Download STRUCTURE OF MATERIALS Three types of atomic bonds

STRUCTURE OF
MATERIALS
Three types of atomic bonds:



Covalent bonds
Ionic bonds
Metallic bonds
Covalent bonds
Known as primary
bonding.
A pair of atoms are
Shared by two or more
atoms.
Ionic bonds
Cations (+) and
anions (-) are attracted
to each other in an ionic
bond.
Electrons may be
transferred from one
atom to another in
ionisation.
Metallic bond
Cations in a ‘sea’ of
electrons.
The movement of these
electrons makes metals
good conductors of heat
and electricity.
Properties of metals







Conduct heat and electricity
Malleable and ductile
Electron donors (form oxides)
Can take a shine
High density
High tensile strength
Solid at room temperature (except Mercury)
Crystalline structures



Body-centred cubic (BCC)
Face-centred cubic (FCC)
Close-packed hexagonal (CPH)
Slip in BCC and FCC
structures
As atoms in FCC are more closely packed than
BCC, slip will occur more easily. FCC metals are
ductile and BCC metals are more brittle.
Crystal defects
There are two categories of defects in a crystal
 Line defects – dislocations.
 Point defects vacancy
substitution
interstitial
Vacancy point defect
Substitution point defect
Interstitial point defect