1. Chemical Bonds - (Metallic Bonding)
Properties of many materials can be understood in terms of their microscopic properties:
connectivity between atoms,
three dimensional shape of the molecule.
Atoms that are strongly attracted to one another form a chemical bond
What causes this attraction between atoms?

2. Electrostatic Forces
Electrostatic Force – attraction and repulsion (between positive & negative charges) determines the type of bonding between atoms.
The type of bond (Ionic, Metallic, Covalent…) is determined by the form of electrostatic forces between different types of atoms.
Ionic = Pos. Cation & Neg. Anion
Metallic = Pos. Cation & Neg. Electrons & Pos. Cation
Covalent = Non-metal & (Neg. electrons) & Non-metal (neutral) (neutral)

3. Ionic Bonds (transfer of electrons)
Pos Cation
Neg Anion
Electrostatic Force
Crystal Lattice (Repeating Pattern)

4. Metallic Bonds Form between two or more metals
Metallic bonds - the attractive forces between metal cations (+) and the SHARED “Sea” of freely moving valence electrons (-) of the metal.
Atoms of metals achieve stability by sharing their Delocalized valence electrons. (Sea of Ve-)

5. “Positive metal cations ions in a sea of mobile valence electrons.”
Metallic Bonds
“Positive metal cations ions in a sea of mobile valence electrons.”
                                                                                                                                                                                        
Delocalized Valence Electrons

6. Properties of Metals ~ good conductors of electricity
…Electric current = flow of charge.
…Electrons have a negative charge.
Metals are good conductors of electricity because, the “sea” of negatively charged electrons are already moving and these electrons can easily flow in a specific direction
(when a voltage potential is applied – DC battery or AC wall outlet).

7. Properties of Metals ~ good conductors of HEAT
Metals are good conductors of HEAT because, the Delocalized mobile electrons are constantly moving which allows the positive cations to be more easily moved (or repositioned).
Metals have mobile electrons and the cations are more easily moveable. Greater vibration movement of cations.
Ionic solids do not have moving electrons, so the alternating cations & anions are more “LOCKED” in place. Lesser vibration movement.

8. Conduction
When you heat a metal strip at one end, the heat travels to the other end.
As you heat the metal, the particles vibrate, these vibrations make the adjacent particles vibrate, and so on and so on, the vibrations are passed along the metal and so is the heat. We call this?
Conduction

9. Within an object (adjacent particles)
CONDUCTION:
Conduction: The transfer of heat from one particle of matter to another by direct particle to particle contact.
Conduction occurs primarily in solids because the particles are tightly packed together.
The particles themselves DO NOT change positions. (They vibrate in place)
Within an object (adjacent particles)
Solid A

10. Touching/Contact between objects
CONDUCTION:
Conduction: The transfer of heat from one particle of matter to another by direct particle to particle contact.
Conduction occurs primarily in solids because the particles are tightly packed together.
The particles themselves DO NOT change positions. (They vibrate in place)
Touching/Contact between objects
Solid B
Solid A

11. Properties of Metals ~ are Malleable & Ductile
…malleable - able to be beaten into a shape …ductile - able to be drawn into a wire
Metals are good Malleable & Ductile because, the mobile electrons are constantly moving which allows the positive cations to be more easily moved (or repositioned).
Both malleability and ductility ared explained in terms of the mobility of the valence electrons

12. Metals are Malleable +
Force

13. Metals are Malleable + + + + Force + + + + + + + +
Mobile electrons allow atoms to slide by, sort of like ball bearings in oil. + + + +
Force + + + + + + + +

14. Ionic solids are brittle
Force + -

15. Ionic solids are brittle
Strong Repulsion breaks a crystal apart, due to similar ions being next to each other. + -
Force + - + - + -

16. Due to the mobility of the valence electrons, metals have:
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Due to the mobility of the valence electrons, metals have:
Notice that the ionic crystal breaks due to ion repulsion!
1) Ductility
2) Malleability
and

17. Properties of Metals
Metal possesses a number of particular characteristics. Metal substances:
~are good conductors of electricity ~are good conductors of heat ~are malleable (able to be beaten into a shape) ~are ductile (able to be drawn into a wire)
~have lustre (shine) ~are solid at room temperature, with high melting points ~have a high density

19. Metals Form Alloys
One type of metal atom (copper) does NOT BOND with another type of metal atom (zinc). These type different types of atom form ALLOYS.
Alloy – a mixture (solution) of a metal in a metal.

20. Alloys We use lots of metals every day, but few are pure metals.
Alloys are mixtures of 2 or more elements, at least 1 is a metal. Made by melting a mixture of the ingredients, then cooling
Brass: an alloy of Cu and Zn
Bronze: an alloy Cu and Sn
18 k Gold: an alloy of Au, Ag, and Cu
12 k Gold: an alloy of less Au and more Cu

21. Composition of Selected Alloys
Stainless Steel
74% Fe, 18% Cr, 8% Ni, 0.18% c
Coinage Silver
90% Ag, 10% Cu
Plumber’s Soder
67% Pb, 33% Sn
Brass
67% Cu, 33% Zn
18 Carat Gold
75% Au, 10-20% Ag, 5-15% Cu
Nichrome
60% Ni, 40% Cr

22. Why use alloys?
Properties of alloys are often superior to the pure metal element.
Sterling silver (92.5% Ag & 7.5% Cu) is harder and more durable than pure Ag, but still soft enough to make jewelry and tableware
Steels are very important alloys
corrosion resistant, ductility, hardness, toughness, cost

23. More about Alloys…Types???
a) substitutional alloy- the atoms in the components are about the same size
b) interstitial alloy- the atomic sizes quite different; smaller atoms fit into the spaces between larger
Amalgam- (dental use), is an alloy containing Hg with some other metal.