types of chemical bonds
DESCRIPTION
Types of chemical bonds. Bond : Force that holds groups of two or more atoms together and makes the atoms function as a unit. Example: H-O-H Bond Energy : Energy required to break a bond. Ionic Bond : Attractions between oppositely charged ions. - PowerPoint PPT PresentationTRANSCRIPT
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Types of chemical bondsTypes of chemical bonds
BondBond: Force that holds groups of two or more atoms together and : Force that holds groups of two or more atoms together and makes the atoms function as a unit.makes the atoms function as a unit.
Example: H-O-HExample: H-O-H
Bond EnergyBond Energy: Energy required to break a bond.: Energy required to break a bond.
Ionic BondIonic Bond: Attractions between oppositely charged ions.: Attractions between oppositely charged ions.
Example: NaExample: Na+ + ClCl--
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Types of chemical bondsTypes of chemical bonds
Ionic CompoundIonic Compound: A compound resulting from a positive ion : A compound resulting from a positive ion (usually a metal) combining with a negative ion (usually a (usually a metal) combining with a negative ion (usually a non-metal).non-metal).
Example: MExample: M++ + X + X-- MX MX
Covalent BondCovalent Bond: Electrons are shared by nuclei.: Electrons are shared by nuclei.
Example: H-HExample: H-H
Polar Covalent BondPolar Covalent Bond: Unequal sharing of electrons by nuclei.: Unequal sharing of electrons by nuclei.
Example: H-FExample: H-F
Hydrogen fluoride is an example of a molecule that has bond Hydrogen fluoride is an example of a molecule that has bond polarity.polarity.
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Lewis structuresLewis structures
Lewis StructureLewis Structure: Representation of a molecule that shows : Representation of a molecule that shows how the valence electrons are arranged among the atoms how the valence electrons are arranged among the atoms in the molecule.in the molecule.
Bonding involves the valence electrons of atoms.Bonding involves the valence electrons of atoms.
Example: NaExample: Na●● H-H H-H
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Lewis structures of Lewis structures of elementselements Dots around elemental symbolDots around elemental symbol
– Symbolize valence electronsSymbolize valence electrons Thus, one must know valence electron Thus, one must know valence electron
configurationconfiguration
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Lewis Structures of Lewis Structures of moleculesmoleculesSingle BondSingle Bond: Two atoms sharing one electron pair.: Two atoms sharing one electron pair.
Example: HExample: H22
Double BondDouble Bond: Two atoms sharing two pairs of electrons.: Two atoms sharing two pairs of electrons.
Example: OExample: O22
Triple BondTriple Bond: Two atoms sharing three pairs of electrons.: Two atoms sharing three pairs of electrons.
Example: NExample: N22
Resonance StructuresResonance Structures: More than one Lewis Structure can be drawn : More than one Lewis Structure can be drawn for a molecule.for a molecule.
Example: OExample: O33
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Rules for Lewis structures of Rules for Lewis structures of moleculesmolecules1.1. Write out valence electrons for each Write out valence electrons for each
atomatom2.2. Connect lone electrons because lone Connect lone electrons because lone
electrons are destabilizingelectrons are destabilizing1.1. Become two shared electronsBecome two shared electrons
1.1. Called a “bond”Called a “bond”
3.3. Check to see if octet rule is satisfiedCheck to see if octet rule is satisfied1.1. Recall electron configuration resembling Recall electron configuration resembling
noble gasnoble gas1.1. In other words, there must be 8 electrons In other words, there must be 8 electrons
(bonded or non-bonded) around atom(bonded or non-bonded) around atom1.1. Non-bonded electron-pair Non-bonded electron-pair
1.1. Called “lone pair”Called “lone pair”
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Let’s do some examples Let’s do some examples on the boardon the board HH22
– Duet ruleDuet rule
FF22
– Octet ruleOctet rule
OO22
NN22
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Lewis structuresLewis structures
ExampleExample
Write the Lewis Structure for the following molecules:Write the Lewis Structure for the following molecules:
1)1) HH22OO
2)2) CClCCl44
1)1) Where does the carbon go & why?Where does the carbon go & why?
3)3) PHPH33
4)4) HH22SeSe
5)5) CC22HH66
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Lewis structures Lewis structures continuedcontinued6)6) COCO22
7)7) CC22HH44
8)8) CC22HH22
9)9) SiOSiO22
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Polyatomic ionsPolyatomic ions
If positive charge on ion If positive charge on ion Take away electron from central speciesTake away electron from central species
If negative charge on ionIf negative charge on ion Add electron to central speciesAdd electron to central species
Example:Example: HH33OO++
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Your turnYour turn
NHNH44++
ClOClO--
OHOH--
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Resonance structuresResonance structures
When structures can be written in When structures can be written in more than one waymore than one way– OO33
Actual molecule is “in-between”Actual molecule is “in-between”– Resonance hybridResonance hybrid
Another exampleAnother example– HCOHCO33
--
What would its resonance hybrid look What would its resonance hybrid look like?like?
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Practice Practice
NONO22--
NONO33--
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Practice Practice
HH22OO22
HH33OO++
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Aberrant compoundsAberrant compounds
Odd-electron speciesOdd-electron species– NONO
– NONO22
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Aberrant compoundsAberrant compounds
Incomplete octetIncomplete octet– BHBH33
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Aberrant compoundsAberrant compounds
Expanded octetExpanded octet– Some central atoms can exceed an Some central atoms can exceed an
octetoctet Third period and higher elements Third period and higher elements
can do thiscan do this– E.g., Al, Si, P, S, Cl, As, Br, Xe, etc.E.g., Al, Si, P, S, Cl, As, Br, Xe, etc.– d-orbitals can accommodate extra d-orbitals can accommodate extra
electronselectrons
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ExamplesExamples
AsIAsI55
XeFXeF22
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Practice Practice
SClSCl66 XeFXeF44
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Practice Practice
SOSO332-2-
POPO333-3-
SOSO22
SOSO33
HH22SeOSeO44
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ElectronegativityElectronegativity
ElectronegativityElectronegativity: The relative ability of an atom in a : The relative ability of an atom in a molecule to attract shared electrons to itself.molecule to attract shared electrons to itself.
Example: Fluorine has the highest electronegativity.Example: Fluorine has the highest electronegativity. SimilarSimilar electronegativities between elements give non- electronegativities between elements give non-
polar covalent bonds (0.0-0.4)polar covalent bonds (0.0-0.4) DifferentDifferent electronegativities between elements give electronegativities between elements give
polar covalent bonds (0.5-1.9)polar covalent bonds (0.5-1.9) If the difference between the electronegativities of two If the difference between the electronegativities of two
elements is about 2.0 or greater, the bond is ionicelements is about 2.0 or greater, the bond is ionic
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ElectronegativityElectronegativity
ExampleExample
For each of the following pairs of bonds, For each of the following pairs of bonds, choose the bond that will be more polar.choose the bond that will be more polar.
Al-P vs. Al-NAl-P vs. Al-N C-O vs. C-SC-O vs. C-S
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Dipole momentDipole moment
Dipole Moment Dipole Moment A molecule that has a center of positive A molecule that has a center of positive
charge and a center of negative chargecharge and a center of negative charge Will line up on electric fieldWill line up on electric field
In Debye unitsIn Debye units 1 D = 3.34 x 101 D = 3.34 x 10-30-30 C C m m
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Examples Examples
FF22
COCO22
HH22OO
NHNH33
BFBF33
CClCCl44
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Molecular polarityMolecular polarity
Net-dipole moment leads to Net-dipole moment leads to molecular polaritymolecular polarity
Thus the following two that have Thus the following two that have net-dipole moments are polar:net-dipole moments are polar:– HH22OO
– NHNH33
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Molecular structureMolecular structure
Molecular StructureMolecular Structure: or geometric structure refers to the : or geometric structure refers to the three-dimensional arrangement of the atoms in a three-dimensional arrangement of the atoms in a molecule.molecule.
Bond AngleBond Angle: The angle formed between two bonds in a : The angle formed between two bonds in a molecule.molecule.
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Molecular structure:Molecular structure:VSEPRVSEPRThe VSEPR ModelThe VSEPR Model: The valence shell electron pair : The valence shell electron pair
repulsion model is useful for predicting the molecular repulsion model is useful for predicting the molecular structures of molecules formed from nonmetals.structures of molecules formed from nonmetals.
The structure around a given atom is determined by The structure around a given atom is determined by minimizing repulsions between electron pairs.minimizing repulsions between electron pairs.
The bonding and nonbonding electron pairs (lone pairs) The bonding and nonbonding electron pairs (lone pairs) around a given atom are positioned as far apart as around a given atom are positioned as far apart as possible.possible.
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Molecular Structure:Molecular Structure:VSEPRVSEPRSteps for Predicting Molecular Structure Using the VSEPR Steps for Predicting Molecular Structure Using the VSEPR
ModelModel
1. Draw the Lewis structure for the molecule.1. Draw the Lewis structure for the molecule.
2. Count the electron pairs and arrange them in the way 2. Count the electron pairs and arrange them in the way that minimizes repulsion (that is, put the lone pairs as that minimizes repulsion (that is, put the lone pairs as far apart as possible).far apart as possible).
3. Determine the positions of the atoms from the way the 3. Determine the positions of the atoms from the way the electron pairs are shared.electron pairs are shared.
4. Determine the name of the molecular structure from the 4. Determine the name of the molecular structure from the positions of the atoms.positions of the atoms.
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Example Example
BrBr22
COCO22
CFCF44
PFPF33
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Your turnYour turn
NHNH44++
XeFXeF44
AsIAsI55
SFSF3 3 ++
II3 3 --