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MetalsMetals
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Properties of Metals Luster
Malleability
Ductility
High thermal and
electrical conductivity
Hardness
These properties are the
result of non directional
covalent bonding found
in metallic crystals 2
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Packing in MetalsPacking in Metals
Model:Model: Packing uniform, hard spheres to best usePacking uniform, hard spheres to best useavailable space. This is calledavailable space. This is called closest packingclosest packing. Each. Eachatom has 12 nearest neighbors.atom has 12 nearest neighbors.
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Metal atoms slide or roll past one another
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Closest PackingClosest Packing
HolesHoles
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Gold atom packing
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Metal atoms arrange themselves
so that they are as close together
as possible (lowest possible PE),
while minimizing the repulsionbetween their nuclei
Each metal has a characteristic, lowest energy
arrangement of atoms which is called its
crystal structure
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Electron Sea Model
Metal atoms become cations
All valence electrons are delocalized andpooled together
A network of positive ions is immersed in a
mobile sea of electrons
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Mobile e- flowthroughout metal
crystal, enabling
metallic properties
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Band Model
Electrons travel within molecular orbitalsformed by the valence orbitals of the metallicatoms
When many metal atoms interact, the largenumber of resulting molecular orbitals becomemore closely spaced and finally form a virtualcontinuum of levels, called bands
Molecular orbitals occupied by conducting
electrons are called conduction bands
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orma on o an energy an n ummetal
As more and more Li atoms are added to the growing molecule, Li2, Li3, . . . ,
additional energy levels are added and the spacing between levels becomes
increasingly smaller. In an entire crystal ofNatoms, the energy levels merge
into a band ofNclosely spaced levels 11
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In band theory of conductivity, delocalized electrons move
freely through bands formed by overlapping molecular orbitals.
Mg 1s22s22p63s2 or [Ne]3s2
e-
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Energy Gaps Between Valence and Conduction Bands in
Metals, Semiconductors and Insulators
e-
e-
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Metals are malleable and ductile
Malleability: ability to pound a piece of metal into a thin sheet.
Ductility: ability to draw a piece of metal into a thin wire.
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When a piece of metal is hammered or
stretched, the atoms slide or roll past one
another. The metal atoms rearrangethemselves within the electron sea to
assume the new shape without breaking
their metallic bonds.
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Metals are good conductors of electricity
When an electric current (a stream ofe-) is
passed through a metal, the e- are free to move
from metal ion to metal ion.
The more freely they move through the metal,
the better conductor it is. Ag is the best conductor
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Metals are good conductors of heat
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Metals have luster
When light hits a metal
surface, the free valence e-on the surface absorb andthen re-emit the lightenergy,
which makes the
surface of the metal
appear shiny 17
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Hardness and Melting Points
The hardness and melting point of a metal depend to a
large extent on how many valence electrons the metal hasto participate in metallic bonding.
The greater the number of valence electrons, the more
firmly the metal ions are held in place.
Moving left to right across a period, the hardness andmelting points of metals generally increases as the
number of valence electrons available for metallic bonding
increases.
Alkali metals (Li, Na, K) have only one valence electron sothey are very soft metals with low melting points. Alkaline
Earth (Mg, Ca, Sr) have two valence electrons, so they are
harder than the Alkali metals and have higher melting
points. 18
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Density The density of metals depends on the average
atomic mass of the atoms, and also on how the
metal ions are packed together to form its crystal
structure.
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osmium, Os, 22.61 g/cm3
iridium, Ir, 22.56 g/cm3
platinum, Pt, 21.4 g/cm3
rhenium, Re, 21.0 g/cm3
neptunium, Np, 20.4 g/cm3
plutonium, Pu, 19.8 g/cm3
gold, Au, 19.3 g/cm3
tungsten, W, 19.3 g/cm3
mercury, Hg, 13.53 g/cm3
lead, Pb, 11.4 g/cm3
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Why is mercury a liquidWhy is mercury a liquid
at STP?at STP?
Mercury hangs on to its valence 6s
electrons very tightly.
Mercury-mercury bonding is very
weak because its valence
electrons are not shared readily.
http://antoine.frostburg.edu/chem/senese/101/periodic/faq/why-is-mercury-
liquid.shtml
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Floating Billiard Ball?!Floating Billiard Ball?!
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Li id Mi th M ?Li id Mi th M ?
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Liquid Mirrors on the Moon?Liquid Mirrors on the Moon?
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3.7-m diameter liquid mirror at Laval University. The liquid is mercury.
There are no detectable mercury vapors in the air because a thin transparent
layer of oxide covers the surface.
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A mineralis a naturally occurring substance with a range of
chemical compositions.
An ore is a mineral deposit concentrated enough to allow
economical recovery of a desired metal.
Metallurgyis the science and technology of separating metals
from their ores and of compounding alloys.
An alloyis a solid solution either of two or more metals, or of a
metal or metals with one or more nonmetals.
Recovery of a metal from its ore:
1. Preparation of the ore
2. Production of the metal
3. Purification of the metal
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Mn nodules on the ocean floor
All i t
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Alloys: mixturesof metals that
give uniqueproperties
Alloys are solutions!
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Usually much harder and
stronger than pure metals
because:
1. additional valence electronsincreases the strength of the
metallic bonding
2. Smaller atoms will interfere
with how easily the metal atoms
can slide past one another
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Metal Alloy TypesMetal Alloy Types
Substitutional Alloy::
some metal atomsreplaced by others
of similar size.
brass = Cu/Zn
Interstitial Alloy:
Interstices (holes) in
closest packed metalstructure are occupied by
small atoms.
steel = iron + carbon
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Examples of Alloy Composition
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Coins are alloys too
Copper is used in all U.S. coins.
By 1982, the price of copper rose to where it was costingthe U.S. Treasury Department more than 1 cent to make a
penny.
Since then, to conserve copper and reduce costs, the
penny has been made of 97.5% zinc and 2.5% copper,
with the zinc core sandwiched between two thin layers of
copper.
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$10,000 penny?!
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Where did all the old quarters go?
Before 1965, dimes, quarters, and half-dollar US coins contained
90% silver &10% copper.
Since 1965, they are made of a copper (90%) and nickel (10%)
alloy
People started hoarding the silver versions almost as soon as the
new coins began to roll out from the mints.
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$2 quarter?!
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10 oz Pt Bar
12/07/09 @ 11:25 am :
$ 14 31