Slide 2 Matter and Properties of Matter

8/8/2019 Slide 2 Matter and Properties of Matter

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Matter and Properties ofMatter and Properties of

MattersMatters

KEY IDEA: Properties of materials depend on theiratoms, and how those atoms are linked together

1. Matter

Properties of matter

States of matter

2. Chemical Bonding

Bonding theory

Molecular Structure(VSEPR)

3. Intermolecular Forces

States of MatterStates of Matter

SOLIDSSOLIDS

(fixed volume and shape)(fixed volume and shape)

Crystal regularatomic arrangement

SOLIDSSOLIDS

(fixed volume and shape)(fixed volume and shape)

Glass: Atoms not periodic

Glass vs. Crystal StructureGlass vs. Crystal Structure LIQUIDSLIQUIDS(fixed volume, variable shape)(fixed volume, variable shape)


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LIQUIDSLIQUIDS

(fixed volume, variable shape)(fixed volume, variable shape)Liquid Crystals: Molecules line up under an electric field

GASGAS

(variable volume and shape)(variable volume and shape)

PLASMAPLASMA

(Gas with free electrons)(Gas with free electrons)Properties of Matter

Physical properties properties that we can measure and describe, including shape,

color, and texture

Chemical properties chemical properties, such as their flammability

Macroscopic Physical and chemical properties that can be observed with the

eye

Microscopic

The underlying structure of a chemical substance, that can beexplored using magnifying devices

Iron at atomic, miscroscopicand macroscopic levels

atomthe smallest possible particleof a substance

moleculea combination of two or moreatoms held together in aspecific shape by attractiveforces.

A chemical compound is a substancethat contains more than one element.

chemical elementA substance that contains only one type of atom (eachdifferent element contains its own specific type of atom),cannot be decomposed into other chemical components


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Classifications

good conductors of heat and electricity and usuallyappear shiny.malleable, meaning that they can be hammered intothin sheetsductile meaning that they can be drawn into wiresExcept for mercury, which is a liquid, all metals aresolids at room temperature.

poor conductors of electricity and heat

six elements that are categorized asmetalloidsdull-appearing, brittle solids aresometimes called semiconductors

because they conduct electricitybetter than nonmetals but not as wellas metals.Silicon and germanium are used inthe manufacture of semiconductorchips in the electronics industry.

A mixture contains two or more chemical substances.Unlike pure compounds, mixtures vary in composition because theproportions of the substances in a mixture can change.For example, dissolving sucrose and table sugar in water forms amixture that contains water molecules and sucrose molecules.

A sample is homogeneous if it always has the same composition, no matter what

part of the sample is examined.

Pure elements and pure chemical compounds are homogeneous.Mixtures can be homogeneous, too; a homogeneous mixture usually is called asolution.

Hydrogen chloride gas is a homogeneous pure substance and always containsequal numbers of hydrogen atoms and chlorine atoms linked in HCl molecules.

Under other conditions, molecular hydrogen and molecular chlorine do not reactwith each other. The two gases form a homogeneous solutionwhosecomposition can be changed by adding more of either substance.

Phase of matter

solidliquid

gas

tentukan karakteristik substansi pada dua gambar diatasmeliputi fasa dan jenisnya

transformation of matter: phase

Dimension

interstellar(sun-star)

distance

1016 m

1011 m

107 m

10-3 m

102 m

104 m

10-7 m

10-10 m

10-15 m

sun-earthdistance

diameter

of earth

SF-Berkeley

distance

football field

blade of

grass

chlorophyll

molecule

H atom

H nuclei


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Measurements in chemistryLength, area, and volume measure thesize of an object. Length refers to onedimension, area refers to two dimensions,and volume refers to three dimensions ofspace.

every object possesses a certainquantity of matter, called its mass highly accurate mass-measuringmachines, called analyticalbalances, work by comparingforces acting on masses.

The process of determining mass is calledweighing.Mass and weight are related, but they are not the same property.Mass is a fundamental characteristic of an object, whereas weight resultsfrom gravitational force acting on an object's mass.

precision describes the exactness of a measurementaccuracy describes how close a measurement is to the true value.

presisi dan akurasi

cermat dan akurat

cermat dantidakakurat

tidak cermatdan tidak akurat

significant figures

A property that depends on amount is called extensive.Mass and volume are two examples of extensive properties.

A property that is independent of amount is called intensive.Density and temperature are intensive properties.

extensive and intensive properties

Chemical BondingChemical Bonding

Atoms link together by the rearrangementof their electrons

Magic numbers (2,10,18,&36) of electronsform very stable atoms

Electrons may be transferred or shared toform stable bonds

Ionic Bonds

Covalent Bonds

Metallic Bonds

IKATAN KIMIA

Mengapa beberapa senyawa padatan meleleh pada

suhu tinggi, sedangkan cairan atau gas pada suhu

kamar?

Mengapa atom-atom unsur yang berbeda

bereaksi?

Bagaimana bentuk geometri suatu senyawa?

menyatakan gaya tarik antar atom bersama membentuk suatusenyawa

menentukan sifat kimia suatu senyawa dan mengontrol jumlah energi yang dilepas/diserap dalam suatu reaksi Menentukan bentuk/geometri suatu senyawa

0

Ep

Jarak antar inti

74 pm

436 kJ/mol

= atom H

Energi interaksi antara 2 atom H

Gaya tolak Gaya tarik

molekul H2 terbentuk dengan Ep=-436 kJ/mol pada jarak antarinti 74 pm

jarak antar inti yang memberikan energi potensial molekulpaling rendah dapat ditentukan secara eksperimen ikatankimia

PEMBENTUKAN MOLEKUL GAS HIDROGEN, H2


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Teori Lewis

1. Yang berperan dalam ikatan kimia adalah elektron,terutama elektron kulit terluar (elektron valensi)

2. Elektron valensi umumnya dipindahkan dari atom logamke non-logam dan terbentuk kation dan anion. Gaya

elektrostatik antar kation-anion menghasilkan IKATANIONIK.

3. Pada ikatan antar atom non-logam, 1 atau lebihpasangan elektron valensi digunakan bersama oleh atomyang berikatan membentuk IKATAN KOVALEN.

4. Dalam melepaskan atau menarik atau menggunakanelektron bersama untuk membentuk ikatan kimia, atom-atom cenderung mencapai konfigurasi gas mulia (Aturanoktet/Aturan gas mulia) untuk mencapai stabilitasmaksimum.

STRUKTUR LEWIS

Menggunakan nama kimia atom untuk menyatakan inti danelektron di kulit selain kulit valensi (core electrons) dan titikuntuk menyatakan elektron valensi

Struktur Lewis tidak secara khusus menyatakan cara elektron

berpasangan

Contoh: Si P

Grup 4A Grup 5A

Tentukan struktur Lewis ion berikut:a. Al3+ b. N3- c. S2-

IKATAN IONIK

Pembentukan ikatan ionik lebih banyak dikontrol oleh energipotensial pembentukan ion (energi ionisasi dan affinitaselektron)

Ikatan ionik yang stabil mempunyai energi total pembentukanion-ion penyusun ikatan bersifat EKSOTERMIS: energipotensial senyawa < energi potensial individu unsur

Pada atom non-logam:E untuk melepas e- > Energi untuk menangkap e- ANION

Pada atom logam:E untuk melepas e- < Energi untuk menangkap e- KATION

Contoh: pembentukan NaCl

Na + e-Na+

Cl + e-

Cl-

2Na(padatan) + Cl2(gas) 2NaCl(padatan)

Ikatan ionik Gaya elektrostatik yang mengikat ion positif

(kation) dan ion negatif (anion) dalam suatusenyawa senyawa ionik

Eg: reaksi antara litium dan flourinmembentuk litium fluorida (serbuk putihberacun yang dipakai untuk menurunkantitik leleh solder dan pembuatan keramik)

PERUBAHAN ENERGI DALAM PEMBENTUKAN

SENYAWA IONIK

PERUBAHAN ENERGI DALAM PEMBENTUKAN

SENYAWA IONIKNa(g) + e-Na+(g)

+ e-

Na(padatan) + 1/2Cl2(gas) NaCl(padatan) Hof=-411 kJ

EI1=+496 kJ/mol

Cl(g) Cl-(g) AE=-349 kJ/mol

Total energi perpindahan 1e- dari atom Na ke atom Cl =(+496) + (-349) = +147 kJ/mol

reaksi sukar terjadi

Reaksi berlangsung

Perubahan energi pada pembentukan NaCl dapat ditentukanmenggunakan

Siklus Born-Haber

Starting point: 1 mol Na(s) dan mol Cl2(g)End point: 1 mol NaCl(s)

Siklus Born-Haber untuk 1 mol NaCl

end

Na+(g) + Cl(g) + e-

H1 = +107 kJ

H3 = +496 kJ

H2 = +122 kJ

H4 = -349 kJ

H5 = -787 kJ

Hfo NaCl(s) = -411 kJ

Na+(g) + Cl-(g)

start

Na(g) + Cl(g)

Na(s) + 1/2Cl2(g)

Na(g) + 1/2Cl2(g)

NaCl(s)

1

2

34

5


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Reaksi yang terlibat dalam pembentukan NaCl

1. Konversi atom Na dari fasa padat ke fasa gas H12. Disosiasi/peruraian molekul Cl2 menjadi atom-atom Cl

H2 (energi disosiasi ikatan)

3. Ionisasi atom Na fasa gas menjadi ion Na+ fasa gas H3(Energi ionisasi pertama, EI1)

4. Konversi atom Cl fasa gas menjadi ion Cl- fasa gas H4(Afinitas elektron)

5. Pembentukan sistem kristal dari ion-ion fasa gas H5(energi kisi)

Hfo = H1 + H2 + H3 + H4 + H5 = -411kJ

Entalpi sublimasi Li +161 kJ/mol dan EI1=+520 kJ/mol.Energi disosiasi Fluorin +159 kJ/mol F2 dan EA fluorin -328kJ/mol. Energi kisi LiF -1047 kJ/mol. Tentukan perubahanenergi entalpi total reaksi:Li(s) + 1/2F2(g) LiF(s) Hof=?

ENERGI KISI

Energi yang dibutuhkan untuk memisahkan secara sempurna 1mol senyawa ionik padatan menjadi ion-ion fasa gasnya.

ditentukan dari Hk Coulomb: E = k (Q+Q-)/r

ditentukan secara tidak langsung menggunakan konsep siklusBorn-Haber

IKATAN KOVALEN

Cl Cl Cl Cl

Lone pair

Bonding pair

IKATAN KOVALEN KOORDINASI

1 atom menyediakan 2 elektron untuk dipakai bersama

membentuk ikatan

Pembentukan H3O+

TEKNIK PENULISAN STRUKTUR LEWIS

1. Tentukan total jumlah elektron valensi atom-atom yangberikatan

2. Buat struktur rangka (hubungkan atom yang berikatandengan garis)

3. Tempatkan lone pair elektron di atom terminal (ujung)untuk mencapai konfigurasi oktet pada atom palingujung (kecuali H)

4. Susun elektron tersisa sebagai lone pair di sekitar atompusat

5. Jika perlu, pindahkan 1 atau lebih elektron lone pair dariatom terminal untuk membentuk ikatan rangkap denganatom pusat

IKATAN KOVALEN DAN ELEKTRONEGATIVITAS

Elektronegativitasmenyatakan kemampuan suatu atom

untukmenarik elektron ikatan saat atom berada sebagai

suatu molekul

makin besar elektronegativitas atom dalam suatumolekul, makin kuat atom tersebut menarik elektronikatan kovalen

Dalam satu periode SPU, secara umum elektronegativitasmeningkat dari kiri ke kanan

Dalam satu golongan SPU, secara umumelektronegativitas meningkat dari bawah ke atas


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non

polar

covalentbond

increasing ionic character

polar covalent bond ionic bond

increasing covalent character

0 0.5 1.0 1.5 2.0 2.5 3.0

-102-51-112-69193714801melting point

Cl2SCl6PCl3SiCl4AlCl3MgCl2NaClcompound

Chlorides of Period 3

-102-121-40-23-107415610melting point

Cl2OCl2NCl3CCl4BCl3BeCl2LiClcompound


melting point senyawa periode 2 dan 3

What is the trend?

lowhigh

Conductivity -h igh Conductivity - l ow

What about the distancebetween the atoms in a bond?

NaCl Na+ Cl- d = 281 pm

Cl2 Cl-Cl d = 199 pm

What property can be used to tellwhen a bond will ionic or covalent?

Electronegativity

00.61.01.31.61.92.2EN

Cl2SCl6PCl3SiCl4AlCl3MgCl2NaClCompound


00.600.61.11.62.2EN



large difference small difference

The electronegativity difference - EN = ENhigher EN lower

Using electronegativitiesto determine bond type

EN > 1.7 ionic bond - transfer

EN < 1.7 covalent bond - sharing

So we have a range of electronegativity difference of0 to 1.7 for sharing an electron pair.


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Is the sharing of electronsin molecules always equal?

X Y EN = 0

X Y EN = 0.3

X Y EN = 0.6

X Y EN = 0.9

X Y EN = 1.2

ENY > ENX

Which elementis moreelectronegative?

non-polarbond

increasing

polarity

of

bond

polar bond

0 < EN< 1.7

Direction of electron migration

Molecular compounds are typically gases, liquids, or lowmelting point solids and are characteristically poorconductors. Examples are H2O, CH4, NH3.

Nonmetallic element + nonmetallic element Molecular compound

Metallic compound + nonmetallic compound IONICcompound

Ionic compounds are generally high-melting solids thatare good conductors of heat and electricity in themolten state.Examples are NaCl, common salt, and NaF, sodiumfluoride.

BF3 a planar molecule

Ball & stick

BF

Space-filled

Electrostatic potential maps

topside

negative

positive

Spartan 02

2.0

4.0

Bond Energy

F2 single bond BE = 142 kJ/mole

O2 double bond BE = 494

N2 triple bond BE = 942

X2 + energy X + X

increasing

bond

strength

Is breaking a bond an endothermic or exothermic process?

http://wulfenite.fandm.edu/Data%20/Table_6.html

Show the direction of electronmigration ( ) in the following.

C H

H F

C = O

C Cl

Rank the bond polarity (1-most 3-least)

As-H N-H P-H


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ionic covalent

valenceelectrons

Comparison of Bonding Types

sharing ofelectrons

transfer ofelectrons

ions molecules

EN > 1.7 EN < 1.7

high mp low mp

molten saltsconductive

non-conductive

Bonding spectrum

100% covalent 100% ionic

A+ B-A B A B

Increasing EN

Increasing polarity Transfer

Here is the electrostatic potential map for H2CO.

Show the electronmigration on thisplanar molecule.

C OH

H

How is this molecule different than BF3?

blue positive red - negative -102-51-112-69193714801melting point

Cl2SCl6PCl3SiCl4AlCl3MgCl2NaClcompound


-102-121-40-23-107415610melting point



melting point senyawa periode 2 dan 3

What is the trend?

lowhigh

Conductivity -h igh Conductivity - l ow

What about the distancebetween the atoms in a bond?

NaCl Na+ Cl- d = 281 pm

Cl2 Cl-Cl d = 199 pm

What property can be used to tellwhen a bond will ionic or covalent?

Electronegativity

00.61.01.31.61.92.2EN

Cl2SCl6PCl3SiCl4AlCl3MgCl2NaClCompound


00.600.61.11.62.2EN



large difference small difference

The electronegativity difference - EN = ENhigher EN lower


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Using electronegativitiesto determine bond type

EN > 1.7 ionic bond - transfer

EN < 1.7 covalent bond - sharing

So we have a range of electronegativity difference of0 to 1.7 for sharing an electron pair.

Is the sharing of electronsin molecules always equal?

X Y EN = 0

X Y EN = 0.3

X Y EN = 0.6

X Y EN = 0.9

X Y EN = 1.2

ENY > ENX

Which elementis moreelectronegative?

non-polarbond

increasing

polarity

of

bond

polar bond

0 < EN< 1.7

Direction of electron migration

Molecular compounds are typically gases, liquids, or lowmelting point solids and are characteristically poorconductors. Examples are H2O, CH4, NH3.

Nonmetallic element + nonmetallic element Molecular compound

Metallic compound + nonmetallic compound IONICcompound

Ionic compounds are generally high-melting solids thatare good conductors of heat and electricity in themolten state.Examples are NaCl, common salt, and NaF, sodiumfluoride.

BF3 a planar molecule

Ball & stick

BF

Space-filled

Electrostatic potential maps

top side

negative

positive

Spartan 02

2.0

4.0

Bond Energy

F2 single bond BE = 142 kJ/mole

O2 double bond BE = 494

N2 triple bond BE = 942

X2 + energy X + X

increasing

bond

strength

Is breaking a bond an endothermic or exothermic process?

http://wulfenite.fandm.edu/Data%20/Table_6.html


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Show the direction of electronmigration ( ) in the following.

C H

H F

C = O

C Cl

Rank the bond polarity (1-most 3-least)

As-H N-H P-H

ionic covalent

valenceelectrons

Comparison of Bonding Types

sharing ofelectrons

transfer ofelectrons

ions molecules

EN > 1.7 EN < 1.7

high mp low mp

molten saltsconductive

non-conductive

Bonding spectrum

100% covalent 100% ionic

A+ B-A B A B

Increasing EN

Increasing polarity Transfer

Here is the electrostatic potential map for H2CO.

Show the electronmigration on thisplanar molecule.

C OH

H

How is this molecule different than BF3?

blue positive red - negative

TEORI IKATAN DAN BENTUKMOLEKUL

METODE TOLAKAN PASANGAN ELEKTRON KULITVALENSI (VSEPR:valence-shell electron-pair repulsion)

Konsep: pasangan elektron pada kulit valensi atom-atom yang berikatan saling

memberikan tolakan antara yang satu dengan yang lain sedemikian rupa sehinggamenempati ruang sejauh mungkin terhadap pasangan elektron yang lain

Geometri molekul dengan energi tolakan minimum

Terms:1. Geometri gugus elektron: orientasi ruang gugus elektron di sekitar atom pusat

akibat tolakan antara gugus elektronGugus elektron: kelompok elektron valensi yang terlokalisasi di sekitar atompusat

2. Geometri molekul bentuk molekul: orientasi ruang atom-atom yang berikatandi sekitar atom pusat

Geometri gugus elektron2 gugus elektron: linier; 3 gugus elektron: segitiga planar (trigonalplanar); 4 gugus elektron: tetrahedral; 5 gugus elektron: trigonalbipiramidal; 6 gugus elektron: oktahedral

Jika tidak ada lone-pair electrons (lp), geometri gugus elektron =geometri molekul

Jika ada lone-pair electrons (lp), geometri molekul ditentukan olehgeometri gugus elektron

Cara menerapkan VSEPR:1. Gambar struktur Lewis yang stabil2. Tentukan jumlah gugus elektron sekitar atom pusat dan

identifikasikan sebagai gugus elektron ikatan (bonding pair, bp) ataulone-pair electrons (lp)

3. Tentukan geometri gugus elektronnya4. Deskripsikan geometri molekulnya5. Derajat kuat tolakan: lp-lp > lp-bp > bp- bp


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67Structure Determination by VSEPRStructure Determination by VSEPRWater, HWater, H22OO

The electron pair geometryThe electron pair geometry

isis TETRAHEDRALTETRAHEDRAL

The molecularThe molecular

geometry isgeometry is BENTBENT..

2 bond pairs2 bond pairs

2 lone pairs2 lone pairs

H O H

H O H

68

Structure Determination by VSEPRStructure Determination by VSEPRAmmonia, NHAmmonia, NH33

The electron pair geometry is tetrahedral.The electron pair geometry is tetrahedral.

H

H

H

lone pair of electronsin tetrahedral position

N

TheThe MOLECULAR GEOMETRYMOLECULAR GEOMETRY thethepositions of the atomspositions of the atoms isis TRIGONALTRIGONAL

PYRAMIDPYRAMID..

CH4

Ukuran relatif pasangan elektron ikatan danlone pairs pada molekul CH4, NH3 dan H2O

Molecular Geometry

Predict the molecular geometry of IF5.

Lewis structure:

Geometri gugus elektron:

Geometri molekul:

2

3

4


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4

5

6

MOLEKUL POLAR DAN MOMEN DIPOLMolekul yang memiliki pusat muatan positif dan negatifterpisahkan oleh suatu jarak tertentu.

Kuantifikasi terhadap pemisahan muatan dalam suatumolekul dinyatakan oleh momen dipol (, debye, D), hasilkali jarak yang memisahkan pusat muatan positif dannegatif (d, meter) dengan kuantitas muatan (, coulomb)

= d

1 D = 3,34 x 10 -30 C m

Molekul polar momen dipol 0Molekul non-polar momen dipol = 0

Plat logam Medium non-konduktifJika molekul polar ditempatkan antara kedua plat logam,molekul tsb akan mengalami penataan seperti gambar di atas

Molekul polar meningkatkan kapasitas penyimpanan muatanplat logam sampai pada suatu kuantitas yang sesuai denganmomen dipol molekul

77

Bond PolarityBond PolarityHClHCl isis POLARPOLAR because it has abecause it has a

positive end and a negativepositive end and a negativeend. (difference inend. (difference inelectronegativityelectronegativity))

ClCl has a greater share inhas a greater share in

bonding electrons thanbonding electrons than

does H.does H.

ClCl has slight negative chargehas slight negative charge ((--)) and H hasand H hasslight positive chargeslight positive charge (+(+ ))

H C l

+ -

78

Molecular Dipole Moments

For polyatomic molecules, the dipole moment is thegeometric sumof all bond dipole moments.

CO2 - Nonpolar H2O - Polar


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79

This is why oil and water will not mix! Oil isThis is why oil and water will not mix! Oil is nonpolarnonpolar, and, andwater is polar.water is polar.

The two will repel each other, and so you can not dissolveThe two will repel each other, and so you can not dissolveone in the otherone in the other

Like dissolves likeLike dissolves like

Bond PolarityBond Polarity80

Predict the Polarity ofMolecules:

HCl

CCl4NH3BF3

CH3Cl

Determine the dipol direction(electron migration)

881

Overview

Geometry and Directional Bonding

Valence-Shell Electron-Pair Repulsion Theory

Dipole Moment and Molecular Geometry

Valence Bond Theory

Description of Multiple Bonding

Molecular Orbital Theory

Principles of Molecular Orbital Theory

Electron Configurations of Diatomic Molecules of theSecond-Period Elements

Molecular Orbitals and Delocalized Bonding

882

Molecular Geometry and DirectionalBonding

Atoms oriented in very well defined relative positionsin the molecule.

Molecular Geometry = general shape of themolecule as determined by the relative positions ofthe atomic nuclei.

Theories Describing the structure and bonding ofmolecules are: VSEPR= considers mostly electrostatics in determining the

geometry of the molecule.

Valence Bond Theory= considers quantum mechanics andhybridization of atomic orbitals.

Molecular Orbital Theory= claims that upon bond formationnew orbitals that are linear combinations of the atomic

orbitals are formed.

TEORI IKATAN VALENSI

Teknik: gambar struktur lewis Perkirakan penataan semua pasang-an elektron

menggunakan metode VSEPR Tentukan hibridisasi atom pusat dengan cara

memadankan pasangan e- dengan orbital hibrida

Asumsi:Elektron suatu molekul menempati orbitalatomnya masing-masing

Molekul stabil terbentuk dari atom-atom yang

bereaksi jika energi potensialnya minimum

884

MOLECULAR SHAPES:VALENCEBOND THEORY (VBT)

Valence Bond Theory: a quantum mechanical description ofbonding that pictures covalent bond formation as the overlap oftwo singly occupied atomic orbitals.

VSEPR effective but ignores the orbital concepts discussed inquantum mechanics.

H2 forms due to overlap of two 1s orbitals. Electron densities from p-subshell electrons overlap to produce

a bond in F2. CH4:The 1s orbital of hydrogen must overlap with the 2s and 2p

orbitals of carbon. Presence of electrons from hydrogen adds new waves that are

in contact with each other and undergo constructive interference new waves result.

The s and p orbitals around an atom such as carbon becomeequivalent and the orbitals become a hybrid(sp3) of the originalorbitals.

Hybrid orbitals are as far apart as possible.


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885

Other Kinds of Hybrid Orbitals

Hybridization varies from sp, sp2, up to sp3d2depending uponthe number of orbitals involved in the bonding.

Each of these has a characteristic shape see table in book.

Hybridization determined by using VSEPR to establish the

geometry, i.e., the number of electron clouds around the centralatom. The number of electron clouds = the number of hybridorbitals.

E.g.: Determine the hybridization of B in BF3.

The bond formed between an s orbital and a p orbital or evenbetween two p orbitals.

E.g. CH3CH2OH, has all bonds - even though there are C-Cbonds and C-O bonds which each involve the interaction of sp3

orbitals to form the bonds. SF6: sp3d2. 886

VBT: Multiple bonds

C2H4 planar with a trigonal geometry = sp2

hybridization for each of the carbon atoms andthey form bonds with hydrogen.

Each carbon has 4 orbitals in its valence shell.This means one of the p-orbitals for each C is nothybridized.

Proximity to each other results in overlap to givea charge distribution resembling a cloud which isabove and below the plane of the molecule andcalled a bond .

Overlap above and below makes rotation ofcarbon atoms difficult.

E.g. C2H2: sp (linear) hybridized. Leads to theexistence of a bond as well as two bonds.

S um mari zi ng a

single bond is a bond, double bond is a bond and a bond, triple bond is a bond and 2 bonds.E.g. Dinitrogen difluorideexists as cisand trans

isomers( a compound having the same formulawith a different arrangement of atoms).Investigate the bonding.

887

Hybrid Orbitals

S in SF66Octahedralsp3d2

P in PCl55Trigonal bipyramidalsp3d

C in CH44Tetrahedralsp3

B in BF33Trigonal planarsp2

Be in BeF22Linearsp

ExampleNumber ofOrbitals

Geometric ArrangementsHybridOrbitals

Untuk atom O dalam H2O

O atom

(ground state)

Energy

1s

2p

2s

sp3

1s

sp3

1s

O atom

(hybridized state)

O atom

(in H2O)

O-H

bonds

lone

pairs

Pembentukan orbital hibrida sp3 Pembentukan orbital hibrida sp


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Pembentukan orbital hibrida sp2

Multiple Bonding

According to valence bond theory, onehybrid orbital is needed for each bond

(whether a single or multiple) and for eachlone pair.

For example, consider the molecule ethene.

Multiple Bonding

Each carbon atom is bonded to three otheratoms and no lone pairs, which indicatesthe need for three hybrid orbitals.

This implies sp2 hybridization.

The third 2p orbital is left unhybridized and lies

perpendicular to the plane of the trigonal sp2

hybrids.

The following slide represents the sp2

hybridization of the carbon atoms.

C atom (ground state)

2s

2p

Energy

sp2

2p

1s 1s

C atom (hybridized)

(unhybridized)

Multiple Bonding

To describe the multiple bonding inethene, we must first distinguish between

two kinds of bonds. A (sigma) bond is a head-to-head overlap of

orbitals with a cylindrical shape about the bond

axis. This occurs when two s orbitals overlap orp orbitals overlap along their axis.

A (pi) bond is a side-to-side overlap of parallelp orbitals, creating an electron distribution above

and below the bond axis.

Figure 10.25


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Multiple Bonding

The remaining unhybridized 2p orbitalson each of the carbon atoms overlap side-

to-side forming a bond.

You therefore describe the carbon-carbon double

bond as one bond and one bond.

Bonding in Ethylene

Pembentukan orbital hibrida pada molekulberikatan rangkap

C2H4etilen

C2H2asetilen

8101

MO Theory of Bonding

Molecular Orbital Theory extends quantum theory and statesthat electrons spread throughout the molecule in molecularorbitals = region in a molecule in which an electron is likely tobe which is similar to the concept discussed in quantum theory.Molecular orbitals are considered to be the result of the

combination of atomic orbitals.

Hydrogen: when two atomic orbitals from hydrogen approacheach other they form 2molecular orbitals, and *, bondingorbital and antibonding orbital respectively. The energy of the bonding orbital is lower than the original atomic

orbital. The energy of the antibonding orbital is higher than the original

atomic orbitals and thus destabilizes the molecule.

The electron distribution of H2 would be: 1s , . Anexcited state of this molecule would be 1s , .

*s1

*s2 8102

H atom H atomH2 molecule

1s 1s

1s

1s*

Because the energy of the two electrons is lower than the energy of theindividual atoms, the molecule is stable.


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8103

Bond Order

The term bond order refers to the number of bondsthat exist between two atoms.

The bond order of a diatomic molecule is defined asone-half the difference between the number of

electrons in bonding orbitals, nb, and the number ofelectrons in antibonding orbitals, na.

)n-(norderbond ab21=

8104

Molecular Orbital Theory of OtherDiatomic Molecules

He2: no net stabilization (orbonding).

a net of one bonding electron.

Bond order: BO = 1/2(nb na) where nb is thenumber of bonding electrons and na is the number

of antibonding electrons.E.g. For He2 BO(He2) = 1/2(2 2) = 0.E.g.2 H2 on the other hand would have a BO(H2) =

1/2(2 0) = 1 or there is a single bond betweenthe two atoms.

Li2: BO=1/2(4 2) = 1.

Molecule of lithium should be stable. O2: ;

BO= 1/2(10 6) = 2. Last two filled orbitals areantibonding one elctron in each orbital (Hundsrule) or two unpaired electrons O2 aparamagnetic molecule.

( ) ( )1121 *ss ( ) ( )2121 *ss

+2He

( ) ( ) ( )221

12

1 s*ss

( ) ( ) ( ) ( ) ( ) ( ) ( )2222422

22

22

12

1*ppp

*ss

*ss

Fig. 10.34 MO Diagram ofN2

8105

MO Levels of 2nd Row Elements

*p2

*p2

p2

p2

*s2

s2

B2 C2 N2 O2 F2 Ne2

Large 2s-2p interaction Small 2s-2p interaction

Bond Order

Magnetic behavior

1

P

2

D

3

D

2

P

1

D

0

P = Paramagnetic; D = Diamagnetic

8106

Delocalized Bonding

Molecular orbital theory handles delocalization quite nicely since molecularorbitals can be said to be spread over the entire.

Metals and energy bands formed by them.

Solidification of metal atoms forms large molecules with extensivedelocalization of electrons.

Molecular orbitalsfor all metals are very similar and a continuous band is formed.

They can conduct electricity when the atoms are excited so that an electronoccupies an excited state. The energy separation between the occupied andunoccupied orbitals is small so that little energy is required to cause this.

8107

Fig. 10.34 MO Diagram of N2

8108

INTERMOLECULAR FORCES


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A Molecular Comparison of

Gases, Liquids and Solids Physical properties of substances understood in terms of

kinetic molecular theory: Gases are highly compressible, assumes shape and volume of

container: Gas molecules are far apart and do not interact much with each

other.

Liquids are almost incompressible, assume the shape but notthe volume of container:

Liquids molecules are held closer together than gas molecules, butnot so rigidly that the molecules cannot slide past each other.

Solids are incompressible and have a definite shape andvolume:

Solid molecules are packed closely together. The molecules are sorigidly packed that they cannot easily slide past each other.

A Molecular Comparison of

Gases, Liquids and Solids

A Molecular Comparison of Gases,

Liquids and Solids

Converting a gas into a liquid or solid requires themolecules to get closer to each other: cool or compress.

Converting a solid into a liquid or gas requires themolecules to move further apart: heat or reduce pressure.

The forces holding solids and liquids together arecalled intermolecular forces.

Intermolecular Forces

The covalent bond holding a molecule together is anintramolecular force.

The attraction between molecules is an intermolecularforce.

Intermolecular forces are much weaker thanintramolecular forces (e.g. 16 kJ/mol vs. 431 kJ/mol forHCl).

When a substance melts or boils the intermolecularforces are broken (not the covalent bonds).

When a substance condenses intermolecular forces areformed.

Intermolecular Forces in Solutions


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Intermolecular Forces Intermolecular Forces

Ion-Dipole Forces Interaction between an ion (e.g. Na+) and a dipole

(e.g. water).

Strongest of all intermolecular forces:

Since Q1 is a full charge and Q2 is a partial charge, Fiscomparatively large.

Fincreases as Q increases and as ddecreases: the larger the charge and smaller the ion, the larger the

ion-dipole attraction.

221

d

QQkF =

Intermolecular Forces Intermolecular Forces

Dipole-Dipole Forces Dipole-dipole forces exist between neutral polar

molecules.

Polar molecules need to be close together.

Weaker than ion-dipole forces:

Q1 and Q2 arepartial charges.

221

d

QQkF =


Dipole-Dipole Forces There is a mix of attractive and

repulsive dipole-dipole forces asthe molecules tumble.

If two molecules have about thesame mass and size, then dipole-dipole forces increase withincreasing polarity.


21/24


London Dispersion Forces Weakest of all intermolecular forces.

It is possible for two adjacent neutral molecules toaffect each other.

The nucleus of one molecule (or atom) attracts theelectrons of the adjacent molecule (or atom).

For an instant, the electron clouds becomedistorted.

In that instant a dipole is formed (called aninstantaneous dipole).


Ion-Induced Dipole: An ion induces a dipole moment in an adjacent

molecule or atom.

Interaction between an ion (e.g. Na+) and adipole (e.g. water).


London Dispersion Forces


London Dispersion Forces One instantaneous dipole can induce another

instantaneous dipole in an adjacent molecule (or

atom). The forces between instantaneous dipoles are

called London dispersion forces.

Polarizability is the ease with which an electroncloud can be deformed.

The larger the molecule (the greater the number ofelectrons) the more polarizable.


Polarizability & Periodic Table

Polarizability increasesdown a group of atoms orions because size increases & larger electronclouds are more easily distorted

Polarizabilitydecreases from left to right acrossa period because the effective nuclear chargeholds the electrons more tightly

Cations are less polarizable than parent atombecause they are smaller, whereas anions aremore polarizable because they are larger


22/24


London Dispersion Forces


London Dispersion Forces London dispersion forces increase as molecular weight

increases.

London dispersion forces exist between all molecules. London dispersion forces depend on the shape of the

molecule.

The greater the surface area available for contact, thegreater the dispersion forces.

London dispersion forces between spherical moleculesare lower than between sausage-like molecules.

Intermolecular ForcesHydrogen Bonding Special case of dipole-dipole forces.

By experiments: boiling points of compounds with H-F, H-O, and H-N bonds are abnormally high.

Intermolecular forces are abnormally strong.

H-bonding requires H bonded to an electronegativeelement (most important for compounds of F, O, andN). Electrons in the H-X (X = electronegative element) lie much

closer to X than H.

H has only one electron, so in the H-X bond, the + H

presents an almost bare proton to the - X. Therefore, H-bonds are strong.

Intermolecular ForcesHydrogen Bonding


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Intermolecular ForcesHydrogen Bonding Hydrogen bonds are responsible for:

Ice Floating Solids are usually more closely packed than liquids;

therefore, solids are more dense than liquids. Ice is ordered with an open structure to optimize H-bonding.

Therefore, ice is less dense than water.

In water the H-O bond length is 1.0 .

The OH hydrogen bond length is 1.8 .

Ice has waters arranged in an open, regular hexagon.

Each + H points towards a lone pair on O. Ice floats, so it forms an insulating layer on top of lakes,

rivers, etc. Therefore, aquatic life can survive in winter.


Hydrogen Bonding Hydrogen bonds are responsible for:

Protein Structure Protein folding is a consequence of H-bonding.

DNA Transport of Genetic Information


Comparing Intermolecular Forces


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Intermolecular Forces in Solutions

Ion-Dipole (40-600 kJ/mol)

H bond (10-40 kJ/mol)

Dipole-Dipole (5-25 kJ/mol)

Ion-Induced dipole (3-15 kJ/mol)

Dipole-Induced Dipole (2-10 kJ/mol)

Dispersion (0.05-40 kJ/mol)

Strongest

to

Weakest

The Uniqueness of Water Water has many unusual properties when

compared with properties that periodic trendswould otherwise predict: Higher boiling point

Higher specific heat capacity Higher surface tension, capillarity Higher heat of vaporization Lower vapor pressure Higher viscosity Dissolves many substances Liquid state at room T & P Solid form floats on liquid less dense

The electrons forming each bond betweenhydrogen and oxygen are drawn strongly toward

the oxygen atom

This results in two very polar bonds

The 104.5bond angle makes a strong dipole

Water molecules also form hydrogen bonds

Comparison of Ice and Water

Issues: H-bonds and Motion

Ice: 4 H-bonds per water molecule

Water: 2.3 H-bonds per water molecule Ice: H-bond lifetime - about 10 microsec

Water: H-bond lifetime - about 10 psec

(10 psec = 0.00000000001 sec)

Thats "one times ten to the minus elevensecond"!

Slide 2 Matter and Properties of Matter

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