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PRESENT BY: JON AFFI, MT, Dr. Eng GUNAWARMAN, Dr.-Ing HAIRUL ABRALMETALLURGY LABORATORY- MECHANICAL ENGINEERING-ANDALAS UNIVERSITY 2005

ENGINEERING MATERIAL HANDOUT

Minggu 2. Struktur dan Ikatan atom

a. Struktur Atom dan Konsep Dasar Model Atomb. Konfigurasi Elektron dan Tabel Priodik Atom-

atomc. Ikatan Atom Zat Padatd. Ikatan Ione. Ikatan Kovalenf. Ikatan Logam



AtomMerupakan bagian terkecil dari unsur yang menentukan jenis dari material karena sifatnya.

3 subatomic particle:

a.Protonsb.Neutronsc.Electrons



Model atomSampai sekarang masih dianggab atom sebagai inti yang sangat kecil (Ф10-14m) yang dikelilingi awan electron sehinggadiameter atom menjadi 10-10mInti terdiri dari proton dan neutron



Massa dan muatan subatom

Particle Massa (grams) Muatan (coulombs)

Proton 1.673x10-24 +1.602x10-19

Neutron 1.675x10-24 0

Electron 9.109x10-28 -1.602x10-19



Nomor Atom / ZAdalah jumlah proton dalam atom dan jugamenunjukkan jumlah electron dalam keadaan netral. Setiap unsur berbeda nomor atom dengan karakteristikberbeda pula.

Massa Atom /AAdalah jumlah proton dan netron dalam atom

Massa Atom relatifAdalah massa dari elemen dengan jumlah atom 6,023 x 1023. (Bilangan Avogadro).



Atom carbon mempunyai 6 proton dan 6 neutron dipakai sebagai acuan untukmassa atom.1 amu /atomic mass unit didefinisikansebagai 1/12 massa atom carbon yang mempunyai massa 12 unit.



Atomic Illustrations



Perpindahan tingkat energi electron mengelilingi atom memancarkan radiasi electromagnetic yang disebut photon. Perubahan energi ΔE nya didefinisikan oleh persamaanPlanck’s

ΔE = h.νh = konstanta planck’s 6,63 x 10 -34 J.sc = λ.ν = 3.00 x 10 8 m atau kecepatan cahayaλ = Panjang gelombang

SehinggaΔE = h.c/ λ dalam satuan eV /electron Volt



Electron emisi atau absorbsi

Pustaka: Principle Material Science and Engineering by William F Smith



Tabel Priodik

Pustaka: Principle Material Science and Engineering by William F Smith



Ionization Energy of Hydrogen Electron



Orbit elektron mengelilingi atom sangat komplek. Bisa berbentuk bulat, ellips. Sehingga posisi elektron secara pasti sulit ditentukan. Penggambaran paling mudah tentang posisi elektron adalah sebagaiawan elektron yang menyelubungi inti atom. Jari-jari r dianggab sebagaiposisi elektron paling mungkin. r = 0.05 nm



Quantum Numbers

1. Principle Quantum Numbers / n = 1 to 7 2. Subsidiary Quantum Numbers / l = 0,1,2,3

or s,p,d,f3. The Magnetic Quantum Numbers ml = -l to

+l and 04. Electron Spin Quantum Numbers +1/2 and

-1/2



Electron Configuration in Atom



Maximum Number of electron for each principle atomic shell (Pauli Principle = 2n2)ex: 2 for 1st PQN, 8 for 2nd PQN, 18 for 3th

PQN, and for next 32, 50, 72, 98.


ENGINEERING MATERIAL HANDOUTRelative Atomic Radii in nm



Noble GasThe Most Stable and Least Reactive of All Element are The Noble GasThe exception of Helium with has a 1s2 electron configuration, the outermost shell of all the other noble gas (Ne, Ar, Kr, Xe and Rn) has an s2p6 electron configuration (Inactive / stable configuration).Electropositive and Electronegative ElementsElectropositive element are metallic in nature and give up electrons in chemical reaction to produce positive ion / cations. The number of electrons give up Positive Oxidation number. Group 1A and 2A in Priodic tableElectronegative element are nonmetallic in nature and accept electrons in chemical reaction to produce negative ion / Anion. The number of electrons give up Positive Oxidation number. Group 6A and 7A in Priodic tableSome elements of group 4A to 7A have dual behavior C, Si, Gr, P etcFigure 2.8 shows oxidation number of elements



Oxidation Number of Element


ENGINEERING MATERIAL HANDOUTElectronegativityThe Degree of an atom to attract electron to itselfScale from 0 to 4.1The electropositive elements have low electronegativity degreeThe electronegative elements have high electronegativity degree



Atomic BondingChemical bonding between atoms occurs since

there is a net decrease in the potential energy of atom in the bonded state. Atom in bonded state more stable energy than when it are unbonded

Two group of atomic bonding:1. Primary atomic bonds / strong bonds

Ionic Bonds, Covalent Bonds, Metallic Bonds

2. Secondary Bonds / weak bondsPermanent Dipole Bonds, Fluctuating Dipole Bonds


ENGINEERING MATERIAL HANDOUTIonic Bonds

Form between highly electropositive or metallic and highly electronegative elements or non metallic. The atoms convert to ion with reduce or increase atomic radius.



Interionic forcea. Attractive forceb. Repulsive forceThe equilibrium occur if attractive force equal to repulsive force with

distance ao

Fnet = Fatt + F rep

Fatt = -(Z1 Z2 e2)/(4π Єo a2)Z1 Z2 Number electron removed or addede Electron chargea Interionic Separation distanceЄo Permittivity of free space 8.85 X 10-12 C2/(N.m2)

F rep = - n b/ an+1

b and n are constant



Interionic Force



Interionic Energy



Covalent BondsForm between low electropositive and low electronegative elements. The Atoms share their outer s and p electron with other atoms so that each atom attains the noble-gas electron configuration

Covalent bonding of Hydrogen Covalent bonding of Others



Covalent Bond Energies and Lengths



Covalent Bonded Molecule example



Metallic Bonds

A third primary type of atomic bonding is metallic bonding which occurs in solid metal. The atoms are packed relatively close together in a systematic pattern or Crystalline. The atoms are so close together so the outer valence electron are attracted to numerous neighbors. This condition forms the low density electron charge cloud or electron gas. The electron are weakly bonded to positive ion core and easy to move. It is called free electron and support for high thermal and electric conductivity of the metal



Metallic bonds



Bond energy equilibrium for metal

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