the chemical bond. chemical bonds are the forces that hold atoms together to form compounds bond...
Post on 29-Dec-2015
221 Views
Preview:
TRANSCRIPT
The Chemical BondThe Chemical Bond
Chemical BondsChemical Bonds
Are the forces that hold atoms together to Are the forces that hold atoms together to form compoundsform compounds
Bond energy – the amount of energy Bond energy – the amount of energy needed to break a bond and produce a needed to break a bond and produce a neutral atomneutral atom
Bond strength – the amount of force Bond strength – the amount of force holding two atoms togetherholding two atoms together Ex. 85.9 kcal/moleEx. 85.9 kcal/mole
Types of BondsTypes of Bonds
Ionic Bond – involves the transfer of electrons Ionic Bond – involves the transfer of electrons between atomsbetween atoms
Covalent Bond – involves that sharing of Covalent Bond – involves that sharing of electrons between atomselectrons between atoms Types of Covalent bondsTypes of Covalent bonds
• Single C:CSingle C:C• Double C::CDouble C::C• Triple C:::CTriple C:::C
Coordinate Covalent Bond – one atoms donates Coordinate Covalent Bond – one atoms donates a pair of electrons to be shareda pair of electrons to be shared
Ionic BondsIonic Bonds
Involves electron transfer and ion formationInvolves electron transfer and ion formation Cation – has a positive chargeCation – has a positive charge Anion – has a negative chargeAnion – has a negative charge The cation is much smaller than the anionThe cation is much smaller than the anion In an ionic solid ions pack together in a way that In an ionic solid ions pack together in a way that
is dependant of the size of the ionsis dependant of the size of the ions Ions arrange in a way that there is local Ions arrange in a way that there is local
neutralityneutrality High melting point crystalline solidsHigh melting point crystalline solids
Electron Transfer / Ion FormationElectron Transfer / Ion Formation
Ionic BondIonic Bond
Metallic BondsMetallic Bonds
The force of attraction that holds metals The force of attraction that holds metals togethertogether
It consists of the attraction of free-floating It consists of the attraction of free-floating valence electrons for positively charged valence electrons for positively charged metal ionsmetal ions
MetalsMetals
The valence electrons of metal atoms can The valence electrons of metal atoms can be modeled as a sea of electronsbe modeled as a sea of electrons
Properties of MetalsProperties of Metals(due to the ‘sea’ of electrons)(due to the ‘sea’ of electrons)
Conduct electricity – flow of electronsConduct electricity – flow of electrons
Malleable – hammered into sheetsMalleable – hammered into sheets
Ductile – draw into wireDuctile – draw into wire
Ionic Crystal StructureIonic Crystal Structure
Note: the smaller size of the cations relative to the anions. The packing of the ions determines crystal shape.
Covalent BondCovalent Bond
Interatomic forces are created by the Interatomic forces are created by the sharing of electronssharing of electrons..
The atoms share their s and p electrons to The atoms share their s and p electrons to attain the electron configuration of a noble attain the electron configuration of a noble gasgas
Atoms have small differences in Atoms have small differences in electronegativityelectronegativity
Generally low melting points (many are Generally low melting points (many are liquids and gases at room temperature)liquids and gases at room temperature)
The Octet RuleThe Octet Rule
Atoms react by gaining or losing electrons Atoms react by gaining or losing electrons so as to acquire the stable electron so as to acquire the stable electron configuration of a noble gas. Usually eight configuration of a noble gas. Usually eight valence electronsvalence electrons
Lewis Dot StructuresLewis Dot Structures
Bond FormationBond Formation
A bond forms when two electron clouds A bond forms when two electron clouds overlap and occupy a common orbital overlap and occupy a common orbital (molecular orbital)(molecular orbital)
Overlap of ‘s’ and ‘p’ orbitalsOverlap of ‘s’ and ‘p’ orbitals
s, s overlap
s, p overlap
p, p overlap
Sigma Bonds Pi Bonds
p, p side by side overlap
Nonpolar Covalent BondsNonpolar Covalent Bonds
When the electrons are equally shared the bond When the electrons are equally shared the bond between the atoms is nonpolar. Note the even between the atoms is nonpolar. Note the even distribution of the electron cloud of the hydrogen distribution of the electron cloud of the hydrogen moleculemolecule
Polar Covalent BondsPolar Covalent Bonds
Polar – an unsymmetrical distribution of Polar – an unsymmetrical distribution of electric charge due to the unequal sharing electric charge due to the unequal sharing of electonsof electons
The electronegativity difference between The electronegativity difference between the atoms determines the degree of the atoms determines the degree of polaritypolarity
What Type of Bond Is It?What Type of Bond Is It?
Electronegativity Electronegativity DifferenceDifference
Most Probably Most Probably Type of BondType of Bond
ExampleExample
0.0 – 0.40.0 – 0.4 Nonpolar CovalentNonpolar Covalent H-HH-H
0.4-1.00.4-1.0
Moderately Polar Moderately Polar CovalentCovalent H-ClH-Cl
1.0-2.01.0-2.0
Very Polar Very Polar CovalentCovalent H-FH-F
>> 2.0 2.0 IonicIonic NaClNaCl
Classifying CompoundClassifying Compound
Molecular – held together with Molecular – held together with covalent bondscovalent bonds
Network Solid (Ionic) – held together Network Solid (Ionic) – held together with ionic bondswith ionic bonds
Dipole MomentDipole Moment
The measure of the force exerted on a The measure of the force exerted on a dipole ( a single bond)dipole ( a single bond)
DipoleDipole
A molecule that has an uneven distribution A molecule that has an uneven distribution of charge even though the molecule as a of charge even though the molecule as a whole is electrically neutralwhole is electrically neutral
The Water MoleculeThe Water MoleculeA Polar MoleculeA Polar Molecule
There are two polar covalent bonds and the bent shape of the molecule causes the uneven distribution of charge resulting in a polar molecule.
The Methane MoleculeThe Methane Molecule
The even distribution of the charge results in a nonpolar molecule
Non-polar MoleculesNon-polar Molecules
The individual C-O bonds are polar in nature but the The individual C-O bonds are polar in nature but the overall molecule is nonpolar due to the even or balanced overall molecule is nonpolar due to the even or balanced distribution of charge.distribution of charge.
Another ExampleAnother Example
The CFThe CF44 molecule has 4 evenly distributed polar molecule has 4 evenly distributed polar
bonds resulting in no net dipole for the molecule. bonds resulting in no net dipole for the molecule. The result is a nonpolar molecule The result is a nonpolar molecule
Coordinate Covalent BondCoordinate Covalent Bond
Also known as a “Dative Bond”Also known as a “Dative Bond” A covalent bond in which both electrons A covalent bond in which both electrons
are donated by a single atomare donated by a single atom
Expressions of Chemical FormulasExpressions of Chemical Formulas
Chemical formula HChemical formula H22
Lewis Dot structure (dots represent Lewis Dot structure (dots represent valence electrons) H:Hvalence electrons) H:H
Dash formula H-H (dash represents a pair Dash formula H-H (dash represents a pair of electrons –a bond)of electrons –a bond)
Electron Dot FormulasElectron Dot Formulas
Let Us Practice Some Lewis Dot Let Us Practice Some Lewis Dot Structures!Structures!
Water HWater H22OO
Methane CHMethane CH44
Ammonia NHAmmonia NH33
Carbon Tetrachloride CClCarbon Tetrachloride CCl44
Let’s see how we did!Let’s see how we did!
WaterMethane
Ammonia Carbon Tetrachloride
Some Common Molecular ShapesSome Common Molecular Shapes
LinearLinear
BentBent
PyramidalPyramidal
TetrahedralTetrahedral
Bonding and Molecular OrbitalsBonding and Molecular Orbitals
Sigma BondsSigma Bonds Single bondsSingle bonds
• Overlap of two s orbitals Overlap of two s orbitals • Overlap of an s and a p orbitalOverlap of an s and a p orbital
Pi BondsPi Bonds Double or Triple bondsDouble or Triple bonds
• Side by side interaction of two p orbitalsSide by side interaction of two p orbitals
Sigma Bonds (Sigma Bonds (
When two atomic orbitals combine to When two atomic orbitals combine to form a molecular orbital along the form a molecular orbital along the internuclear axisinternuclear axis
When two carbon atoms bond there is an overlap of atomic orbitalsalong the internuclear axis.
When carbon bonds with the hydrogens there is an overlap of hydrogen’s ‘s’ orbitals with carbons atomic orbitals to produce 6 sigma bonds.
Ethane C2H6
Pi Bonds (Pi Bonds (
When two atomic orbitals combine to form When two atomic orbitals combine to form a molecular orbital above and below the a molecular orbital above and below the internuclear axisinternuclear axis
Can result from the side by side interaction Can result from the side by side interaction between two ‘p’ orbitals between two ‘p’ orbitals
The Carbon Carbon Double BondC=C
Consists on one and one bond
So why does carbon bond with 4 So why does carbon bond with 4 equal energy orbitals?equal energy orbitals?Why does carbon form Why does carbon form tetrahedral geometry?tetrahedral geometry?
Answer:Answer:
Hybrid Orbital TheoryHybrid Orbital Theory
Carbons 1-s and 3-p valence orbitals combine to result in 4 equal energy bonding orbitals
The four equal energy orbitals account for carbons tetrahedral geometry
spsp22 Hybridization in Boron Hybridization in Boron
Results in trigonal planar geometry
sp Hybridization in sp Hybridization in BerylliumBeryllium
Explains linear geometryExplains linear geometry
Molecular Shapes Molecular Shapes
LinearLinear
BentBent
PyramidalPyramidal
Trigonal PlanarTrigonal Planar
TetrahedralTetrahedral
Energy Changes in Bond FormationEnergy Changes in Bond FormationBonding and Antibonding OrbitalsBonding and Antibonding Orbitals
* Notice that the molecular orbital is lower
energy then the atomic orbitals
The energy levels in a hydrogen molecule can be represented in a diagram - showing how the two 1s atomic orbitals combine to form two molecular orbitals, one bonding () and one antibonding (*)
top related