R40

Elements Handbook

Elements HandbookHandbook

Transition Metals

Before 1700Au

gold

Ag

silver

Cu

copper

Fe

iron

Hg

mercury

Zn

zinc

1700–1799Co

cobalt ~1735

Pt

platinum 1735

Ni

nickel 1751

Mn

manganese 1774

Mo

molybdenum 1778

W

tungsten 1783

Ti

titanium 1791

Y

yttrium 1794

Cr

chromium 1797

1800–1899V

vanadium 1801

Nb

niobium 1801

Ta

tantalum 1802

Pd

palladium 1803

Rh

rhodium 1803

Os

osmium 1803

Ir

iridum 1803

Cd

cadmium 1817

Zr

zirconium 1824

Ru

ruthenium 1844

Sc

scandium 1878

After 1900Lu

lutetium 1907

Hf

hafnium 1923

Re

rhenium 1925

Physical Properties

• Most transition metals are ductile, malleable, and good conductors of heat and electric current.

• For transition metals, density and melting point tend to increase across a series or increase to a peak in Group 6B and then decrease.

• Compounds of transition metals tend to have color.

Except for copper and gold, transition metals, including platinum, have a silvery luster.

Sources

• Transition metals come from mineral deposits in Earth’s crust. Minerals that are used for the commercial production of metals are called ores.

• For centuries, people have developed techniques for separating metals from ores. The ore is concentrated and the metal removed by reduction. Then the metal is refined and purified.

Gold exists as an element in nature. But its ore needs to be concentrated before the gold can be extracted and purified.

Density and Melting Points of Period 4 Transition Metals

3.0

9.0

0

6.0

Den

sit

y (

g/cm

3)

Sc

2.99

Cr

7.15

Mn Fe Co Ni Cu Zn

7.37.87

Ti

4.51

V

6.0

8.96

7.14

8.86 8.90

500

2000

1500

0

1000

Sc

1541

Cr

1907

Mn Fe Co Ni Cu Zn

1246

1538

Ti

1668

V

1910

1084

420

1495 1455

Tem

pera

ture

(�C

)

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Transition Metals R41

Atomic Properties

• Among the transition metals, as atomic number increases, there is an increase in the number of electrons in the second-to-highest occupied energy level.

• In periods 5 and 6, transition metals in the same group have identical or almost identical atomic radii. Consequently, these pairs of elements have very similar chemical properties. They tend to occur together in nature and are difficult to separate.

Chemical Properties

• There is great variation in reactivity among transition metals. Scandium and yttrium are similar to Group 1A and 2A metals. They are easily oxidized on exposure to air and react with water to release hydrogen. Platinum and gold are extremely unreactive and resist oxidation.

• In general, transition metals have multiple oxidation states. Compounds in which the elements are in their highest oxidation states are powerful oxidizing agents.

• Most transition metals form compounds with distinctive colors. The color of a transition metal compound or solution can indicate the oxidation state of the metal.

The oxidation number of vanadium is �5 in the yellow solution, �4 in the blue solution, �3 in the green solution, and �2 in the purple solution.

Trends in Atomic Size for Transition Metals

Increasing Atomic Number

120

130

140

150

160

170

180

190

Ato

mic

rad

ius (

pm

)

Sc

Y

Lu

Ti

HfZr

Cr

MoW

Tc

Fe

Ru

Os

Co Ni

PtAu

Ag

Zn

HgCd

V

TaNb

Mn

Rh

Re IrPd

Cu

Oxidation Numbers of Period 4 Transition Metals

�8

�6

�4

�2

0Sc Ti V Cr Mn Fe Co Ni Cu Zn

Ox

ida

tio

n N

um

be

rs

most common

VO43�

Cr2O72�

MnO4�

In these aqueous solutions, vanadium, chromium, and manganese are in their highest oxidation states.

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R42 Elements Handbook

Elements HandbookHandbook

Transition Metals

Catalytic Converters

In an internal combustion engine, some hydrocarbon molecules aren’t completely oxidized. They form carbon monoxide instead of carbon dioxide. Some hydrocarbon molecules even pass into the exhaust without reacting. At the high temperature and pressure inside an engine’s cylinders, some nitrogen from the air reacts with oxygen to produce irritating nitrogen oxides.

A catalytic converter keeps these pollutants from being released into the air. Inside the converter is a porous ceramic cylinder with a honeycomb structure. The ceramic absorbs particles of rhodium and platinum. The metals are catalysts for reac-tions that occur as exhaust gases pass through channels in the converter. Rhodium helps convert nitrogen oxides to nitrogen. Platinum helps convert hydrocarbons and carbon monoxide to carbon dioxide and water. ■

Cu Copper Alloys

Copper was one of the first metals to be widely used. It is found uncombined in nature or easily reduced from its ores. The Roman supply of copper came mainly from Cyprus and was known as aes Cyprium (metal of Cyprus). This name evolved to cyprium and then cuprium, which is why copper has the symbol Cu. Pure copper is valued both for its ability to conduct an electric current and its ability to resist corrosion.

Around 3500 BC, people began to add tin to copper to form bronze. This alloy is harder than pure copper and easier to melt for casting. Metalworkers could produce bronze with different properties by varying the amount of tin. Bronze used to make statues might contain as little as 10% tin by mass. Bronze used to make bells would contain 13–25% tin. Most copper coins are bronze with 4% tin and 1% zinc.

Brass is an alloy of copper and zinc. Brass is harder than pure copper and more malleable than bronze. Brass containing at least 65% copper can be worked when it is cold. Brass with 55–65% copper can be worked when it is hot. Before large amounts of gold and silver reached Europe in the 1500s, brass was the metal used for decorative items.

Copper that is exposed to oxygenand water forms a patina of basiccopper salts. This thin filmprotects the underlying metalfrom further oxidation. Thecomposition of the patina, itscolor, and the rate at which itforms vary with the climate. Therate is faster near the ocean. ■

When a bronze bell is struck, the clear, loud tone lasts for several seconds.

Ceramic withPt and Rh

Historically, brass was used to make high-quality scientific instruments. This microscope was made in 1765.

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Transition Metals R43

Fe Iron and Steel

Carbon is used to extract iron from its ores. At first, people used charcoal from burnt wood. In 1709, Abraham Darby invented a process that used coke instead of charcoal. Coke is almost pure carbon. It is produced when coal is heated and the impurities removed as gases. With coke, the production of iron became less expensive and more efficient.

Iron ore is reduced to metallic iron in a blast furnace. Ore, coke, and limestone are added at the top of the furnace. Molten iron and slag collect at the bottom. The “pig” iron produced contains 3–5% carbon and smaller amounts of other impurities, which make the iron brittle. Pig iron can’t be rolled or welded, but it can be cast. Cast iron is used to make stoves and engine blocks for cars.

Most pig iron is used to make steel. The methods for making steel differ, but they all lower the carbon content to less than 2% and remove other impurities. About 90% of the steel produced is carbon steel, which contains no other metals. Mild steel, which is malleable and ductile, contains less than 0.2% carbon. Medium steel (0.2% to 0.6% carbon) is used for structural components, such as beams and girders. Because high-carbon steel (0.8% to 1.5% carbon) is harder than other carbon steels, it is used to make items such as drill bits and knives.

Transition metals are used to produce alloy steels with a specific set of properties. The most common stainless steel contains about 18% chromium and 8% nickel. ■

Iron ore typically contains Fe2O3, and SiO2. When heated, limestone produces CaO, which reacts with SiO2 to form slag. Slag is used to manufacture Portland cement.

In 1779, Abraham Darby III built the world’s first cast-iron bridge across the River Severn in England. The bridge is still used by pedestrians.

Insulation

Oxygen-rich air

Molten iron

Slag

Exhaust gases(CO, CO2, N2)

Iron ore, coke,limestone

200�C

800�C

1300�C

1900�C

Blast Furnace

Did You Know...Did You Know...??Swords made with Damascus steel were highly valued. The source of this quality was the 0.02% vanadium in the iron ore that the steel makers used. When they began to use a different source of iron ore, the quality of their steel declined.

Transition Metals R43

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Elements Handbook

Elements HandbookHandbook

Transition Metals

Phytoremediation

Phytoremediation uses plants such as sunflowers, Indian mustard, and dandelions to remove pollutants from contaminated soil and water. The contaminants include organic solvents, pesticides, and toxic metals such as cadmium and chromium.

Plants have a natural ability to absorb nutrients through their roots. Often a plant does not distinguish a toxic metal such as cadmium from a nutrient such as zinc because these metals have similar chemical properties. So cadmium is absorbed and transported to the leaves and stems, where it accumulates.The plants are composted or burned after harvesting.The metal residues are buried in an approved landfill or recovered through smelting.

■

Fe Ni Co

Permanent Magnets

Refrigerator magnets contain a barium ferrite, BaO

•

6Fe

2

O

3

, or strontium ferrite, SrO

•

6Fe

2

O

3

, powder, which is embedded in plastic or rubber. Horseshoe magnets usually contain an alloy of aluminum, nickel, and cobalt.

Iron, nickel, and cobalt are strongly attracted to magnetic fields. When these metals are exposed to a magnetic field, their cations line up in an orderly arrangement. When the field is removed, the ions remain lined up, and the material can act as a magnet. This type of magnetism is called ferromagnetism.

A magnet retains its strength unless it is heated past a point called the Curie temperature. For iron, this temperature is 1043 K. For cobalt, it is 1388 K. For nickel, it is 627 K.

Magnets made from a neodymium, boron, and iron alloy are very powerful. If they are allowed to fly together, they will shatter. They are used to check for counterfeit bills because they can detect tiny magnetic particles placed in the ink of genuine bills.

■

The wrench is strongly attracted to the tiny neodymium-iron-boron cube.

Au

Gold

Gold occurs chiefly as small flecks of free metal in veins of quartz. About 5 g of gold is produced from a metric ton (10

6

g) of gold-bearing rock.

Gold can be pounded into sheets so thin that they will transmit light. These sheets, called gold leaf, are used for lettering and decoration in general. Gold is used on the outside surfaces of satellites because it resists corrosion. Its high electrical and thermal conductivity make gold a good choice to plate contacts in microcircuits.

Pure gold is alloyed to make it harder and more durable. Gold alloys are safe to use as fillings for teeth because gold is highly unreactive.

Units called karats (k) are used to describe the purity of gold. Pure gold is 24k or 100% gold. Gold in coins is usually 22k or 92% gold. Gold in rings is often 14k (58%).

■

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R45

Micronutrients

Trace amounts of some transition metals are essential for human health.

Iron is found mainly in hemoglobin and myoglobin. Hemoglobin is the protein that transports oxygen in blood. Myoglobin is the protein that stores oxygen in muscle tissue. Vitamin C helps the absorption of iron by promoting the reduction of Fe3� ions to Fe2�ions.

Zinc is a cofactor in many enzymes. It helps protect the immune system. Hormones that control growth and reproduction do not function properly without zinc. A lack of zinc impairs the sense of taste and reduces the appetite.

Copper is a component of enzymes that control the synthesis of melanin, hemoglobin, and phospho-lipids in the sheath that protects nerves.

Molybdenum affects the absorption of copper. It is also needed for the oxidation of lipids and the metabolism of sulfur and nitrogen.

Chromium assists in the metabolism of glucose and may help to control adult-onset diabetes. A lack of chromium may affect growth.

Manganese is required for the proper function of the nervous system and the thyroid gland. It is needed for glucose metabolism. It helps maintain healthy bones and cartilage.

Cobalt is a component of vitamin B12, which is required for the synthesis of red blood cells. ■

Ti Suncreens

You need some exposure to sunlight so your skin cells can make vitamin D, which is needed for healthy bones and teeth. Yet the UV radiation in sunlight can damage skin cells and even lead to skin cancer. The best way to protect your skin is to limit your time in the sun. The next best way is to use a sunscreen.

All the active ingredients in sunscreens protect against UVB light (280–320 nm), which is the primary cause of sunburn. Some protect against UVA light (320–400 nm), which penetrates deeper and causes long-term damage. A sun protective factor rating (SPF) measures only how effective a sunscreen is against UVB, not UVA.

Titanium dioxide, TiO2, can reflect and scatter UV light. This stable and nonirritating oxide has one drawback. It looks like white paint on the skin. One manufacturer has addressed this problem by decreasing the size of the TiO2 particles to a diameter of about 21 nm. At this size, TiO2 appears transparent because its particles are smaller than wavelengths of visible light and light isn’t reflected by the particles. ■

Transition Metal Micronutrients

*Recommended Dietary Allowance or Adequate Intake

Element RDA or AI* Dietary Sources

Iron 10 mg RDA (M)20 mg RDA (F)

liver, green vegetables, egg yolk, fish, whole wheat, nuts, oatmeal, molasses, and beans

Zinc 11 mg RDA (M)8 mg RDA (F)

liver, eggs, meat, milk, whole grains, and shellfish

Copper 900 µg RDA beans, peas, and shellfish

Molybdenum 45 µg RDA beans, peas, and whole grains

Chromium 35 µg AI (M)25 µg AI (F)

meat and whole grains

Manganese 2.3 mg AI (M)1.8 mg AI (F)

nuts, whole grains, dried fruits, and green leafy vegetables

Did You Know...Did You Know...??An octopus has blood that is blue, not red, because the compound that trans-ports oxygen in an octopus contains copper, not iron. Snails, oysters, and spiders are also bluebloods.

Transition Metals R45

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