kinds of metals

1. MODIFICATION
OF
METALS
By : Mark Erick Cezar

2. largest group of elements
METALS

3. Metal + non-metal =
IONIC COMPOUNDS

4. Useful properties that
are not found in any
other materials.

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

7. Why are metals lustrous?
Why do we see a perfect (but
laterally inverted) image in a plane
mirror (silvered glass)?

8. BONDING (microscopic)
STRUCTURE &
names (Symbolic)
PROPERTIES (macroscopic)

9. METALS
STRUCTURE
defines the
PROPERTIES
but
MODIFYING METALS

10. Larger in diameter,
so low/high electronegativity
Tend to lose/gain e-
Become cations/anions
More stable

11. Metal elements have: 1, 2 or 3 valence electrons.
E.g. Magnesium 12: 2,8,2
To be stable they lose this last electron and become positively charged according
to how many they lose
N
O
F
Ne
Na
12p+
Mg 2+

12. 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).

13. Mg2+
Mg2+
Mg2+
Mg2+ Mg2+
Mg2+
Mg2+ Mg2+
Mg2+

14. • 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

15. 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)

17. PROPERTIES

18. PROPERTIES
EXPLAINED BY THE
STRUCTURE

19. E- can absorb quantum of energy and become excited
When 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

20. 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

21. WHAT IS HAPPENING?
(discuss)
Good conductor of heat
2

22. 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

23. Note: flow of current is the flow of positive charge, i.e.
opposite direction of electron flow
WHAT IS HAPPENING?
(discuss)
3

24. Note: flow of current is the flow of positive charge, i.e.
opposite direction of electron flow
Current = flow of charge
Sea of electrons = free to move
3

25. WHAT IS HAPPENING?
(discuss)
4

26. Explains malleableand ductilenature 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

27. High melting and boiling point
To 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

28. 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 temperatures
Generally have high densities
High tensile strength – hard and tough and offer high
resistance to the stresses of being stretched or drawn
out and therefore do not easily break.

29. 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)

31. 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

32. MODIFYING METALS
1. Work hardening
2. Heat treatment
3. Alloying

33. 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?

34. 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.

35. 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

36. 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.

37. 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.