens have seven valence electrons.
Chemical Properties of Halogens
The halogens are among the most reactive of all elements, although reactivity declines from the top to the bottom of the halogen group. Because all halogens have seven valenceelectrons, they are “eager” to gain one more electron. Doing so gives them a full outerenergy level, which is the most stable arrangement of electrons. Halogens often combine with alkalimetalsin group 1 of the periodic table. Alkali metals have just one valence electron, which they are equally “eager” to donate. Reactions involving halogens, especially halogens near the top of the group, may be explosive. You can see some examples in the video at the URL below. (Warning:Don’t try any of these reactions at home!)
Physical Properties of Halogens
The halogen group is quite diverse. It includes elements that occur in three differentstates of matterat roomtemperature. Fluorine and chlorine aregases, bromine is a liquid, and iodine and astatine aresolids. Halogens also varyincolor, as you can see in theFigurebelow. Fluorine and chlorine are green, bromine is red, and iodine and astatine are nearly black. Like other nonmetals, halogens cannot conduct electricity orheat. Compared with most other elements, halogens have relatively lowmeltingandboilingpoints. You can watch a lab demonstration of the melting and boiling points of halogens at this URL:http://www.youtube.com/watch?v=yP0U5rGWqdg.
Uses of Halogens
Most halogens have a variety of important uses. A few are described in theTablebelow.
Fluorine helps prevent tooth decay, so it is added to toothpaste as the compound sodium fluoride. You can learn how it protects teeth at this URL:http://www.animated-teeth.com/tooth_decay/t4_tooth_decay_fluoride.htm.
Chlorine is the active ingredient in household bleach. It removes stains from clothes. It can also be used to disinfect countertops and other surfaces.
Bromine is used to purifywaterin swimming pools and hot tubs. It reacts with bacteria and other germs and renders them harmless.
Iodine is added to alcohol and used as an antiseptic. It reacts with germs on cuts and wounds. Small amounts of iodine are also needed for good health. In the U.S., iodine is added to table salt to prevent iodine deficiencies. Does the salt you use contain iodine?
Q:Can you relate some of these uses of halogens to the properties of these elements?
A:The ability of halogens to kill germs and bleach clothes relates to their highly reactive nature.
· Halogens are highly reactive nonmetal elements in group 17 of the periodic table.
· Halogens includesolids,liquids, andgasesat roomtemperature, and they vary incolor.
· Halogens are among the most reactive of all elements. They have seven valence electrons, so they are very “eager” to gain one electron to have a full outerenergy level.
· Halogens have a variety of important uses, such as preventing tooth decay and killing germs.
TheTablebelowgives themeltingandboilingpoints of halogens. Create a graph with the data, and then describe in words the trends that you see in your graph.
1. What are halogens?
2. Why are halogens very reactive?
3. Describe the physical properties of halogens.
4. Why is chlorine added to swimming poolwater?
Characteristics of Groups 3 - 12 of the periodic table.
· Identify transitionmetals.
· List properties of transitionmetals.
· Describe thelanthanides and actinides.
What do all of the objects pictured above have in common? All of them are made completely or primarily of copper. Copper has an amazing variety of uses, including cooking pots, plumbing pipes, roofing tiles, jewelry,musical instruments, and electric wires. Copper is a good choice for these and many other objects because of its properties. It can be formed into wires and flat sheets, it’s a great conductor ofheatand electricity, it’s hard and strong, and it doesn’t corrode easily. In all these ways, copper is a typical transition metal.
What Are TransitionMetals?
Transition metalsare all theelementsin groups 3–12 of the periodic table. In the periodic table pictured inFigurebelow, they are theelementsshaded yellow, pink, and purple. The transition metals make up about 60 percent of all known elements. In addition to copper (Cu), well known examples of transition metals include iron (Fe), zinc (Zn), silver (Ag), and gold (Au) (Copper (Cu) is pictured in its various applications in the opening image). You can explore specific transition metals with the interactive periodic table at this URL:http://www.ptable.com/.
Q:Transition metals have been called the most typical of all metals. What do you think this means?
A:Unlike some other metals, transition metals have the properties that define the metals class. They are excellent conductors of electricity, for example, and they also have luster, malleability, and ductility. You can read more about these properties of transition metals below.
Properties of Transition Metals
Transition metals are superior conductors ofheatas well as electricity. They are malleable, which means they can be shaped into sheets, and ductile, which means they can be shaped into wires. They have highmeltingandboilingpoints, and all aresolidsat roomtemperature, except for mercury (Hg), which is a liquid. Transition metals are also high in density and very hard. Most of them are white or silvery incolor, and they are generally lustrous, or shiny. Thecompoundsthat transition metals form with otherelementsare often very colorful. You can see several examples in theFigurebelow.
Some properties of transition metals set them apart from other metals. Compared with the alkali metals in group 1 and the alkaline Earth metals in group 2, the transition metals are much less reactive. They don’t react quickly withwateror oxygen, which explains why they resistcorrosion.
Other properties of the transition metals are unique. They are the only elements that may useelectronsin the next to highest—as well as the highest—energy levelas valence electrons. Valence electrons are the electrons that form bonds with other elements incompoundsand that generally determine the properties of elements. Transition metals are unusual in having very similar properties even with different numbers of valence electrons. The transition metals also include the only elements that produce a magnetic field. Three of them have this property: iron (Fe), cobalt (Co), and nickel (Ni).
Q:How is the number of valenceelectronstypically related to the properties of elements?
A:The number of valenceelectronsusually determines how reactive elements are as well as the ways in which they react with other elements.
Those Elements Down Under
Transition metals include the elements that are most often placed below the periodic table (the pink- and purple-shaded elements in theFigureabove). Those that follow lanthanum (La) are called lanthanides. They are all relatively reactive for transition metals. Those that follow actinium (Ac) are called actinides. They are all radioactive. This means that they are unstable, so they decay into different, more stable elements. Many of the actinides do not occur in nature but are made inlaboratories.
· Transition metals are all the elements in groups 3–12 of the periodic table. More than half of all elements are transition metals.
· Transition metals are typical metals, with properties such as a superior ability to conduct electricity andheat. They also have the metallic properties of luster, malleability, and ductility. In addition, transition metals have highmeltingandboilingpoints and high density.
· Thelanthanides and actinidesare the transition metals that are usually placed below the main part of the periodic table. Lanthanides are relatively reactive for transition metals, and actinides are radioactive.
At the following URL, click on any two of the transition metals and read about their properties,atomic structure, discovery, and uses. Then write a paragraph comparing and contrasting the two elements.
1. What are transition metals?
2. Describe properties of transition metals.
3. How do transition metals differ from metals in groups 1 and 2? How are they different from all other elements?
4. Identify thelanthanides and actinides.
Groups with Metalloids
Characteristics of Groups 13 - 16 of the periodic table.
· Identifyelementsin groups 13–16 of the periodic table.
· List properties of a metalloid from each of these groups.
This image represents a famous ancient Egyptian named Tutankhamen. Do you see his heavy eyeliner? Most likely the eyeliner was made of a mineral containing antimony. This metalloid was commonly used for makeup by Egyptians between four and five thousand years ago. Today we know that antimony is toxic, although Tutankhamen probably didn’t know that. Antimony is found in group 15 of the periodic table. Group 15 is one of four groups of the periodic table that containmetalloids.
Groups 13–16 of the periodic table (orange in theFigurebelow) are the only groups that containelementsclassified asmetalloids. Unlike other groups of the periodic table, which contain elements in just one class, groups 13–16 contain elements in at least two different classes. In addition to metalloids, they also containmetals, nonmetals, or both. Groups 13–16 fall between the transition metals (in groups 3–12) and the nonmetals calledhalogens(in group 17).
Metalloidsare the smallest class ofelements, containing just six members: boron (B), silicon (Si), germanium (Ge), arsenic (As), antimony (Sb), and tellurium (Te). Metalloids have some properties ofmetals(elements that can conduct electricity) and some properties of nonmetals (elements that cannot conduct electricity). For example, most metalloids can conduct electricity, but not as well as metals. Metalloids also tend to be shiny like metals, but brittle like nonmetals. Chemically, metalloids may behave like metals or nonmetals, depending on their number of valenceelectrons. You can learn more about specific metalloids by clicking on the element symbols in the periodic table at this URL:http://www.chemicool.com/.
Q:Why does the chemical behavior of an element depend on its number of valenceelectrons?
A:Valenceelectronsare the electrons in an atom’s outerenergy levelthat may be involved inchemical reactionswith otheratoms.
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Group 13: Boron Group
Group 13 of the periodic table is also called the boron group because boron (B) is the first element at the top of the group (seeFigurebelow). Boron is also the only metalloid in this group. The other four elements in the group—aluminum (Al), gallium (Ga), indium (In), and thallium (Tl)—are allmetals. Group 13 elements have three valence electrons and are fairly reactive. All of them aresolidsat roomtemperature.