Metals and Metallurgy © 2009, Prentice-Hall, Inc. Sections 23.5-23.8 Metals and Metallurgy...

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Sections 23.5-23.8Metals and Metallurgy

Chemistry, The Central Science, 11th editionBrown & LeMay

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Physical Properties of Metals

• Metals– Conduct heat and

electricity.– Are malleable (can be

pressed or hammered into sheets).

– Are ductile (can be drawn into wire).

– Are packed so atoms can slip past each other.• So metals aren’t as brittle

as other solids.

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Electron-Sea Model

• Metals can be thought of as cations suspended in “sea” of valence electrons.

• Attractions hold electrons near cations, but not so tightly as to impede their flow.

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Electron-Sea Model

• This explains many of the properties of metals, like– Conductivity of heat

and electricity;– Deformation.

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Molecular Orbital Model• The electron-sea model does not explain

observed trends in melting point, boiling point, heat of fusion, etc.– The model suggests these properties should

increase with increasing number of valence electrons.

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Molecular Orbital Model

These trends can be explained by energy bands created by large number of molecular orbitals formed as metal atoms bond with each other.

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Molecular Orbital Model

• As with nonmetals, bond order apexes in center of row, then decreases.

• Thus, attractions (and melting point, etc.) apex in center of transition metals. (Group 6B)

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Alloys

• Alloys are mixtures of elements that have properties characteristic of metals.

• Many of the ordinary uses of metals involve alloys.

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Solution Alloys

• Components of alloys are dispersed uniformly—– In substitutional alloys,

solute particles take the place of solvent metal atoms.

– The particles in these alloys are quite close in size.

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Solution Alloys

• Components of alloys are dispersed uniformly.– In interstitial alloys, solute

particles find their way into the holes between solvent metal atoms.

– In this type of alloy the solute particles are smaller than the solvent particles.

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Intermetallic Compounds

• Intermetallic compounds are homogeneous alloys with definite properties and compositions.

• An example is Co5Sm,– which is used for

permanent magnets in headsets and speakers.

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Transition Metals

• Many important metals are included in this group.

• The transition metals are the elements in the d block of the periodic table.

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Physical Properties ofTransition Metals

• Some of their properties (such as ionization energy, atomic radius, etc.) are suggestive of isolated atoms.

• Others (such as density, melting point, etc.) suggest bulk solid metal.

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Atomic Radii

• Trends in atomic radii are similar across all three rows of transition metals.

• While Zeff increases across a row, so does the number of nonbonding electrons.– These repel each other

and increase the radius.

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Electron Configurations and Oxidation States

• Transition metals often have more than one common oxidation state.– Most have +2 state due

to loss of s electrons.– Oxidation numbers

greater than 2 are due to the loss of d electrons as well as s.

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Electron Configurations and Oxidation States

Many form compounds that have colors.

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Electron Configurations and Oxidation States

• Many have significant magnetic properties.– In diamagnetic elements, all

electron spins are paired.– Therefore, there is no net

magnetic moment.

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Electron Configurations and Oxidation States

• In paramagnetic atoms and ions, there are unpaired spins.

• The magnetic fields are randomly arranged, though, unless placed in an external magnetic field.

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Electron Configurations and Oxidation States

In ferromagnetic substances the orientations of magnetic fields from unpaired electrons are affected by spins from electrons around them.

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Electron Configurations and Oxidation States

When an external field is applied and then removed, the substance maintains the magnetic moment and becomes a permanent magnet.

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Chromium

• Chromium is oxidized by HCl or H2SO4 to form blue Cr2+ ion.

• Cr2+ is oxidized by O2 in air to form green Cr3+.

• Cr is also found in the +6 state as in CrO4

2− and the strong oxidizer Cr2O7

2−.

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Iron

• Iron exists in solution in +2 or +3 state.

• Elemental iron reacts with non-oxidizing acids to form Fe2+, which oxidizes in air to Fe3+.

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Iron

• Brown water running from a faucet is caused by insoluble Fe2O3.

• Fe3+ is soluble in acidic solution, but forms a hydrated oxide as a red-brown gel in basic solution.

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Copper

• In solution copper exists in the +1 or the +2 state.

• +1 salts are generally white and insoluble.

• +2 salts are commonly blue and water-soluble.