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Hydrogen:
Alone in the upper left corner of the periodic table is hydrogen –
the element with the simplest and smallest atoms. Each hydrogen atom has
one proton and one electron. Some hydrogen atoms also have neutrons. Because
the chemical properties of hydrogen are greatly different than those of
the other elements, it really cannot be grouped into a family. Although
hydrogen makes up more than 90 percent of the atoms in the universe, it
makes up only 1 percent of the mass of Earth’s crust, oceans and
atmosphere. Hydrogen is rarely found on Earth as a pure element. Most
hydrogen is combined with oxygen in water (H20).
Carbon:
Carbon is the only nonmetal in Group 14. Each element in this group has
atoms that can gain, lose, or share four electrons when reacting with
other elements. Compounds made of molecules containing long chains of
carbon atoms are found in all living things.
Nitrogen
Family: Group 15, the nitrogen family, contains only two nonmetals:
nitrogen and phosphorus. These nonmetals usually gain or share three electrons
when reacting with other elements. The atmosphere is almost 80 percent
nitrogen gas (N2). It does not readily react with
other elements, but phosphorus does.
Oxygen
Family: Group 16, the oxygen family, contains three nonmetals:
oxygen, sulfer, and selenium. These elements usually gain or share two
electrons when reacting with other elements. Oxygen is highly reactive
and can combine with almost any other element. It is also the most abundant
element in Earth's crust and the second-most abundant element in the atmosphere.
The
Halogen Family: The elements in Group 17 are commonly known as
halogens, from Greek words meaning “forming salts.” Halogens
are very reactive nonmetals that, when in their uncombined form, are dangerous
to human. Even though they are dangerous, many of the compounds that halogens
form are useful. They easily form compounds called salts with many metals.
Because they are so reactive, halogens are often used to kill harmful
microorganisms. For example, the halogen chlorine is used to clean drinking
water and to prevent the growth of algae in swimming pools.
The
Noble Gases: Group 18 elements are called the noble, or inert,
gases because they almost never react with other elements. Because they
are so un-reactive, the noble gases were not discovered until the late
1800s. All the noble gases exist in Earth’s atmosphere, but only
in small amounts. For example, argon gas makes up about one percent of
the atmosphere. Colorful lights are made by passing an electric current
through tubes filled with neon, krypton, xenon, or argon gas. |
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