02 Atomic Structure 2012

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Atomicstructure

Jurusan Teknik Mesin dan IndustriFak Teknik UGM

2012/2013


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The Atomic Theory of MatterAtom atomos (Greek) = indivisible

Democritus (460-370 BC)

Daltons atomic theory of 1803:.

particles called atoms2. All atoms of a given element are identical3. Atoms of an element are not changed into different

types of atoms by chemical reactions4. Compounds are formed when atoms of more than

one element combine


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The Atomic Theory of Matter

Theories of chemical combinations:

The law of constant composition(Constant number & kinds of atom in a compound)

(Constant mass before & after reaction)

Dalton used these "laws" to derive another

"law" - the law of multiple proportions(The ratios of the relative masses of each element ina compound = a small whole number)


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The Discovery of Atomic

Structure

1803 Dalton - the atom is a indivisible,

indestructible, tiny ball 1850 Evidence is accumulating that the

particles


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The Discovery of Atomic Structure

Behavior of moving charge in magnetic field


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Cathode rays and electrons

The "rays" traveled towards, or were attracted to thepositive electrode (anode)

Not directly visible but could be detected by their ability

to cause other materials to glow, or fluoresce Traveled in a straight line Their path could be "bent" by the influence of magnetic

A metal plate in the path of the "cathode rays" aquired anegative charge

The "cathode rays" produced by cathodes of different

materials appeared to have the same properties

The cathode ray radiation was composed of negativelycharged particles (electron)


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J.J. Thompson (1897) measuredthe charge to mass ratio for astream of electrons at 1.76 x108 coulombs/gram.


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Robert Millikan (1909) was able to successfully

measure the charge on a singleelectron (the"Milliken oil drop experiment"). This value wasdetermined to be 1.60 x 10-19 coulombs.

,determined to be:(1 gram/1.76 x 108 coulombs)*(1.60 x 10-19coulombs) = 9.10 x 10-28 grams

Note: the currently accepted value for the massof the electron is 9.10939 x 10-28 grams.


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Radioactivity Wilhelm Roentgen (1895) discovered the "x" ray

They could pass unimpeded through many objects They were unaffected by magnetic or electric fields They produced an image on photographic plates (i.e.

they interacted with silver emulsions like visible light) Henri Becquerel (1896)

Uranium radioactivity

Marie and Pierre Curie Isolate the radioactive components in the uranium

mineral.


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Radioactivity

Ernest Rutherford studied alpha rays, beta rays

and gamma rays, emitted by certain radioactivesubstances.


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The nuclear atom

(1900) (1910)


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The nuclear atom

Rutherford (1919) discovers protons - positively

charged particles in the nucleus Chadwick (1932) discovers neutron - neutral

charge particles in the nucleus


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The Modern View of Atomic

Structure

Sub atomic particle:

ElectronNegatively charged (-1.602 x 10-19 Coulombs

- . Proton

The proton has a charge of +1 electron

charge (+1.602 x 10-19

C) NeutronsElectrically neutral.


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The Modern View of Atomic Structure

An atomic mass unit (amu) is equal to 1.66054 x 10-24

grams.Proton = 1.0073 amu

Neutron = 1.0087 amuElectron = 5.486 x 10-4 amu

The typical range for atomic diameters is between 1 x 10-10

and 5 x 10-10 meters (1 and 5 )


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Periodic table Elements are divided into the general groups of:

Metals (everything on the left and middle region) Non-metals (upper diagonal on the right hand side -

green, salmon and red) Metaloids (atoms in the boundary between the metalsand non-metals): Boron(B), Silicon(Si),Germainium Ge , Arsenic As , Antimon Sb ,

Tellurium(Te), Astatine(At)). These are some of themore useful materials for semi-conductors.

The majority of elements are metals:

high luster high electrical conductivity high heat conductivity solid at room temperature (except Mercury [Hg])


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Isotopes, Atomic Numbers and

Mass Numbers All atoms of an element have the same number of

protons in the nucleus Since the net charge on an atom is 0, the atom musthave an equal number of electrons.

called isotopes.


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Molecules and IonsMolecules and chemical formulas

A molecule is comprised of two or morechemically bonded atoms. Example:

Consists of the same atoms: O2 & O3 Consists of different atoms: H2O & H2O2

Most molecular compounds (i.e. involvingchemical bonds) contain only non-metallicelements.


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Molecular, Empirical, and Structural

Formulas Molecular formulas refer to the actual number of the different

atoms which comprise a single molecule of a compound.

Empirical formulas refer to the smallest whole number ratiosof atoms in a particular compound.

Compound Molecular Formula Empirical FormulaWater H2O H2O

Hydrogen

Peroxide H2O2 HOEthylene C2H4 CH2Ethane C2H6 CH3


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Structural formulas


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Ions

The nucleus of an atom (containing protons andneutrons) remains unchanged after ordinary chemicalreactions, but atoms can readily gain or lose electrons.

In general, metal atoms tend to lose electrons, andnonmetal atoms tend to gain electrons.


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Predicting ionic charges

Many atoms gain or lose electrons such that

they end up with the same number of electronsas the noble gas closest to them in the periodictable.

,end up with the same arrangement of electronsas the noble gases, in order to achieve the samekind of electron stability.


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Ionic Compounds

The oppositelycharged ions attractone another and

bind together toform NaCl (sodiumchloride) an ionic

compound.An ionic compoundcontains positivelyand negativelycharged ions


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Ionic Compounds

The Na+ and Cl- ions arenot chemically bonded

together Cannot be described

using a molecularu .

formula instead. The concentration of ions

in an ionic compound are

such that the overallcharge is neutral.


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Naming Inorganic Compounds Two early classifications of chemical compounds:

Organic compounds. These contain the elementCarbon (C). "Life on earth is carbon based" Inorganic compounds. All other compounds


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Ionic compounds: (an association of a

cation and an anion)

The positive ion (cation) is always named first andlisted first in writing the formula for the compound.

Na+ Sodium ion Zn2+ Zinc ion + um num on

If an element can form more than one positive ion: Fe2+ iron(II) ion Fe3+ iron(III) ion Cu+ copper(I) ion Cu2+ copper(II) ion

Fe2+ ferrous ion

Fe3+

ferric ion Cu+ cuprous ion

Cu2+ cupric ion


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Ionic compounds: Anions

Monatomic anions are usually formed from non-metallicelements. Cl- chloride ion F- flouride ion 2-

O2- oxide ion Some common polyatomic anions include:

OH- hydroxide ion

CN-

cyanide ion


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Ionic compounds: Anions

Many polyatomic anions contain oxygen, and arereferred to as oxyanions. NO2

- nitrite ion

NO3- nitrate ion SO3

2- sulfite ion 2-

Some compounds can have multiple oxyanion forms (theoxyanions involving the halogens, for example): ClO- hypochloriteion ClO2

- chloriteion ClO3

- chlorateion ClO4

- perchlorateion


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Acids

An acid is a substance whose molecules yield hydrogen(H+) ions when dissolved in water.

The formula of an acid consists of an anionic groupwhose charged is balanced by one or more H+ ions.

Anions whose names end in -idehave associated acidsthat have the hydro-prefix and an -icsuffix: Cl- chloride anion HCl hydrochloricacid

S2- sulfide anion H2S hydrosulfuricacid


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Acids (oxyanions)


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Molecular compounds

The element with themore positive nature in acompound is named first.The second element isnamed with an -ide

Prefix Meaning

Mono- 1

Di- 2Tri- 3

Tetra- 4

ending. CO carbon monoxide

(carbon mono oxide)

CO2 carbon dioxide

en a-

Hexa- 6

Hepta- 7

Octa- 8

Nona- 9Deca- 10

Undeca- 11

Dodeca- 12

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02 Atomic Structure 2012