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Sebuah persentase besar dari material mesin menggunakan elemen dalam bentuk gabungan , dalam

penggambungan ( sebuah gabungan besi denan satu atau lebih elemen lain )

Dalam bahan kimia gabungan elemen dengan ukuran yang pasti dari komponen elemen) dan pada

sebuah perbadnigan kecil , dalam campuran ( sebuah reaksi fisika gabungan dari dua zat atau lebih .

Perbedaan di antara sebuah campuran dan sebuah gabungan pada dalam campuran dari elemen yang di

tambahkan pada logam murni , dan bisa menjadi solusi untuk memadatkan .

Atom ini bisa menempatkan posisi di struktru Kristal , komponen pada sebuah campuran tidaklah

normal pada solusi kepadatan . sebuah penyatuan adalah sebuah campuran dari partikel yang pada [ada

sebuah cairan .tidak ada sebuah ikatan diantara cairan dan partikel , gabungan dari elemen menjadi gas

, padat , ataupun cair .. pembahasan ini akan terkonsentrasi pada kombinasi untuk membuat material

yang padat.

Beberaapa pengerasan ialah bentuk pencampuran dari reaksi kimia , dan bagian yang paling kecil dari

sebuah pencampuran masih tertahan oleh sifat dari pencampuran molekul . biasanya molekul berisibermacam macam atom dengan perbandingan satu atom dengan yang lain ,

H2O _ adalah sebuah molekul air penggabungan dari 2 atom hydrogen dan 1 atom oksigen.

Gas sering berbentuk molekul seperti dengan atom :

H2 _ sebuah molekul dari gas hydrogen yang tersusun dari 2 atom hydrogen .

Tulisan bergasris merupakan nilai dari atom dalam pencampuran reaksi atau reaksi sejenis , ketika lebih

dari satu molekul pada zat yang melibatkan diri pada reaksi kimia . sebuah awalan yang biasanya

menunjukkan nilai ini :

4H2O _ 4 molekul dari air

Rekasi kimia dituliskan dengan menggunakan persaamaan menggunaakan sistem symbol ini :

H2O >> H2 + O __ sebuah formula untuk merinci kan air kedalam bagian komponen , hydrogen dan

oxygen .

Pada kenyataan praktek itu telah diketahui bahwa peruraian dari produksi air dwiatom ( 2 dari atom

yang sama dalam sebuah molekul ) hydrogen dan oxygen . selanjutnya persamaan menjadi simaban

untuk menghsilkan nilai ini :

2H2O >> 2H2 ^ + o2 ^ (gas )

Semua reaksi kimi menjadi seimbang , nilai dari atom pada reaksi sejenis harus menghasilkan nilai dari

atom pada reaksi produk.

Beberapa hukum dari reaksi kimia dan fisika memperhatikan keterikatan zat dan kecenderungan dari

keterikatan ,

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Sebuah aturan biasa

In the bottom left corner in the boxes of the periode table . (see electron shells figure 2-2

Quantum numbers and quantum mechanics are of limited significance to the material user , but these

designations are sometimes used ini chemmical analysis techiniques , some instruments that break

down compounds into atoms for chemical analysisi make identifications by referring to peaks for 2s or

2[ electyons anad similar quantum mechanics designations . it is probably sufficient for materials users

simply to be aware that the makeup of atoms is important In determining reactivity in forming usable

compounds , and it is the makeup of atoms that determines their engineering properties .quantum

mechanics is the current systems for designating the component parts of atoms and these atoms are the

building blocks for engineering materials.

2.2 the periodic table

The properties of elements tend to be a periodic function of their atomic numbers,it is common practice

to list the elements in the array shown in figure 2-2 , the periodic table . the atomic number od theelement increases horizontally in the table , and the vertical groupings are based in similarities in

valence electron configurations and similarities in chemical and physical proeperties od the ekements .

the elements in group 1 are called alkali metals : group 2 elemenrs are alkaline earth metals . the groups

listed as transitions elements are metals with a particular ekecetron subshell configuration (incomplete

subshell ) . Groups 13, 14, 15, 16, and 17 are mostly non merals ( as shown by the heavy line ) and the

lemenet in the last vertical grouping are inert gases the groups of element in the separate horizontal

blocks lanthanide series an actinide series really belong in periods 6 and 7 respectively but to list them in

this way would make the table unbalanced in shape . the elements in each series behave the same

chemically thus , this deviation is logical as well as practical.

The periodeic table was developed in the mid nineteenth century by chemists who were trying to

arrange the elements known at that time by similarities in chemical behavior . a Russian scientist , D.I

Mendeleev has been accepted as the author of the table , which looks generally like the one in use

today . the horizontal rows are the periods , they star from the left and aeach element (going right) has

done more charges are neutralized by an additional electron the period ends with a noble gas with eight

electrons in its valence ( outer) shell . there is a periodic variation In atomic configuration based in which

electron shell is being filled . it is this periodic variation In electron configuration that leads to periodic

property variations . elements in a particular vertical group all have the same number of electrons in

their valence shell (with some exceptions ) and this is thought to be the reason why they have the same

general chemical behavior . the noble (inert) gases have similarities in properties , the elements in group17 called halogens have chemical similarities and so on for each group.

Elements in the periodic table with an atomic number greater than 92 do not exist in nature they were

produced by nuclear reactions , there is no definite end to the periodic table . elements with atomic

number as high as 140 have been identified but they are relativeky unstable and some are even

unnamed .

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What is the significance of the periodic table in engineering materials ? foremost , it is the dictionary for

the names and chemical symbols of the elements that are the building blocks for all engineering

materials . the chemical symbols for the elements are used troughout subsequent discussions of

materials and their processing . the family groupings indicate which element behave similarly . this can

sometimes be an aid in selection problems . the atomic weight is the average weight of the common

isotopes of a particular element. The atomic weight is an indicator of the density of an element . a

physical property that can also enter into selection . the simplified electron structure shown in figure 2-3

shows the number of electrons in the various orbitals. the number at tge far right is the number of

electron in the valence shell . this number and the element grouping provide indicators of how a

particular element might combine with other elements,

2.3 forming engineering materials from the elements

Some of the elements are used as engineering materials in their pure element state . many metals fall

into this category beryllium titanium copper gold silver platinum lead mercury and many of the re

fractory metals (W , Ta , Mo , Hf ) are used to make industrial items. Many metals are used in the pure

state for electroplating durable goods , tools , electrical devices : Cr , Ni , Cd , Sn , Zn , Os ,Re , Rh. In the

non metal category , carbon is used in dustrial applications for motor brushes and wear parts , and in

the cubic form as diamond for tools . the inert gases are other nonmetals that are used in the elemental

(ions or molecules ) form for industrial applications for protective atmospheres and the like . table 2-1

presents some property information on elements that are commonly used in the field of engineering

materials.

HALAMAN 21

6. when atoms interactfor example to form compoundselectrons go into unoccupied orbitals rather

than into a partially occupied orbital

7. the outermost , or valence , electrons largerly determine the chemical behavior of elements . the

maximum number is eight.

8. in chemical reactions , most elements attempt to attain an electron structure of eight electrons in the

outermost energy kevel. This is the most stable configuration.

The term quantum is used in physics to describe the amount of energy that is given off when an electron

moves from one orbit to a lower orbit. Quantum mechanics and quantum numbers deal with electron

configurations and things that happen when these electrons and atomic particles are manipulated in

atomic reactions . the difference between the Bohr atom and the quantum mechanic atom is illustrated

in figure 2-5 . the bohr atom model of the element oxygen shows that some of the electrons are paired

in the two orbitals. The paired electrons are in sublevel of an orbit. The orbitals are designated by

numbers from 1 to 7 , and these numbers are called the principal quantum numbers . the subleves in

each orbital (principal quantum number ) are identified by letters , the sublevel with the lowest energy

state is called the S sublevel , the next is the P sublevel , and then there is a D and an F sublevel . if there

are two electrons in the S sublevel of the second orbital . this is designated as 2s2 . there is a quantum

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number designation for each element . for example , the configurations of carbon is 1s22s2p2 , the

configuration of the elements using the old Bohr atim notation is shown.