slide 2 matter and properties of matter
TRANSCRIPT
-
8/8/2019 Slide 2 Matter and Properties of Matter
1/24
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)
-
8/8/2019 Slide 2 Matter and Properties of Matter
2/24
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
-
8/8/2019 Slide 2 Matter and Properties of Matter
3/24
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
-
8/8/2019 Slide 2 Matter and Properties of Matter
4/24
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
-
8/8/2019 Slide 2 Matter and Properties of Matter
5/24
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
-
8/8/2019 Slide 2 Matter and Properties of Matter
6/24
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
-
8/8/2019 Slide 2 Matter and Properties of Matter
7/24
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
Chlorides of Period 2
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
Chlorides of Period 3
00.600.61.11.62.2EN
Cl2OCl2NCl3CCl4BCl3BeCl2LiClcompound
Chlorides of Period 2
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.
-
8/8/2019 Slide 2 Matter and Properties of Matter
8/24
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
-
8/8/2019 Slide 2 Matter and Properties of Matter
9/24
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
Chlorides of Period 3
-102-121-40-23-107415610melting point
Cl2OCl2NCl3CCl4BCl3BeCl2LiClcompound
Chlorides of Period 2
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
Chlorides of Period 3
00.600.61.11.62.2EN
Cl2OCl2NCl3CCl4BCl3BeCl2LiClcompound
Chlorides of Period 2
large difference small difference
The electronegativity difference - EN = ENhigher EN lower
-
8/8/2019 Slide 2 Matter and Properties of Matter
10/24
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
-
8/8/2019 Slide 2 Matter and Properties of Matter
11/24
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
-
8/8/2019 Slide 2 Matter and Properties of Matter
12/24
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
-
8/8/2019 Slide 2 Matter and Properties of Matter
13/24
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
-
8/8/2019 Slide 2 Matter and Properties of Matter
14/24
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.
-
8/8/2019 Slide 2 Matter and Properties of Matter
15/24
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
-
8/8/2019 Slide 2 Matter and Properties of Matter
16/24
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
-
8/8/2019 Slide 2 Matter and Properties of Matter
17/24
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.
-
8/8/2019 Slide 2 Matter and Properties of Matter
18/24
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
-
8/8/2019 Slide 2 Matter and Properties of Matter
19/24
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
-
8/8/2019 Slide 2 Matter and Properties of Matter
20/24
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 =
Intermolecular Forces
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.
-
8/8/2019 Slide 2 Matter and Properties of Matter
21/24
Intermolecular Forces
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).
Intermolecular Forces
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).
Intermolecular Forces
London Dispersion Forces
Intermolecular 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.
Intermolecular Forces
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
-
8/8/2019 Slide 2 Matter and Properties of Matter
22/24
Intermolecular Forces
London Dispersion Forces
Intermolecular 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
-
8/8/2019 Slide 2 Matter and Properties of Matter
23/24
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.
Intermolecular Forces
Hydrogen Bonding Hydrogen bonds are responsible for:
Protein Structure Protein folding is a consequence of H-bonding.
DNA Transport of Genetic Information
Intermolecular Forces
Comparing Intermolecular Forces
-
8/8/2019 Slide 2 Matter and Properties of Matter
24/24
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"!