KIMIA KUANTUMKIMIA KUANTUMKIMIA KUANTUMD10B.06B3112

DRA.YATI B. YULIYATI, M.S.

Prasyarat : Kalkulus II

Kimia Fisik II

Bahasan

• Teori atom dan lahirnya kuantum• Dasar-dasar Teori Kuantum• Konsep operator• Sistem mekanika gelombang dengan energi potensial

konstan• Sistem mekanika gelombang dengan energi tidak

konstan• Interaksi materi dan energi• Struktur molekul

Pustaka

• Chandra, Introductory Quantum Chemistry• Atkins, Physical Chemistry• Engel Thomas dan Reid Philip, Physical Chemistry

Hubungan dengan kuliah ini

• Kuliah ini mendasari:– Kuliah lanjut kimia (kimia inti dan radiokimia)

• Sangat penting untuk memahami:– Struktur molekul– Spektroskopi molekul

Mekanika klasik• Perilaku atom/molekul dikaitkan dengan objek sehari-hari dan planet-

planet• Gagal menjelaskan partikel-partikel sangat kecil

Persamaan fisika klasik • Lintasan dalam hubungannya dengan energi

E = Ek + V

Energi TotalEk = Energi kinetikV = Energi potensial

21

2

mV) - E(2

dtdx

Vmv21 E

Persamaan ini untuk energi total menunjukan posisi partikel sebagai fungsi waktu (lintasan partikel)

Hukum Kedua Newton = tentang gerakan partikel

dtdx . m p

F dtdp

Gerakan RotasiMomentum sudut J sebuah partikel J = I

Osilator HarmonisGerakan osilator = vibrasi atom pada sebuah ikatan F = -kx

Gerakan Partikel Lainnya

Kegagalan Fisika Klasik

• Menerangkan transfer energi pada kuantitas yang sangat kecil• Pemerian mengenai gerakan partikel karena massa yang kecil

dan momen inersia yang kecil

Apa yang salah dengan M. Klasik ?I. Gagal menjelaskan radiasi benda hitam

• Semua benda panas mengeluarkan radiasi

• Semakin tinggi suhu, puncak bergeser ke rendah

• Secara empiris ada:

• Hk. Stefan boltzman M=k.T4, M=energi radiasi/satuan luas permukaan

• Hk. Pergeseran Wien T. max = konstan

Radiasi benda hitam• Representasi masalah radiasi ini adalah benda hitam (benda

ideal yang dapat mengabsorpsi dan memancarkan radiasi di semua rentang spektrum dengan uniform)

Penjelasan Klasik• Rayliegh dan Jeans yang melakukan

• Berdasarkan prinsip ekuipartisi, energi terserap sebagai kontinum

• Menghasilkan formula:

• Skandal UV

pd = 8kT-4d

Hipotesa Planck (Kuantum)• Berdasarkan asumsi, energi terserap tidak sebagai kontinum, tapi paket.

• Menghasilkan ungkapan:

pd = 8kT-5(ehc/kT-1)-1

II. Gagal menjelaskan Efek FotolistrikHasil Percobaan

• Tak ada elektron keluar, walau sebesar apapun intensitas, bila frekuensi ambang tak dilewati

• EK elektron yang dilepas naik dengan naiknya frekuensi, tetapi tak bergantung pada intensitas

• Pada intensitas serendah apapun, elektron tetap dilepaskan sepanjang frekuensi ambang dilewati.

Mekanika Klasik gagal• Mekanika klasik meramalkan dengan naiknya intensitas energi

elektron yang dilepas akan naik pula

• Secara klasik tak ada alasan mengapa EK harus bergantung pada frekuensi

• Sukar menjelaskan bagaimana energi dapat terkonsentrasi dalam ruang yang kecil.

Penjelasan Kuantum (Einstein)• Melangkah lebih lanjut dari Planck: tidak hanya dalam proses

penyerapan, dalam proses transportnya energi juga terkuantisasi

• Paket energi besarnya berbanding dengan frekuensi

Apa Yang Salah dengan M.Klasik ?III. Gagal menjelaskan Spektrum Atom

• Sejak abad 1 telah diamati, bila gas diberi nyala akan diamati beragam warna

• Segera dikenali dengan prisma, spektrumnya bukan kontinu

• Beberapa unsur ditemukan dengan mengenali spektrumnya

Spektrum Atom H

• 1885 Balmer menemukan ada hubungan matematik antar garis di spektrum H:

• Balmer memprediksi ada deret lain, dengan mengganti 2 dengan 1, 3, 4

= b{n2/(n2-22)}

Spektrum Atom H• Ternyata memang diamati daerah lain

• Total ada daerah:

• Lyman(uv)

• Balmer (tampak)

• Ritz (IR)

• Brackett (IR)

Mekanika Klasik Gagal• Menurut Klasik, energi kontinum, sehingga spektrum garis dengan frekuensi

tertentu tidak dapat dijelaskan

Penjelasan Kuantum (Bohr)• Energi elektron tertentu, tercermin dengan momentum sudut yang tertentu.

• Didapat ungkapan:

• En = -13.6/n2

STRUKTUR ATOM

1

Rangkaian Elektronik Instrumen Kimia

TEORI ATOMTeori Atom Thomson

Atom seperti roti kismis, yang permukaannya dipenuhi dengan muatan + dan -

Sinar Sinar ++ ++-- ++++++

++--

--------

++--HeHe

Pembuktian teori dengan menembakan sinar

--

2

Teori Atom RutherfordTeori ini mengemukakan massa atom terpusat di inti yang bermuatan positif. Elektron terletak di luar inti pada jarak yang relatif jauh dengan gerakan yang cepat

Sinar Sinar

Gaya tarik elektron dan inti diimbangi oleh gaya tarik sentrifugal

ee ee

ee ee

3

Spektrum Unsur

4

Menurut hukum fisika klasik, partikel bermuatan yang bergerak selalu kehilangan energi dengan demikian gerakan elektron makin mendekati inti dan terjadi gerakan spiral dengan kecepatan menurun. Pada suatu saat elektron bergabung dengan inti dan atom akan musnah. Dalam kenyataannya atom tidak musnah

5

Teori Atom BohrKesukaran pada teori atom Rutherford diatasi oleh Bohr. Gerakan elektron mengelilingi inti harus dengan momentum sudut tertentu.

1. Elektron dalam lintasannya mempunyai energi tertentu dan tetap selama dalam lintasan

2. Elektron dapat pindah dari lintasan yang energinya lebih tinggi ke lintasan yang energinya lebih rendah (atau sebaliknya).Bila hal ini terjadi, energi yang terbebas diubah menjadi sinar dengan frekuensi.

hEEv 12 -

6

EE11

EE22

EE33

π2

π2

hnmvnhmv

m = momentum sudut

Energinya dinyatakan chvh . . E

E1 = E2 - E1 = h. 1

E2 = E3 - E1 = h. 2

Sinar-sinar dengan frekuensi 1 dan 2 menyebabkan terjadinya spektra garis

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Partikel sub AtomPartikel sub Atom

ElektronElektron

(a) (a) A gas discharge tube. A gas discharge tube. (b) (b) Deflection of a Deflection of a cathode ray toward a positively charged platecathode ray toward a positively charged plate

8

-

+

A A cathode ray tube with an electric field cathode ray tube with an electric field perpendicular to the direction of the cathode perpendicular to the direction of the cathode rays and an external magnetic field. The rays and an external magnetic field. The symbols N and S denote the north and south symbols N and S denote the north and south poles of magnet. The cathode rays will strike poles of magnet. The cathode rays will strike the end of the tube at A in the presence of a the end of the tube at A in the presence of a magnetic field, at C in the presence of an magnetic field, at C in the presence of an electric field, and at B when there are no electric field, and at B when there are no external fields present or when the effects of external fields present or when the effects of the electric field and magnetic field cancel the electric field and magnetic field cancel each othereach other

9

A

B C

Percobaan Millikan: Penentuan Massa ElektronPercobaan Millikan: Penentuan Massa Elektron

FIGURE FIGURE 33..33 Millikan’s Millikan’s famous oil famous oil drop drop experimentexperiment

C/g 10 x 1,76 - 8me

e =e = - 1,60 x 10 - 1,60 x 101919 C C g 10 x 9,09

C/g 10 x 1,76 -C 10 x 1,60

28-

8

-19

m

10

Positively charged particles are made when cathode rays Positively charged particles are made when cathode rays (electrons) strike atoms of residual gas. They are attracted to (electrons) strike atoms of residual gas. They are attracted to the cathode, and some sail through the hole to strike the the cathode, and some sail through the hole to strike the phosphor and generate a flash of lightphosphor and generate a flash of light

ProtonProton

11

--

- -

+++

FIGURE FIGURE 33..55 Three types of rays Three types of rays emitted by radioactive elements, emitted by radioactive elements, rays rays consist of negatively consist of negatively charged particles charged particles (e(ellectrons) and are thereectrons) and are thereffore affracted ore affracted by the pasitively charged platby the pasitively charged platee. Th. Thee opposite holds true For opposite holds true For rays- rays-tthey are hey are positively charged and are drown to the positively charged and are drown to the negatively charged plnegatively charged plaattee. Because . Because rays have no chrays have no chaarge, their path is rge, their path is ununaaffecffectted by an ed by an exexternternaal electric fil electric fieeld. ld.

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Thomson’s model of the atom, sometimes described Thomson’s model of the atom, sometimes described as as the "plum pudding" the "plum pudding" model, model, after after a a traditional English traditional English dessert containing raisins. The electrons are embedded dessert containing raisins. The electrons are embedded in a in a uniform, positively charged sphere. uniform, positively charged sphere.

Positive charge spread Positive charge spread Over the entire sphereOver the entire sphere

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(a) Rutherford's experimental design for measuring the (a) Rutherford's experimental design for measuring the scattering of scattering of particles by a piece of particles by a piece of gold foil. Most of gold foil. Most of the the particles passed through the gold foil wilh little or no particles passed through the gold foil wilh little or no deflection. A few were deflected atdeflection. A few were deflected at wide angles. wide angles. Occasionally an Occasionally an particle was turn back. (b) Ma particle was turn back. (b) Maggnified nified view of view of particles pass particles passing through and being deflected ing through and being deflected by nuclei.by nuclei.

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ProtonProtonNeutronNeutron

The protons and neutrons of an atom are packed in The protons and neutrons of an atom are packed in an extremely small nucleus Electrons are shown as an extremely small nucleus Electrons are shown as "clouds" around the nucleus. "clouds" around the nucleus.

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Radiasi elektromagnetik dan spektrum atom. tingkatan energi dalam atom.

Atoms not drawn to scale, as they are joined in water, H2O Nuclei stay far apart and only the outer parts of the atoms touch

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Energi ElektromagnetEnergi Elektromagnet

The electrical force assocThe electrical force assocIaIated wted wiitthh electromagnetic electromagnetic radiation fluctuateradiation fluctuatess rhythmically. rhythmically. (a) (a) Two Two cycles of cycles of fflucluctutuaation are tion are shshown; therefore. the frequency is 2 Hz. own; therefore. the frequency is 2 Hz. (b) (b) An electromagneticAn electromagnetic ra radiation frozen in time. This curve diation frozen in time. This curve shows how the electricshows how the electricalal force varies alo force varies alonng thg thee d diirerecction of tion of travel. travel. The distThe distance ance between two maximum values ibetween two maximum values iss the the wavelewavelenngth of the egth of the ellectectrromaomaggnetic radnetic radiiatiatioon. n. 17

The SI symbol for the The SI symbol for the secondsecond is is ss. .

ss11 = = 11//ss

For any wave, the product of its wavelength For any wave, the product of its wavelength and its frequand its frequeency ncy eequaqualls ths thee velocity of the velocity of the wave. wave.

== Hertz Hertz == (Hz)(Hz) 1 Hz 1 Hz = = 11ss-1-1 Lamda Lamda = = = Panjang Gelombang = Panjang Gelombang

KecKec.. Cahaya Cahaya = = c c = 3,00 x 10= 3,00 x 1088 mmss-1-1

. . = = c c = 3= 3,,00 x 1000 x 1088 m mss-1-1 18

The electromagnetic spectrum

Spektrum Elektromagnetik

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Infrared spectrum of methyl alcohol, alkohol kayu

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(a) A diagram showing how white light is refracted by a glass prism, which spreads out the colour of the visible spectrum

(b) In this color photograph we see the continuous rainbow of colors formed from white light.

Energi Gelombang Cahaya Energi 1 Foton = E = hEnergi 1 Foton = Quantum h = Konstanta Plank = frekuensi

(a)(a)

(b)(b)21

Production of a line spectrum. The light emitted by excited atoms is formed into a narrow beam and passed through a prism. This light beam is divide into relatively few narrow beams with frequencies that are characteristic of the particular eIement that is emitting the light.

Spektrum Atom

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Spektrum kontinyu E = h

Ball on a staircase. The ball can have only certain amounts of potential energy when at rest.

Apabila atom Hidrogen mengemisi sinar pada frekuensi 4,57 x 1014 Hz,atau = 656 nm energi atom akan menurun sejumlah 3,03 x 10-19 J.

Apabila atom tereksitasi, energi yang dilepaskan besarnya tertentu.

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n = Bilangan Kuantum k = 218x10-18 J E = Energi Elektron Ground State = Keadaan Energi Terendah

Model Atom Bohr .. Absorption of energy and emission of light by the hydrogen atom, When the atom absorbs energy, the electron is raised to a higher energy level. When the electron falls to a lower energy level, light of a particular energy and frequency is emitted

2nk- E

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Gelombang Elektron dalam Atom

2-n

LOrbital = bentuk gelombang elektron

Bilangan Kuantum Utama = n

n = 1 - ~

n 1 2 3 4 ...

Kulit K L M N ...

Bilangan kuantum kedua = l = sub kulit bilangan kuantum azimuth. Untuk setiap harga n; l = O sampai dengan l = n -1

l 1 2 3 4 5 6 … Sub Kulit s p d f g h … 25

1 0 2 0,1 3 0, 1, 2 4 0, 1, 2, 3 5 0, 1, 2, 3, 4

TABLE Relationship between n and l

Value of nValue of n Value of Value of l

4s < 4p < 4d < 4f

Energi bertambah besar

Bilangan Kuantum Magnet = ml

Untuk setiap harga l, harga ml adalah -I s/d +l 26

27

FIGURE 3.17 Approximate energy level diagram for atoms with two or more electrons. The quantum numbers associated with the orbitals in the first two shells are also shown.

28

Spin Elektron = ms

ms = + ½ atau – ½ Prinsip Pauli

29

A paramagnetic A paramagnetic substance is attracted substance is attracted to a magnetic fieldto a magnetic field

30

Konfigurasi Elektron = Struktur Elektronik

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Aturan Hund : A way to remember the fiIling order of subshells. Write the subshell designations as shown and follow the diagonal arrows, starting at the bottom.

Core Electrons: Na [Ne] 3s1

Mg [Ne] 3s2 32

Konfigurasi Elektron dalam Tabel Perioda

FIGURE 3.20FIGURE 3.20 Overall structure of Overall structure of the periodic tablethe periodic table

FIGURE 3.19FIGURE 3.19 Subshell Subshell that become field as that become field as we cross periodeswe cross periodes

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Kedudukan Elektron Setiap Saat

FIGURE 3.22 Size variation among s orbitals become larger with increasing n. The diagrams represent cross sections of the spherical electron density patterns.

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The shapes and directional properties of the five d orbitals of a d subshell

probabiIity distribution in a p orbital.

The orientations of the three p orbitals in a p subshell.

35

Large atom are found in the lower left of the periodic table, and small atoms are found in the upper right

Ukuran Atom dan Ion

Jari -jari Atom 7,0 x 10-11 m s/d 2,9 x 10-11 m

36

Variations in atomic and ionic radii in the periodic Variations in atomic and ionic radii in the periodic table. Value are in picometerstable. Value are in picometers

37

Ukuran Ion

38

Energi lonisasi = EA Adalah energi yang diperlukan untuk melepaskan satu elektron dari sebuah atom bebas.

X(g) X-(g) + e

TABLE 3.3 Successive Ionization Energies in kJ/mol for Hydrogen through Magnesium

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FIGURE 3.27FIGURE 3.27 The variation of first ionization The variation of first ionization energy with atomic numberenergy with atomic number

40

FIGURE 3.28FIGURE 3.28 Variations of ionization energy Variations of ionization energy within the periodic table. within the periodic table.

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Afinitas Elektron = EAAdalah energi yang dilepaskan apabila satu elektron ditambahkan kepada atom bebas

X(g) + e- X-(g)

TABLE 3.4 Electron Affinities for Some Elements

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