Solutions Manual for Materials Science and Engineering An Introduction 10th Edition by William Callister| 9781119405498| All Chapters| LATEST

TEST BANK
MATERIALS SCIENCE AND ENGINEERING AN
INTRODUCTION

, CHAPTER 2


ATOMIC STRUCTURE AND INTERATOMIC BONDING


PROBLEM SOLUTIONS




Fundamental Concepts
Electrons In Atoms


2.1 Cite The Difference Between Atomic Mass And Atomic Weight.

Solution

Atomic Mass Is The Mass Of An Individual Atom, Whereas Atomic Weight Is The Average
(Weighted) Of The Atomic Masses Of An Atom's Naturally Occurring Isotopes.
50
2.2 Chromium Has Four Naturally-Occurring Isotopes: 4.34% Of Cr, With An Atomic Weight Of
49.9460 Amu, 83.79% Of Cr, With An Atomic Weight Of 51.9405 Amu, 9.50% Of 53Cr, With An Atomic Weight Of
52


52.9407 Amu, And 2.37% Of 54Cr, With An Atomic Weight Of 53.9389 Amu. On The Basis Of These Data, Confirm
That The Average Atomic Weight Of Cr Is 51.9963 Amu.

Solution

The Average Atomic Weight Of Silicon ( Acr ) Is Computed By Adding Fraction-Of-Occurrence/Atomic

Weight Products For The Three Isotopes. Thus


Acr = f50 A50 + f52 A52  f53 A53  f54 A54
Cr Cr Cr Cr Cr Cr Cr Cr


 (0.0434)(49.9460 Amu) + (0.8379)(51.9405 Amu) + (0.0950)(52.9407 Amu) + (0.0237)(53.9389 Amu) = 51.9963
Amu

, 2.3 (A) How Many Grams Are There In One Amu Of A Material?

(B) Mole, In The Context Of This Book, Is Taken In Units Of Gram-Mole. On This Basis, How Many
Atoms Are There In A Pound-Mole Of A Substance?


Solution

(a) In Order To Determine The Number Of Grams In One Amu Of Material, Appropriate
Manipulation Of The Amu/Atom, G/Mol, And Atom/Mol Relationships Is All That Is Necessary, As

 1 Mol  1 G / Mol 
# G/Amu =  23   




 6.022  10 Atoms 1 Amu / Atom


= 1.66  10-24 G/Amu


(b) Since There Are 453.6 G/Lbm,


1 Lb - Mol = (453.6 G/Lbm) (6.022  10 23 Atoms/G - Mol)


= 2.73  1026 Atoms/Lb-Mol

, 2.4 (A) Cite Two Important Quantum-Mechanical Concepts Associated With The Bohr Model Of The Atom.
(B) Cite Two Important Additional Refinements That Resulted From The Wave-Mechanical Atomic Model.

Solution

(a) Two Important Quantum-Mechanical Concepts Associated With The Bohr Model Of The Atom Are
(1) That Electrons Are Particles Moving In Discrete Orbitals, And (2) Electron Energy Is Quantized Into Shells.
(b) Two Important Refinements Resulting From The Wave-Mechanical Atomic Model Are (1) That
Electron Position Is Described In Terms Of A Probability Distribution, And (2) Electron Energy Is Quantized Into
Both Shells And Subshells--Each Electron Is Characterized By Four Quantum Numbers.