largest group of elements

METALS

Metal + non-metal =

IONIC COMPOUNDS

Stable?

No

Gain e-

Give e-

Share e-

IONIC COMPOUND

Metal + Non-metalMetallic Lattice

Metal

Useful properties that are not found in any other materials.

Metals are used where strength of a material is an important factor.

Why are metals lustrous? Why do we see a perfect (but

laterally inverted) image in a plane mirror (silvered glass)?

BONDING (microscopic)

STRUCTURE &

names (Symbolic)

PROPERTIES (macroscopic)

METALS

STRUCTUREdefines the

PROPERTIESbut

MODIFYING METALS

Larger in diameter,

so low/high electronegativity

Tend to lose/gain e-

Become cations/anions

More stable

Metal elements have: 1, 2 or 3 valence electrons.E.g. Magnesium 12: 2,8,2To be stable they lose this last electron and become positively charged according to how many they lose

NOFNeNa

12p+Mg 2+

Since metal atoms have low electronegativities and they want to be more stable, the outer shell/ valence electron jumps out. These delocalised e-s form the pool/sea of delocalised e-s. (note: the language of pool/sea).

Mg2+Mg2+Mg2+

Mg2+ Mg2+Mg2+

Mg2+ Mg2+Mg2+

• Figure 5.5 A sodium metal lattice. Each sodium atom provides its one valence electron to form a ‘sea’ of delocalised electrons.

Metallic bonding =

electrostatic attraction between…

… positive cations and delocalised electrons

YOU DRAW

Mg+ Mg+ Mg+ Mg+

Mg+ Mg+ Mg+ Mg+

Mg+ Mg+ Mg+ Mg+

METAL LATTICE

Electrostatic attraction between

CATIONS & Delocalised e- (sea of e-) (e-s free to move)

PROPERTIES

PROPERTIES

EXPLAINED BY THE STRUCTURE

E- can absorb quantum of energy and become excitedWhen they fall back they release it as light

Metal lattice contains‘Free’ e- = almost all differences of energy levels can be absorbed and re-emitted

= almost all visible light reflected. = Lustrous (shiny)

1

Every electron can absorb a specific quantum or packet of radiation to become excited . "Free" electrons often absorb quanta of visible light.

In metals the outer electrons are essentially "free" electrons and their energy depends on their distance from a nucleus; as there are countless "free" electrons of almost every possible extranuclear distance and energy they can absorb all the visible light that falls on the metal surface.

However an excited electron re-emits the same absorbed quantum of radiation as it becomes de-excited and most of the radiation that is incident on a metal surface is expelled from the surface thus:

metals are highly reflective or lustrous.

1

WHAT IS HAPPENING?(discuss)

Good conductor of heat

2

Good conductor of heat

• When atoms absorb heat energy they vibrate (temperature is a measurement of molecular energy) and this vibration is passed from one atom to the next.

• In metals, because the metal atoms are often close packed together the vibration or heating effect is passed rapidly through the metal from one atom to another. Also electrons are free to move so will bump and transmit this energy rapidly.

2

Note: flow of current is the flow of positive charge, i.e. opposite direction of electron flow

WHAT IS HAPPENING?(discuss)

3

Note: flow of current is the flow of positive charge, i.e. opposite direction of electron flow

Current = flow of chargeSea of electrons = free to move

3

WHAT IS HAPPENING?(discuss)

4

Explains malleable and ductile nature of metals.

Ionic Lattice

Electrostatic attraction b/w cations and anions broken

Metallic Lattice

Electrostatic attraction b/w cations and sea of electrons still present after deformation.

4

High melting and boiling pointTo break the lattice the bonds must be broken. The electrostatic force between the sea of electrons and the cations is very strong. Thus it requires lots of energy, therefore it has high melting point and it is hard. (note: the more delocalised electrons the stronger these properties)

The cations and electrons are closely packed together b/c strong…High density

5

Limitations of structure/propertiesExamples of some exceptions

Mercury (low m.p.)

Co, Ni, Fe (magnetism)

Chronium (brittle)

Properties (GENERALLY)

Lustrous (Shiny when freshly cut or polished)Good conductors of heat Good conductors of electricity Malleable (can be shaped by heating) and Ductile (can be drawn into a wire)Generally have high melting and boiling temperaturesGenerally have high densitiesHigh tensile strength – hard and tough and offer high resistance to the stresses of being stretched or drawn out and therefore do not easily break.

Ball bearing model

• Strength depends on arrangements of atoms in their crystal grains

• Metals with rows in lattice distorted do not bend as easily. (rows do not slide as smoothly)

Grain: areas of perfect close-packing of cations

• Grain: areas of perfect close-packing.

• Grain boundaries: boundaries b/w grains.

• Grains are irregular shaped crystals of the metal pushed tightly together.

Small grain

Many dislocations and they do not bend easily = hard

less malleable = brittle

Large grains

Have fewer dislocations and they bend easily

malleable

MODIFYING METALS

1. Work hardening

2. Heat treatment

3. Alloying

Work hardening

Bending or hammering cold metals

Crystal grains become smaller

• Metal is tougher (work hardened)

• More brittle (e.g. keep bending a metal wire, it goes harder, then it snaps.)

Bend a wire. What happens?

Heat treatment

Annealed Heated to red hot, cooled slowly

Larger crystals

Softer (restores ductility)

Quenched Heated to red hot,

Cooled quickly (in cold water)

Smaller crystals

Harder but more brittle (e.g. horseshoes)

Tempered Quenched, warmed again to a lower temperature, cool slowly.

Consistent small crystals

Retains hardness, reduce brittleness.

Alloying

Combining a metal with other metals or some non-metals (Through melting and cooling the mixture)

Achieve alloy that has properties different from pure metals – eg. Silver alloy is harder than silver, Solder

(Pb and Sn) has lower melting temp. than Pb and Sn

Ni-Cu alloy

Magnetic alloys are at the heart of a wide range of technological applications from the oldest of structural materials to the next generation of data storage and retrieval devices.

Two types of alloys:

• Substitutional: atoms of metals are about the same size and replace each other in metal crystal

• Interstitial: atoms of different size. Smaller atoms fit into the spaces between the larger atoms.