CAP 1.2 INTERATOMIC BONDS

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Structure of materials
1. atomic structure; 
2. short- and long-range atomic 
arrangements;
3. nanostructure;
4. microstructure; and
5. macrostructure.
We can examine and describe the structure of materials at five different levels:
Materials Science. Professor: José Lázaro
Five different levels Primary Bonds Secondary bonds
Structure of materials
1. atomic structure;
a) The Structure of the Atom.
b) The Electronic Structure of the Atom. These are:
c) The Periodic Table.
d) Atomic Bonding: There are four important mechanisms by 
which atoms are bonded in engineered materials. These are: ✓ metallic bonds;
✓ covalent bonds;
✓ ionic bonds; and
✓ van der Waals bonds.
✓ quantum numbers;
✓ deviations from expected electronic structures;
✓ valence; and
✓ atomic stability and electronegativity.
Materials Science. Professor: José Lázaro
Five different levels Primary Bonds Secondary bonds
Structure of materials
2. short- and long-range atomic arrangements;
Amorphous materials have only short-range atomic arrangements, while 
crystalline materials have short- and long-range atomic arrangements.
✓ In short-range atomic arrangements, the atoms or ions show a particular
order only over relatively short distances (1 to 10 Å).
(Å = 10-10 m y 1nm = 10-9 m).
✓ For crystalline materials, the long-range atomic order is in the form of atoms
or ions arranged in a three-dimensional pattern that repeats over much larger
distances (from ~10 nm to cm.).
Materials Science. Professor: José Lázaro
Five different levels Primary Bonds Secondary bonds
Structure of materials
3. nanostructure;
The nanostructure is the structure of a material at a length scale of 1 to 100 nm. Controlling 
nanostructure is becoming increasingly important for advanced materials engineering applications. 
4. microstructure;
The microstructure is the structure of materials at a length scale of 100 to 100,000 nm or 0.1 to 100 
micrometers (often written as 𝜇m and pronounced as “microns”). 
The microstructure typically refers to features such as the grain size of a crystalline material and others 
related to defects in materials. (A grain is a single crystal in a material composed of many crystals.)
Materials Science. Professor: José Lázaro
Five different levels Primary Bonds Secondary bonds
Structure of materials
5. macrostructure;
Macrostructure is the structure of a material at a macroscopic level where the length scale is >100 𝜇m. 
Features that constitute macrostructure include porosity, surface coatings, and internal and external 
microcracks.
Materials Science. Professor: José Lázaro
Five different levels Primary Bonds Secondary bonds
• When two neutral atoms are brought close to each other, they experience attractive and or repulsive force
• Attractive force is due to electrostatic attraction between electrons of one atom and the nucleus of the other. 
Atomic interaction
Materials Science. Professor: José Lázaro
Five different levels Primary Bonds Secondary bonds
we have two types of bonding: 
1) Primary bonds or Strong bonds between adjacent atoms resulting from the transfer or sharing of outer orbital electrons; and 
2) Secondary bond or Weak bonds, such as van der Waals bonds, that typically join molecules to one another.
Primary bonds or Strong bonds 
✓ metallic bonds;
✓ covalent bonds;
✓ ionic bonds.
Secondary bond or Weak bonds,
✓ Van der Waals bonding;
✓ Hydrogen bonding.
Types of bonding
Materials Science. Professor: José Lázaro
Five different levels Primary Bonds Secondary bonds
Metallic bond 
✓ (electropositive + electropositive). Example: Cu, Na, Hg.
✓ A metallic bond is formed as a result of atoms of low electronegativity elements donating their valence 
electrons and leading to the formation of a “sea” of electrons. 
✓ Metallic bonds are non-directional and relatively strong. As a result, most pure metals show a high Young’s 
modulus and ductility. 
✓ The bonds tend to be no directional. (Compact structure, high density).
✓ They are good conductors of heat and electricity and reflect visible light.
✓ Owing to their electropositive character, many metals such as iron tend to undergo corrosion or oxidation.
✓ In general, the melting points of metals are relatively high.
Many pure metals are good conductors of heat and are effectively used in many heat transfer applications.
Ductility refers to the ability of materials to be stretched or bent permanently without breaking.
Primary Bonds
Materials Science. Professor: José Lázaro
Five different levels Primary Bonds Secondary bonds
Ionic Bonding
✓ The ionic bonding found in many ceramics is produced when an electron is “donated” from one electropositive atom to an
electronegative atom, creating positively charged cations and negatively charged anions.
✓ An electrostatic attraction binds the ions together.
✓ Atoms of a metallic element easily give up their valence electrons to the nonmetallic atoms.
✓ These materials tend to be mechanically strong and hard, but brittle.
✓ Melting points of ionically bonded materials are relatively high.
✓ Bad electrical and thermal conductors (solid state).
✓ The bonds tend to be no directional. (restrictions on the structure, medium to high density).
✓ The atom that contributes the electrons is left with a net positive charge and is called a cation, while the atom that accepts the
electrons acquires a net negative charge and is called an anion.
Example: KF, CaCO3, NaCl.
Primary Bonds
Materials Science. Professor: José Lázaro
Five different levels Primary Bonds Secondary bonds
Ionic Bonding
Atomic numbers
H: 1 (I)
C: 6 (IV)
N: 7 (V)
O: 8 (VI)
Na: 11 (I)
Cl: 17 (VII)
𝑀𝑎𝑥𝑖𝑚𝑢𝑚 𝑛𝑢𝑚𝑏𝑒𝑟 𝑜𝑓 𝑒𝑙𝑒𝑐𝑡𝑟𝑜𝑛𝑠 𝑖𝑛 𝑎𝑛 𝑜𝑟𝑏𝑖𝑡 = 2𝑛2
Primary Bonds
Materials Science. Professor: José Lázaro
Five different levels Primary Bonds Secondary bonds
Covalent bond:
✓ Are characterized by bonds that are formed by sharing of valence electrons among two or more 
atoms. (electronegative + electronegative). 
✓ Covalent bonds are very strong. As a result, covalently bonded materials are very strong and hard.
✓ These materials also exhibit very high melting points, which means they could be useful for high-
temperature applications.
✓ The electrical conductivity of many covalently bonded materials (i.e., silicon, diamond, and many 
ceramics) is not high.
✓ The materials bonded in this manner typically have limited ductility because the bonds tend to be 
directional. (restrictions on the structure, less density).
✓ Is one in which electrons are shared (as opposed to transferred) between atoms in their outermost 
shells to achieve a stable set of eight. (Equation of Lewis).
✓ Example: H2, CH4, H2O. NH3.
Schematic representation of 
covalent bonding in a molecule 
of methane (CH4).
Primary Bonds
Materials Science. Professor: José Lázaro
Five different levels Primary Bonds Secondary bonds
Van der Waals Bonding
✓ Van der Waals bonding between molecules or atoms arise due to weak attraction forces between dipoles
✓ The natural oscillation of atoms leading to momentary break down of charge symmetry can generate temporary 
dipoles
✓ Dipoles can induce dipoles and attraction between opposites ends of the dipoles leads to weak bonding
Hydrogen bonding
✓ Hydrogen bond is a type of secondary bond found in molecules containing hydrogen as a constituent.
✓ The bond originates from electrostatic interaction between hydrogen and another atom of high electronegativity such 
as fluorine or oxygen.
Secondary Bonds
Materials Science. Professor: José Lázaro
Structure Bonding Material Type
Materials Science. Professor: José Lázaro