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METALS

Bonds and Properties

Mr. Shields Regents ChemistryU09 L04

Alloys

Pure Elements

22

Recall that many metals have high luster

Hmmm….

How much is thisshiny Gold worth ??

400 ounces (27.5lbs)$647 / ounce*$258,800 per bar

12 bars =$3,105,600

(* 2007 price)

Standard 400 oz ingots

33

Many Metals have high melting points… But not all!

Where is the High Melting Pt. of W taken advantage of in your home?

44

More Properties of MetalsMore Properties of Metals

LUSTER HIGHHIGH

DEFORMABILITY Malleable & DuctileMalleable & Ductile

CONDUCTIVITY OF

HEAT AND ELECTRICITY

Good to ExcellentGood to Excellent

PHASE at STP Solid (except Hg)Solid (except Hg)

Ion FORMATION Loses eLoses e-- to form to form positive ionspositive ions

IONIZATION ENERGY Low (lowest is Fr)Low (lowest is Fr)

ELECTRONEGATIVITY Low (lowest is Fr)Low (lowest is Fr)

Approx. 78% of theElements in the Periodic Table areMetals

W

55

The bonding in metals is very different from that of an ionic bond

In an ionic bond there is a transfer of electrons from oneatom to another

But in metal bonds electrons ROAM FREELY from one metalatom to the next.

It’s these freely roaming electrons that account for many ofthe properties of metals

Metal bondingMetal bonding

+ -

66Why can electrons in metals roam freely about?

Mobile metal electrons

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Metal bondingMetal bondingMetals exist in organized lattice structures similar to ionicCompounds.

The difference is thatAdjacent atoms in the metalLattice are all the same.

Being in close proximity,Outer Energy levels overlap.

AND…Electrons in the outerValence shell can move freely through these overlappingEnergy levels.

88

Na 3s1 Na 3s1

Overlapping orbitals Valence electrons move fromThe valence shell of one atomto the next

Mobile Metal Electrons

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Metal bondingMetal bonding“Delocalized” electron leaves behind centers of temporarilyPositive Metal Cations.

The delocalized electron thenMoves freely through the Metal from one CationTo the next.

This creates what is called“the Sea of Electrons”

This Sea of Electrons binds each metal Cation to all itsNeighbors.

- A metal bond is the attraction of metallic cations for delocalized electrons

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Metal PropertiesMetal PropertiesIt’s the sea of electronsThat give metals someOf their unique properties.

Because they can move freelyFrom place to place they:

1)Conduct electricity (a flow of electrons)2) Conduct heat3) Are malleable and ductile4) Have luster (e- absorbing then releasing photons at the surface

How do electrons lead to these properties of metals?

1111

Electrical Conductivity

-

Free flow of electrons through the metal

+

e-e-

Flow of electrons

Electrons flow from the metal through the metal wire towards the + charge

Electrons then flow from the negative terminal back into the metal theyoriginally came from.

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Malleability Malleability Metals and non-metals behave very differently when they areHit with a force such as a hammer.

Metals deform andNon-metals shatter.

But Why?

Again it’s a Consequence of The Freely flowingElectrons in metals

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When a force is applied to a metal some of the metal atoms shift away from the force.But the free electrons simply bond the newly overlappingMetal ions together.

The metal has Been deformed butThe shift is notOf any consequence

When a force is Applied to the Non-metal, positiveAnd negative chargesalign. This Results in a fracture due to the force of repulsion

Metal

Non-Metal

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As the number of electrons that can be delocalizedIncreases so does Harness and Strength

Na has one s electron that can be delocalized - its relatively soft & weak ( can be cut with a butter knife)

Mg has two electrons that can be delocalized - so its much harder than sodium but not a lot of strength

Transition metals have several s and d electrons that can bedelocalized

- Chrome is very hard and has high strength

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In General as you move left to right across a periodThe strength and hardness of the metallic bond increases (aslong as the # of s and d electrons that can be delocalized inc.)

(for ex: Fe 2-8-14-2 is harder than Cu 2-8-18-1 because Cu’s d Orbitals are all filled so they are not available for bonding. FeDoes have d orbitals that can participate)

AND In general as you move down a group the strength of theMetallic bond and the hardness decreases because theDelocalized e- are farther from the pos. cation (Cu is a hardermetal than Au)