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Metalsand
Metallurgy
© 2009, Prentice-Hall, Inc.
Sections 23.5-23.8Metals and Metallurgy
Chemistry, The Central Science, 11th editionBrown & LeMay
Metalsand
Metallurgy
© 2009, Prentice-Hall, Inc.
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.
Metalsand
Metallurgy
© 2009, Prentice-Hall, Inc.
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.
Metalsand
Metallurgy
© 2009, Prentice-Hall, Inc.
Electron-Sea Model
• This explains many of the properties of metals, like– Conductivity of heat
and electricity;– Deformation.
Metalsand
Metallurgy
© 2009, Prentice-Hall, Inc.
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.
Metalsand
Metallurgy
© 2009, Prentice-Hall, Inc.
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.
Metalsand
Metallurgy
© 2009, Prentice-Hall, Inc.
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)
Metalsand
Metallurgy
© 2009, Prentice-Hall, Inc.
Alloys
• Alloys are mixtures of elements that have properties characteristic of metals.
• Many of the ordinary uses of metals involve alloys.
Metalsand
Metallurgy
© 2009, Prentice-Hall, Inc.
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.
Metalsand
Metallurgy
© 2009, Prentice-Hall, Inc.
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.
Metalsand
Metallurgy
© 2009, Prentice-Hall, Inc.
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.
Metalsand
Metallurgy
© 2009, Prentice-Hall, Inc.
Transition Metals
• Many important metals are included in this group.
• The transition metals are the elements in the d block of the periodic table.
Metalsand
Metallurgy
© 2009, Prentice-Hall, Inc.
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.
Metalsand
Metallurgy
© 2009, Prentice-Hall, Inc.
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.
Metalsand
Metallurgy
© 2009, Prentice-Hall, Inc.
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.
Metalsand
Metallurgy
© 2009, Prentice-Hall, Inc.
Electron Configurations and Oxidation States
Many form compounds that have colors.
Metalsand
Metallurgy
© 2009, Prentice-Hall, Inc.
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.
Metalsand
Metallurgy
© 2009, Prentice-Hall, Inc.
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.
Metalsand
Metallurgy
© 2009, Prentice-Hall, Inc.
Electron Configurations and Oxidation States
In ferromagnetic substances the orientations of magnetic fields from unpaired electrons are affected by spins from electrons around them.
Metalsand
Metallurgy
© 2009, Prentice-Hall, Inc.
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.
Metalsand
Metallurgy
© 2009, Prentice-Hall, Inc.
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−.
Metalsand
Metallurgy
© 2009, Prentice-Hall, Inc.
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+.
Metalsand
Metallurgy
© 2009, Prentice-Hall, Inc.
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.
Metalsand
Metallurgy
© 2009, Prentice-Hall, Inc.
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.