Material Science

1. Structures of
Materials 1

2. 1.1 Structure of atoms
1. Bohr atomic model, in which electrons are
assumed to revolve around the atomic nucleus in
discrete orbitals, and the position of any
particular electron is more or less well defined
in terms of its orbital.
Atomic Models

3. Electron Configurations
The Aufbau principle
-This principle states that electrons must occupy
available orbitals of lower energy first before orbitals
of higher energy are filled.
Pauli Exclusion Principle
-It stated that only two electrons of opposite spins
can occupy each orbital
Hund rule
-In a given set of orbitals of equivalent energy,
electron tend to occupy the orbitals singly first before
pairing up

4. Question: Write the electronic structure of Na, O,
and Mn.

5. 1.2 Types of bonding & materials
classes
1. Ionic bonding
-found in compounds that are composed of both
metallic and nonmetallic elements, elements that
are situated at the horizontal extremities of the
periodic table.
- Atoms of a metallic element easily give up their
valence electrons to the nonmetallic atoms.
2. Covalent bonding
-stable electron configurations are assumed by
the sharing of electrons between adjacent
atoms.
PRIMARY Bonding

6. 3. Metallic bonding
-the final primary bonding type, is found in
metals and their alloys.
-positive metal ions like Cu+2 or Fe+3 are
surrounded by a "sea of electrons“ or freely-
moving valence electrons valence.

7. SECONDARY Bonding
1. van der Waals bonding
-Secondary bonding forces arise from atomic or
molecular dipoles.
-Dipole interactions occur between induced
dipoles, between induced dipoles and polar
molecules (which have permanent dipoles), and
between polar molecules.
2. Hydrogen bonding
-Special type of secondary bonding, is found to
exist between some molecules that have
hydrogen as one of the constituents.
- A hydrogen atom which is bond covalently to
highly electronegative atom(N, F, O)

8. Atomic Bonding in Solids
 Physical properties of materials is enhanced by a
knowledge of the interatomic forces that bind the
atoms together.
 At large distances, interactions are negligible
because the atoms are too far apart to have an
influence on each other; however, at small
separation distances, each atom exerts forces on
the others.
 These forces are of two types, attractive (FA) and
repulsive (FR), and the magnitude of each depends
on the separation or interatomic distance (r);

9. Atomic Bonding in Solids
 BONDING FORCES  The origin of an attractive force
FA depends on the particular
type of bonding that exists
between the two atoms.
 Repulsive forces arise from
interactions between the
negatively charged electron
clouds for the two atoms and
are important only at small
values of r as the outer electron
shells of the two atoms begin to
overlap.

10. Atomic Bonding in Solids
 BONDING ENERGIES