6.4 the structure of metals this photograph of the tungsten filament from a light bulb was taken...

6.4 The Structure of Metals

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.


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.

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

Notes


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.

Metallic Bonds


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.

Explaining Properties of Metals


Metals are Malleable• Hammered into shape (bend).

• Ductile - drawn into wires.

• Electrons allow atoms to slide by.

+ + + ++ + + +

+ + + +


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.

Explaining Properties of Metals

Hammer strikes metal. Metal changes shape but does not break.


How are the properties of alloys controlled?

Alloys

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


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

Notes


• Steel– alloy of iron that contains small quantities of carbon

• Smart metal– Mixture of titanium & nickel


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.

Alloys


Assessment Questions

1. What force holds the atoms of a metal together? a. the attraction of a positively charged atom to a

negatively charged atom

b. the sharing of electrons between two atoms

c. the gravitational force between dense metal atoms

d. the attraction between metal cations and a pool of shared electrons



1. What force holds the atoms of a metal together? a. the attraction of a positively charged atom to a

negatively charged atom

b. the sharing of electrons between two atoms

c. the gravitational force between dense metal atoms

d. the attraction between metal cations and a pool of shared electrons

ANS: D



2. Why are solid metals good conductors of electric current?a. Metals are good conductors because they can be drawn

into wires.b. Metals are good conductors because they are solids at

room temperature.c. The nuclei of metal atoms can move easily because

they repel one another.d. Shared electrons are able to flow freely through the

metal.



2. Why are solid metals good conductors of electric current?a. Metals are good conductors because they can be drawn

into wires.b. Metals are good conductors because they are solids at

room temperature.c. The nuclei of metal atoms can move easily because

they repel one another.d. Shared electrons are able to flow freely through the

metal.

ANS: D



1. The properties of bronze depend on the ratio of iron, carbon, and small amounts of other elements in the alloy.

TrueFalse



1. The properties of bronze depend on the ratio of iron, carbon, and small amounts of other elements in the alloy.

TrueFalse

ANS: F, steel

6.4 the structure of metals this photograph of the tungsten filament from a light bulb was taken...

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