Scientist:
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UNIT 1:
ATOMS AND ELEMENTS
#7
Reading: Groups of the Periodic Table
Alkali Metals (Group 1A)
The Alkali metals, found in group 1A of the periodic
table are extremely reactive metals. The word
“alkali” or “alkaline” refers the chemical property
of these elements to react with other elements to
form a special kind of chemical compound called a base (we will learn about these later…
but you may have heard of acids and bases, or perhaps alkaline batteries). Because the
Alkali Metals are so chemically reactive, these elements do not exist in nature in their pure
form. Pure samples of these elements must be produced through chemical reactions. As
with all metals, the alkali metals are malleable, ductile, and are good conductors of heat and
electricity. The Alkali Metals are softer than most other metals, and can easily be cut with a
butter knife. They have low densities and will float on water. Cesium and francium are the
most reactive elements in this group. Alkali metals can explode if they are exposed to
water. They also react to the oxygen in the air, forming a gray oxide layer on the metal’s
surface.
Alkaline Earth Metals (Group 2A)
The Alkaline Earth Metals are metallic elements found in
the second group of the periodic table. They are shiny, and
have a silvery-white appearance. The Alkaline Earth Metals
are also very reactive, but slightly less so than the Alkali Metals mentioned above. Because
of their reactivity, the Alkaline Earth Metals are not found in nature in their pure elemental
form… they are always bonded to other elements in various rocks and minerals. For
example, calcium is the fifth most abundant element in the earth’s crust, but is only found
in minerals such as chalk, limestone, and gypsum.
Transition Metals (“B” Groups)
The 38 elements in the “B Groups” of the periodic
table are called "Transition Metals". As with all
metals, the transition elements are both ductile
and malleable, and conduct electricity and heat. While the Alkali Metals (1A) and Alkaline
Earth Metals (2A) both demonstrate predictable patterns in their chemical behavior based
on their group, the Transition Metals tend to be more complex and a little more
unpredictable. They also tend to be much more stable than their counterparts in Groups
1A and 2A, and pure samples of many transition metals exist in
nature. Familiar metals such as iron, nickel, chromium, and titanium
are known for their strength, shine, and stability. The precious
metals in Group 11 (1B) include copper, silver, and gold, used for
jewelry and for making coins. In addition, three Transition Metals - iron, cobalt, and nickel
- are the only elements known to produce a magnetic field.
Halogens (Group 7A)
The halogens are five non-metallic elements
found in Group 7A of the periodic table. The
term "halogen" means "salt-former" and
compounds containing halogens are called
"salts". Table salt (NaCl) is just one example of a chemical “salt” but many other chemical
compounds are called salts as well, such as magnesium bromide (MgBr2), aluminum
fluoride (AlF3), and potassium chloride (KCl). The halogens represent all three states of
matter at room temperature: fluorine and chlorine are both gases, bromine is a liquid, and
iodine is a solid. The halogens are extremely reactive; they are the most reactive
nonmetals. Fluorine, at the top of the group is particularly ferocious and is often
considered the most reactive element on the Periodic Table. A balloon filled with fluorine
gas is so volatile it can be ignited with the flash of a camera and hydrofluoric acid
(containing fluorine) is exceptionally dangerous.
The halogens are arguably the most important group on the Periodic Table when
discussing manufacturing and industry. Fluorine is used to help break chemical
compounds down and to isolate elements. Chlorine is used as a bleaching agent to make
materials such as paper turn white. Various chemical compounds containing chlorine are
used to kill bacteria and microorganisms in drinking water
and also as a powerful insecticide in the agricultural
industry. A halogen light bulb contains small amounts of
iodine or bromine, which allows the light bulb to operate at
higher temperatures than a standard light bulb.
Noble Gases (Group 8A)
As the name suggests, all of the elements in
Group 8A are gases. In addition, the Noble Gases
are the most stable – that is, nonreactive elements on the Periodic Table. The noble gases
are almost never involved in chemical reactions.
Another word for nonreactive is “inert.” Because the Noble Gases are invisible and do not
react, it took a long time to discover them. Helium, now used in party balloons, was
discovered in 1895… over 100 years after the more reactive gases oxygen, chlorine, and
nitrogen were discovered in the 1770s.
Passing an electric current through neon will bring out its familiar
glow. The other Noble Gases, deliver similar results as well.
Check for Understanding
1) The most reactive metals on the Periodic Table are in which group? ___________________
2) What about nonmetals? Which is the most reactive nonmetal group?________________
3) Where are the most stable elements on the Periodic Table? _____________________________
4) Can we find pure sodium metal in nature? Why or why not? __________________________
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5) Can we find pure argon in nature? Why or why not? ___________________________________
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6) What is the most reactive nonmetal?
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7) What is the most reactive metal?
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