Chemistry - A Molecular Science

The chemical properties of an elemen

t can be determined from its group:

Hydrogen

is unique as shown by its position in the periodic table in Figure 1.8. It normally forms a +1 ion, which would put it into Group 1A, where it is placed in the periodic table on the back cover. However, it is a nonmetal and can also form compounds in which it is a -1 ion, which is more

consistent with the Group 7A elements.

Group 1A

elements are known as the

alkali metals

. All members of this family are very

reactive, readily losing one electron to form +1 ions.

Group 2A

elements are known as the

alkaline earth metals

. They are also very reactive

but not as reactive as the 1A’s. They occur as +2 ions in their compounds.

Groups 1B - 8B

elements are the

transition metals

. Most form a +2 ion, but +1 and +3 ions are

also found. Unlike the 1A and 2A metals, many transition metals can form more than one type of ion, such as Fe

2+ and Fe

3+.

Group 3A

elements are metals, except for boron, which is a metalloid. They typically form +3 ions. Thallium (Tl) forms both +3 and +1 ions.

Group 4A

elements demonstrate that metallic character also increases in going down a group. Carbon is a nonmetal and does not typically form ions. Silicon and germanium are metalloids, but tin and lead are metals that form +2 ions.

Group 5A

elements also progress from nonmetallic at

the top to metallic at the bottom.

Nitrogen and phosphorus are nonmetals,

which can form -3 ions. Arsenic,

antimony, and bismuth increase in their tendency to form +3 ions.

Group 6A

elements display only gradual changes in their chemistry, except for the chemistry of oxygen, which differs subst

antially from the other members. Oxygen,

sulfur, and selenium are nonmetals; tellurium is a metalloid, and polonium is a radioactive

metal

.^

Group 7A

elements are known as the

halogens

. They are very reactive, readily forming -1

ions. In fact, they are found in nature only in compounds such as NaCl and MgF

.^2

Group 8A

elements are known as the

noble gases

because they show little tendency to

react with other substances. There are

no known compounds of helium, neon or

argon and only a very few of krypton and xenon. Radon is radioactive.

Chapter 1 The Early Experiments

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