Lecture 02 - Bonding and crystal structure

# Lecture 02 - Bonding and crystal structure - MATE1412:...

This preview shows pages 1–13. Sign up to view the full content.

MATE1412 2011 MATE1412: Materials Engineering I Lecture 2 Callister : 8 th Ed -Chapter 2, pages 28-39, & Chapter 3, pages 46-55, 72-73 Prof. Tim Sercombe Room : 2.12 Phone : 6488 3124 email :: tim.sercombe@uwa.edu.au

This preview has intentionally blurred sections. Sign up to view the full version.

View Full Document
MATE1412 2011 Reminders • Tutorials start next week, Labs in Week 3 • Closed in shoes are required for ALL labs. • Use OLCR to sign up for labs • Text book: can buy text and WileyPlus access code at a discount • Can also purchase online text through Wiley Plus • All relevant information on unit website ( http://www.mech.uwa.edu.au/unit/MATE1412/ ).
MATE1412 2011 Learning Objectives At the end of this lecture you should be able to: – Understand the factors that promotes bonding – Recognise difference between the types of bonding – Infer material properties from the type of bonding – Understand how atoms assemble into solid structures (for now, focused on metals) – Understand how the density of a material depends on its structure – Calculate the theoretical density of an element – Understand the difference between a single crystal and polycrystalline material

This preview has intentionally blurred sections. Sign up to view the full version.

View Full Document
MATE1412 2011 Bonding Forces and Energies • Many physical properties are determined by the interatomic forces that bind two atoms together. • Consider the simple case of bringing 2 atoms close to each other.
As gap decreases, attractive forces dominate At some point electron shells overlap => repulsive forces At large separations, negligible forces exerted At equilibrium, the attractive force, F A equals the repulsive force, F R

This preview has intentionally blurred sections. Sign up to view the full version.

View Full Document
Bonding Force Equilibrium point, r O , typically ~3Å = 3x10 -10 m Adapted from Fig. 2.8(a), Callister and Rethwisch 8e.
Bonding Energy Bonding energy , E O , is the energy required to separate the two atoms to infinite distance Equilibrium point Adapted from Fig. 2.8(b), Callister and Rethwisch 8e.

This preview has intentionally blurred sections. Sign up to view the full version.

View Full Document
Bonding Energy and Properties • Materials with a high bonding energy have a: High or low melting point? Elements Bonding Energy (kJ/mol) Melting Point (ºC) Hg 68 -38 Al 324 660 Fe 406 1538 W 849 3410 C 713 ~4440
MATE1412 2011 Bonding Energy and Properties • At room temperature : – Solids have high bonding energy (eg Al 324kJ/mol) – Liquids intermediate bonding energy, (eg Hg 68kJ/mol) – Gases low bonding energy (eg Ar 7.7kJ/mol). • Also can determine – Stiffness – Thermal expansion co-efficient – Strength

This preview has intentionally blurred sections. Sign up to view the full version.

View Full Document
MATE1412 2011 Primary Interatomic Bonds • Three types – Ionic – Covalent – Metallic • Nature of bond depends on electron structure of the atoms (ie. the valence e - ) • Atoms are more stable with full outermost electron shell (like noble gases) and will give or take e - to get there.
MATE1412 2011 Ionic bond metal + nonmetal donates accepts electrons electrons Dissimilar electronegativities ex: Mg O Mg 1 s 2 2 s 2 2 p 6 3 s 2 O 1 s 2 2 s 2 2 p 4 [Ne] 3 s 2 Mg 2+ 1 s 2 2 s 2 2 p 6 O 2- 1 s 2 2 s 2 2 p 6 [Ne] [Ne]

This preview has intentionally blurred sections. Sign up to view the full version.

View Full Document
MATE1412 2011 Ionic Bonding • Occurs between + and - ions. • Requires
This is the end of the preview. Sign up to access the rest of the document.

## This note was uploaded on 09/06/2011 for the course ENGINEERIN 1 taught by Professor Tim during the Spring '11 term at American University of Kuwait.

### Page1 / 46

Lecture 02 - Bonding and crystal structure - MATE1412:...

This preview shows document pages 1 - 13. Sign up to view the full document.

View Full Document
Ask a homework question - tutors are online