Figure 11 The halogens are a group of elements that are important to us in a variety of ways. Chlorine is added to drinking water to kill bacteria.
Iodine is needed by many systems in your body.
Group 18 The Noble Gases
K CHAPTER 4 Periodic Table
(t)Don Farrall/PhotoDisc, (b)Matt Meadows
Fluorine 9 F
Group 17 The Halogen Group
Chlorine 17 Cl
Bromine 35 Br
Iodine 53 I
Astatine 85 At
Group 17—The Halogen Group All the elements in Group 17 are nonmetals except for astatine, which is a radioac- tive metalloid. These elements are called halogens, which means “salt-former.” Table salt, sodium chloride, is a substance made from sodium and chlorine. All of the halogens form similar salts with sodium and with the other alkali metals.
The halogen fluorine is the most reactive of the halogens in combining with other elements. Chlorine is less reactive than fluo-
Helium 2 He
Neon 10 Ne
Argon 18 Ar
Krypton 36 Kr
Xenon 54 Xe
Radon 86 Rn
rine, and bromine is less reactive than chlorine. Iodine is the least reactive of the four nonmetals. Figure 11 shows some uses of halogens.
What do halogens form with the alkali metals?
Group 18—The Noble Gases The Group 18 elements are called the noble gases. This is because they rarely combine with other elements and are found only as uncombined elements in nature. Their reactivity is very low.
Helium is less dense than air, so it’s great for all kinds of balloons, from party balloons to blimps that carry television cameras high above sporting events. Helium balloons, such as the one in Figure 12, lift instruments into the upper atmosphere to measure atmospheric conditions. Even though hydrogen is lighter than helium, helium is preferred for these pur- poses because helium will not burn.