Halogen Family (Group 17)

Halogens are highly reactive nonmetallic elements in Group 17 of the periodic table. As you can see in the periodic table shown in the picture below, the halogens include the elements fluorine (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.

image of the period table elements in group 17: halogens

The term "halogen" means "salt-former" because these elements will readily react with alkali metals and alkaline earth metals to form halide salts. The halogens all have seven valence or outer electrons. They are one electron short of having the full outer energy level, which makes them very reactive. The halogens are actually the most reactive nonmetals. Unlike metals, the reactivity declines from the top to the bottom of the halogen group making Fluorine the most reactive nonmetal.

The halogen group is quite diverse. It includes elements that occur in three different states of matter at room temperature. Fluorine and chlorine are gases, bromine is a liquid, and iodine and astatine are solids. Halogens also vary in color, as you can see in the picture below. Fluorine and chlorine are green, bromine is red, and iodine and astatine are nearly black. Like other nonmetals, halogens cannot conduct electricity or heat. Compared with most other elements, halogens have relatively low melting and boiling points.

image of chlorine, bromine, and iodine

Most halogens have a variety of important uses. Fluorine helps prevent tooth decay, so it is added to toothpaste as the compound sodium fluoride. 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 purify water in 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. The ability of halogens to kill germs and bleach clothes relates to their highly reactive nature.

To look at the Halogen Family and how they are used, please watch the video below:

Noble Gases (Group 18)

Noble gases: Helium, Ne, Ar, Kr, Xe

Noble gases are nonreactive, nonmetal elements in group 18 of the periodic table. As you can see in the picture below, noble gases include helium (He), neon (Ne), argon (Ar), krypton (Kr), xenon (Xe), and radon (Rn). All noble gases are colorless and odorless. They also have low boiling points, explaining why they are gases at room temperature. For an excellent overview of the noble gases, watch the video below.

image of the period table elements in the noble gas group

Noble gases are the least reactive of all known elements. That's because with eight valence electrons, their outer energy levels are full. The only exception is helium, which has just two electrons. But helium also has a full outer energy level, because its only energy level (energy level 1) can hold a maximum of two electrons. A full outer energy level is the most stable arrangement of electrons. As a result, noble gases cannot become more stable by reacting with other elements and gaining or losing valence electrons. Therefore, noble gases are rarely involved in chemical reactions and almost never form compounds with other elements.

Noble gases are used for balloons, light bulbs, and lighted signs. Although noble gases are chemically nonreactive, their electrons can be energized by sending an electric current through them. When this happens, the electrons jump to a higher energy level. When the electrons return to their original energy level, they give off energy as light. Different noble gases give off light of different colors. Neon gives off reddish-orange light, like the word "Open" in the sign below. Krypton gives off violet light and xenon gives off blue light.

Neon Sign image

So far in this lesson, we have learned a good deal about the Periodic Table. For a summary of the information found within this lesson, watch the videos below.

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