course learning objectives utmnhayati/chapter 1 atomic bonding.pdf · atomic number (# of protons)...

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UTMUNIVERSITI TEKNOLOGI MALAYSIA

1. INTRODUCTION & ATOMIC 1. INTRODUCTION & ATOMIC

STRUCTURESTRUCTURE

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• Introduce the field of Materials Science andEngineering

• Provide introduction to the classification of

materials

• Identify and distinguish between the types ofatomic bonding

COURSE LEARNING OBJECTIVESCOURSE LEARNING OBJECTIVES

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• Historical Overview

• What is Materials Science & Engineering

• Classification of Materials

• Atomic Structure

• Atomic Bonding

CHAPTER OUTLINECHAPTER OUTLINE

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Chapter OutlineChapter Outline

• Stone Age (40,000 to 100,000 yrs ago): Stone tools, clay pots, skin

• Copper Age (5,000 to 10,000 yrs ago): Copper ornaments, earthenware,metal smelting

• Bronze Age (3,000 to 5,000 yrs ago): Bronze (Cu/Sn), glass, iron smelting

• Iron Age (1000 – 3000 yrs ago): Carburized Iron, improved forging, porcelain

• Steel and concrete (100 – 1000 yrs ago)

• Advanced Materials (beginning early 1900s): polymers, ceramics,

composites, semiconductors

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MATERIALSMATERIALS

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MATERIALSMATERIALS

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Properties

ProcessingStructure

Performance

Materials Science

Investigating the relationship between

structure and properties of materials.

Materials Engineering

Designing the structure to achieve

specific properties of materials.

• Processing

• Structure

• Properties

• Performance

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Properties

ProcessingStructure

Performance/ Cost

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Properties Properties

• Properties are the way materials responds to external forces or the environment

� Mechanical

� Electrical and magnetic

� Optical

� Chemical

• To obtain the desired properties the material must have the

appropriate structure

• Processing can produce the appropriate structure

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Properties Properties

Composition, bonding,crystal structure, andmicrostructure definematerials properties

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Classification of MaterialsClassification of Materials

� Metals

� Ceramics

� Polymers: Thermoplastics and Thermosets

� Semiconductors

� Composite Materials

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Classification of MaterialsClassification of Materials

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Engineering MaterialsEngineering Materials

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Functional Classification of

Materials

Functional Classification of

Materials

� Aerospace� Biomedical� Electronic Materials� Energy Technology and Environmental Technology� Magnetic Materials� Photonic or Optical Materials� Smart Materials� Structural Materials

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Atomic StructureAtomic Structure

• Atomic structure is made of:

� Protons: positive (+) charge

� Neutrons: no charge (neutral)

� Electrons: negative (-) charge

• The nucleus contains the mass of an atom: Protons + Neutrons

• Layers of electrons that orbit around the nucleus are called orbitals

or energy-level shells.

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Atomic StructureAtomic Structure

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Periodic Table of ElementsPeriodic Table of ElementsAtomic Number (# of protons)

Atomic weight =

# protons + average # neutrons

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Electronegativity Electronegativity

• Electronegativity is defined as the measure of how willing atoms are to accept electrons

� Subshells with one electron: low electronegativity

� Subshells with one missing electron: high electronegativity

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Periodic Table of ElementsPeriodic Table of Elements

Low electronegativity High electronegativity

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IonsIons

• When an atom loses or gains an electron to or from another atom, it is called an ion

• Types of Ions:

� CATIONS – a loss of electrons: positive (+) charge

� ANIONS – a gain of electrons: negative (-) charge

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Atomic BondingAtomic Bonding

• Atomic bonding is the formation of compounds by combining two

or more elements

• In an atomic bonding electrons are gained, lost or shared

• There are 4 main types of bonding:

� Ionic bonding

� Covalent bonding

� Metallic bonding

� Van der waals

Primary Bonding

Secondary Bonding

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Ionic BondingIonic Bonding

• Ionic bonding occurs

between + and – ions

• Requires electron transfer

between atoms forming

attracting ions

• Example: sodium chloride

(NaCl)

• Other compounds havingionic bonding: MgO, CsCl

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Ionic BondingIonic Bonding

Characteristics of Ionic Bonding

• Ionic compounds are usually hard, rigid and brittle: theresults of ions being held in specific positions

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Covalent BondingCovalent Bonding

• In covalent bonding the electrons are shared between atoms

• Covalent bonds are more stable and stronger than ionic bonds

e.g; Diamond (Carbon)

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Metallic BondingMetallic Bonding

Metallic bonding:

� Valence electrons are detachedfrom atoms, and spread in anelectron sea that glues the ionstogether

+ + + +

+ + + +

+ + + +

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Characteristics of metallic bonding

� Metallic bonds occur between metals

� Good conductors of electricity and heat (due to themobility of electrons)

� Malleability (can be shaped) and Ductility (can bedrawn into wires)

� Brightness and strong light reflection

� Examples: copper (Cu), gold (Au), silver (Ag)

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Secondary BondingSecondary Bonding

• Atomic bonding without electron transfer or sharing

• Arises from interaction between dipoles

asymmetric electron clouds

+ - + -secondary bonding

HH HH

H2 H2

secondary bonding

ex: liquid H2

• Fluctuating dipoles

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• Permanent dipoles-molecule induced

+ - secondary bonding

+ --general case:

-ex: liquid H2O

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-ex: Polymer (PVC)

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Summary: Atomic BondingSummary: Atomic Bonding

• Examples of bonding in materials

� Metals : metallic bonding

Moderate Tm and E

� Ceramics : ionic/covalent

high Tm and high E

� Polymers : covalent and secondary

Small Tm and small E

� Semiconductors: covalent and covalent/ionic

Tm: melting temperature, E: stiffness

course learning objectives utmnhayati/chapter 1 atomic bonding.pdf · atomic number (# of protons)...

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