This photograph of the tungsten filament from a light bulb was taken with a scanning electron microscope. The filament is magnified more than 100 times. The diameter of the wire is about 15 µm, or 0.0015 cm.

The substance the researchers found was tungsten (W), a metal whose name means “heavy stone” in Swedish. Like most metals, tungsten is ductile. Tungsten has the highest melting point of any metal—3410°C. Tungsten has the lowest vapor pressure.

One challenge for researchers about 1900 was to find the best material for the filaments in light bulbs. The substance had to be ductile enough to be drawn into a narrow wire, could not melt at the temperatures produced when an electric current passes through a narrow wire, and had to have a low vapor pressure so that particles on the surface were not easily removed by sublimation.

Metallic Bonds Metal atoms achieve stable electron configurations by losing electrons. What happens if there are no nonmetal atoms available to accept the electrons? In a metal, valence electrons are free to move among the atoms. The metal atoms become cations surrounded by a pool of shared electrons. Notes

Metallic Bonds Notes metallic bond - attraction between a metal cation + the shared electrons that surround it. Although the electrons are moving among the atoms, the total number of electrons does not change. So, overall, the metal is neutral.

Metallic Bonds The more valence electrons an atom can contribute to the shared pool, the stronger the metallic bonds will be. The bonds in an alkali metal are relatively weak because alkali metals contribute only a single valence electron. Sodium is soft enough to cut with a knife and melts at 97.8°C. Transition metals, such as tungsten, have more valence electrons to contribute. Tungsten is a hard metal that melts at 3410°C.

Explaining Properties of Metals The mobility of electrons within metals affects the properties of metals. The ability to conduct an electric current and malleability are two important properties of metals. A metal has a built-in supply of charged particles that can flow. An electric current can be carried through a metal by the free flow of the shared electrons.

Metals are Malleable + + + + + + + + + Hammered into shape (bend). Ductile - drawn into wires. Electrons allow atoms to slide by. + + + + + + + + +

Explaining Properties of Metals In a metal, cations are surrounded by shared valence electrons. If a metal is struck, the ions move to new positions, but the ions are still surrounded by electrons. Metal changes shape but does not break. Hammer strikes metal.

How are the properties of alloys controlled? Scientists can design alloys with specific properties by varying the types and amounts of elements in an alloy. Notes Alloy mixture of two or more elements at least one of which is a metal have the characteristic properties of metals

Notes Alloy examples Bronze 1st important alloy contains only copper and tin Brass alloy of copper and zinc softer than bronze and is easier to shape shinier than bronze but is likely to weather more quickly

alloy of iron that contains small quantities of carbon Smart metal Steel alloy of iron that contains small quantities of carbon Smart metal Mixture of titanium & nickel

Alloys The properties of steel depend on which elements in addition to iron and carbon are used to make the steel and how much of those elements are included. Stainless steels contain more than 10 percent chromium by mass, but almost no carbon. Stainless steels are durable and do not rust. Stainless steels are more brittle than steels with more carbon.

Alloys The cables, towers, and deck of the Golden Gate Bridge contain steel. The steel in the cables needs to resist forces that pull on the cables. The steel towers needs to resist the compression forces caused by the weight they hold.

Alloys The surface of an object made from pure gold can easily be worn away by contact with other objects or dented because gold is a soft metal. When silver, copper, nickel, or zinc is mixed with gold, the gold is harder and more resistant to wear. These gold mixtures are alloys.

Alloys Bronze is hard and durable enough to be used for propellers on ships and for statues, such as these statues of horses. The French horn is made from brass, an alloy of copper and zinc.

Alloys Other Alloys The body of a plane is large and needs to be made from a lightweight material. Aluminum is lighter than most metals, but pure aluminum bends and dents too easily. Copper or manganese is added to aluminum to make a stronger material that is still lighter than steel. For some parts, even lighter materials are needed. Alloys of aluminum and magnesium are used for these parts.

What force holds the atoms of a metal together? Assessment Questions What force holds the atoms of a metal together? the attraction of a positively charged atom to a negatively charged atom the sharing of electrons between two atoms the gravitational force between dense metal atoms the attraction between metal cations and a pool of shared electrons

What force holds the atoms of a metal together? Assessment Questions What force holds the atoms of a metal together? the attraction of a positively charged atom to a negatively charged atom the sharing of electrons between two atoms the gravitational force between dense metal atoms the attraction between metal cations and a pool of shared electrons ANS: D

Why are solid metals good conductors of electric current? Assessment Questions Why are solid metals good conductors of electric current? Metals are good conductors because they can be drawn into wires. Metals are good conductors because they are solids at room temperature. The nuclei of metal atoms can move easily because they repel one another. Shared electrons are able to flow freely through the metal.

Why are solid metals good conductors of electric current? Assessment Questions Why are solid metals good conductors of electric current? Metals are good conductors because they can be drawn into wires. Metals are good conductors because they are solids at room temperature. The nuclei of metal atoms can move easily because they repel one another. Shared electrons are able to flow freely through the metal. ANS: D

Assessment Questions The properties of bronze depend on the ratio of iron, carbon, and small amounts of other elements in the alloy. True False

Assessment Questions The properties of bronze depend on the ratio of iron, carbon, and small amounts of other elements in the alloy. True False ANS: F, steel