Covalent Bonding
description
Transcript of Covalent Bonding
COVALENT BONDING
Chemistry Matter and Change Chapter 8
CHAPTER 8 MAIN IDEA
Covalent bonds form when atoms share electrons.
Atoms gain stability when
they share electrons and form covalent
bonds.
8.1
Main
Idea
REVIEW VOCABULARY & CONCEPTS
Chemical bondValence electronsElectronegativityLewis structure
NEW VOCABULARY & CONCEPTS
Covalent bondMoleculeSigma (σ)bondPi (π)bondEndothermic reactionExothermic reactionSingle bondDouble bondTriple bond
WHY DO ATOMS BOND?Sharing electrons takes less energy than being “alone”
Octet is usually the most stable electron configuration
WHAT IS A COVALENT BOND?
Shared pairs of electronshttp://www.glencoe.com/sites/
common_assets/science/cmc/cim/animations/ch8_3_1.swf
SINGLE COVALENT BONDS Two atoms share one pair of electrons
Sigma bond (σ)Either : or _ for a Lewis Structure H H·+· ··H H or H-H
MULTIPLE COVALENT BONDS
Two atoms share more than one pair of electrons
One pair is a sigma bond (σ)the others are pi (π)bonds
Double bond shares 2 pair of electrons
Triple bond shares 3 pair of electrons
COMPARING BONDS
SingleCentereds orbital
electrons One pair of
electrons is shared
PairedParallel p orbital
electronsMultiple pairs
of electrons are shared
Sigma (σ) Bonds
Pi (π) Bonds
MOLECULEφ A neutral group of atoms joined together by covalent bonds.
DIATOMIC MOLECULESφ Molecules made up of two atoms.
φ There are 7 diatomic molecules.
φ H2, N2, O2, F2, Cl2, Br2, I2
Br I N Cl H O F
DIATOMIC MOLECULES
Oh, Ha Ha!
I couldn't exist
without you!
HYDROGEN
H· + ·H H:HHydrogen Hydrogen Hydrogen
Atom Atom molecule
φ The hydrogen molecule has a single covalent bond.
φ The electronegativity of each hydrogenatom is the same, so the electrons are shared.
Shared electron pair
MOLECULAR COMPOUNDS
φ Compounds comprised of molecules.
Ionic Compounds Molecular Compounds
Crystal Lattice Molecule
Types of Elements
Metal with non-metal or polyatomic ions
Non-metal with non-metal
Physical State
Solid Solid, liquid or gas
Melting Point High> 300 C
Low <300 C
Solubility in water
Generally high Generally low
Electrical conductivity of solution
Good conductor Poor to none
VIDEOhttp://www.glencoe.com/sites/
common_assets/science/cmc/cim/animations/ch8_1.swf
LEWIS STRUCTURES AND OCTET
Practice by drawingH2
O2
N2
H2OCO2
+ +-
-
LEWIS STRUCTURES AND OCTET
Practice by drawingH2
+ +-
-
LEWIS STRUCTURES AND OCTET
Practice by drawing O2
++
-
--
-
-
-
-
-
- -
--
π
σ
+
-
- -
--
+-
-
-
-
---
STRENGTH OF COVALENT BONDS
Strength depends on distance of the atoms from each other
With more bonds comes stronger bonds
O2 is stronger than H2
single bond < Double
bond < Triple bond
22
CHEMICAL BONDS
23
CHEMICAL BONDSElectronegativity is an atom’s affinity
for electrons.
Differences in electronegativity dictate how electrons are distributed in covalent bonds.
- nonpolar covalent bonds = equal sharing of electrons
- polar covalent bonds = unequal sharing of electrons
BONDS AND ENERGYEndothermic reactions require additional energy for bonds to break
Exothermic reactions release energy when the bonds break (spontaneous)
NAMING MOLECULES
Section 8.2 Chemistry Matter & Change
Specific rules are used when
naming binary molecular
compounds, binary acids and
oxyacids
8.2
Main
Idea
OBJECTIVESTranslate molecular formulas into binary molecular names.
Name acidic solutions.
REVIEW VOCABULARY & CONCEPTS
Ionic bondCovalent bondFormula unitOxyanionNaming ionic substancesMolecule
NEW VOCABULARY & CONCEPTS
OxyacidBinary acid
NAMING BINARY MOLECULAR
COMPOUNDS1. Name the first element
using the entire name of the element.
2. The second element in the formula is named using the root and suffix “-ide.”
3. Prefixes are used to indicate the numbers of each element.
COMMON PREFIXESNumber of atoms
PrefixNumber of atoms
Prefix
1 Mono- 6 Hexa-2 Di- 7 Hepta-3 Tri- 8 Octa-4 Tetra- 9 Nona-5 Penta- 10 Deca-
NAMING BINARY MOLECULAR
COMPOUNDSExceptions to the rules:The first element never uses “mono-” There is an understood 1 if
nothing is specified.Awkward vowels can be dropped
NAMING BINARY MOLECULAR
COMPOUNDS EXCEPTION The first element never uses
“mono-” There is an understood 1 if
nothing is specified. CO2 is carbon dioxide not
monocarbon dioxide CO is carbon monoxide, not
monocarbon monoxide
PRACTICE NAMING BINARY COMPOUNDS
FORMULA SYSTEM NAME
N2O dinitrogen monoxide
NO nitrogen monoxide
N2O3 dinitrogen trioxide
NO2 nitrogen dioxide
N2O4 dinitrogen tetroxide
N2O5 dinitrogen pentoxide
NO3 nitrogen trioxide
NAMING BINARY ACIDSThe first word has the prefix “hydro-” followed by the root of the second element followed by “-ic”
The second word is “acid”HCl- hydrochloric acid
PRACTICE NAMING BINARY ACIDS
Hydrobromic acidHydrophosphic acidHydrosulfuric acidHFH2SeHI
NAMING OXYACIDSFirst word consists of the root of the
oxyanion (with prefixes if needed) followed by a suffix as specified
If oxyanion ends in
The second word is always “acid.”
Oxyanion ending New suffix for acid
-ate -ic
-ite -ous
NAMING OXYACIDSRelationship
General name
Oxyanion name
Example name
Example formula
One more oxygen than (root)ic
Per(root)ic acid Perchlorate Perchloric
acidHClO4
Root(ic) acid chlorate Chloric acid HClO3
One less oxygen than root(ic)
Root(ous) acid Chlorite Chlorous
acidHClO2
Two less oxygens than root(ic)
Hypo(root)ous acid
Hypochlorite
Hypochlorous acid HClO
NAMING OXYACIDSFirst word consists of the root of the
oxyanion (with prefixes if needed) followed by a suffix as specified
The second word is always “acid.”
Compound Oxyanion Acid suffix Acid name
HClO3 Chlorate -ic Chloric acid
HClO2 Chlorite -ous Chlorous acid
HNO3 Nitrate -ic Nitric Acid
HNO2 Nitrite -ous Nitrous Acid
Look at the formula of the
molecule
Is there oxygen present in the compound?
Hydro(root) ic acid
Root + -ic if the anion ends in –ate, or
Root + -ous if the anion ends in –ite, then
acid
Name the first element using a prefix if necessaryName the second element indicating the number of atoms and changing the
suffix to –ide.
YesNo
YesNo
Is it an acid?
Acid Formula Acid Name
H2CO3 Carbonic Acid
HBrO3 Bromic Acid
H2C Carbonic Acid
CH3COOH or CH3CO2H Acetic acid
H3PO4 Phosphoric acid
H2SO4 Sulfuric acid
H2SO3 Sulfurous Acid
PRACTICE NAMING OXYACIDS
CAN YOUTranslate molecular formulas into binary molecular names.
Name acidic solutions.
MOLECULAR STRUCTURE
Section 8.3 Chemistry Matter & Change
Structural formulas show
the relative positions of
atoms within a molecule.
8.3
Main
Idea
OBJECTIVESList the basic steps used to draw Lewis structures.
Explain why resonance occurs and identify resonance structures.
Identify three exceptions to the octet rule and name molecules in which these exceptions occur.
REVIEW VOCABULARY & CONCEPTS
Ionic bondCovalent bondLewis-dot structureOctet
NEW VOCABULARY & CONCEPTS
Structural formulaResonanceCoordinate covalent bondSpace filling modelBall and stick model
MOLECULAR STRUCTURES
Many different ways to depict the same thingMolecular formulaStructural formulaLewis StructureSpace-filling modelBall-and-stick model
MOLECULAR FORMULAIndicates number of each element in a molecule H2O C6H12O6
NH3
STRUCTURAL FORMULASMolecular model that shows the relative positions of the atoms
O H H
LEWIS STRUCTUREShows shared electrons and lone pairsShared pairs are usually
depicted as linesLone pairs may be lines or dots
SPACE-FILLING MODELAtoms are shown in relative size and position accounting for lone pairs
BALL AND STICK MODELSShow relative position of atoms and bondsEasier to see double and triple
bonds and bond angles
HINTS FOR LEWIS STRUCTURES
1. Carbon is usually in the middle
2. Group 1 and 17 elements are always at ends
3. Atoms that are less numerous are usually in the middle
(~Polyatomic Ions)
SIMPLE PRACTICE FOR LEWIS STRUCTURES
H2OHClCH3F
ORGANIC PRACTICE WITH LEWIS STRUCTURES
Methane CH4
Ethane C2H6
Propane C3H8
TRICKIER PRACTICECO2
HCNBH3
NH4+
TRICKIER ORGANIC PRACTICE
C2H6 ethaneC2H4 etheneC2H2 ethyne
RESONANCE STRUCTURES
More than one valid Lewis structure is possibleDiffer in position of electrons,
not position of atoms
HINTS FOR FORMING LEWIS STRUCTURES
Carbon is usually in the middle Group 1 and 17 elements are always at ends Atoms that are less numerous are usually in the
middle Hydrogen always forms one single bond Oxygen has two bonding electrons and two lone
pairs Nitrogen has three bonding electron and one lone
pair Group 13 elements have three bonding electrons
and zero lone pairs Elements in groups 1, 2, 13 may break octet by
having fewer electrons Phosphorus is a mess!
REALLY HARDPCl5SF6
ORGANIC CHEATS Common groups are often listed differently in organic molecules
Ex: we write NH2CH2COOH instead of C2NO2H5
CAN YOUList the basic steps used to draw Lewis structures.
Explain why resonance occurs and identify resonance structures.
Identify three exceptions to the octet rule and name molecules in which these exceptions occur.
MOLECULAR SHAPES
Section 8.4 Chemistry Matter and Change
The VSEPR model is used to
determine molecular shape
Main
Idea
OBJECTIVESSummarize VSEPR bonding theory
Predict the shape of, and bond angles in, a molecule
Define hybridization
REVIEW VOCABULARY & CONCEPTS
Atomic orbitals orbitalp orbital
NEW VOCABULARY & CONCEPTS
VSEPR theoryHybridizationTrigonal planarTrigonal pyramidalTetrahedralTrigonal bipyramidalLinearBentOctahedral
VSEPR MODELValence Shell Electron Pair Repulsion
Electrons repel each otherElectrons stay as far away from
each other as possibleLone pairs occupy more space than shared electrons
HYBRIDIZATIONOccurs because hybrid orbitals are more stable in some cases, notably carbon
Remodel the “hotel” to make the “rooms” equal
C: 1s22s22p2 1s22sp3
CARBON HYBRIDIZATION
GETTING STARTEDBegin with Lewis StructureStart with a tetrahedral and modify as needed
Remember to use 3-D space not 2-D space
VIDEOhttp://www.glencoe.com/sites/
common_assets/science/cmc/cim/animations/ch8_2.swf
CH4: A TYPICAL TETRAHEDRAL
TETRAHEDRAL SHAPEFour atoms are coming from the center atom at equal angles
109.5° angle
TRIGONAL PYRAMIDALThree atoms coming from central atom and one lone pairBond angle 107°Lone pairs occupy more space
than shared pairs
BENTTwo atoms coming from central atom and two lone pairs
104.5° bond angle
SUMMARY OF COMMON MOLECULAR SHAPES
Molecule
Total pairs
Shared pairs
Lone pairs
Hybrid orbital
Molecular shape
BeCl2 2 2 0 sp Linear
AlCl3 3 3 0 sp2 Trigonal planar
CCl4 4 4 0 sp3 Tetrahedral
NH3 4 3 1 sp3 Trigonal pyramidal
H2O 4 2 2 sp3 Bent
NbBr5 5 5 0 sp3d Trigonal bipyramidal
SF6 6 6 0 sp3d2 Octahedral
TETRAHEDRAL BASED SHAPES
TetrahedralTrigonal Pyramidal
Bent
NON-TETRAHEDRAL BASED SHAPES
Linear Trigonal Planar
FEWER ELECTRONS THAN OCTET!
NON-TETRAHEDRAL BASED SHAPES
Trigonal Bipyramidal Octahedral
MORE ELECTRONS THAN OCTET!
CAN YOU…Summarize VSEPR bonding theory
Predict the shape of, and bond angles in, a molecule
Define hybridization
ELECTRONEGATIVITY AND POLARITY
Chapter 8.5 Chemistry Matter and Change
A chemical bond’s character is
related to each atom’s attraction for the electrons
in the bond.
Main
Idea
OBJECTIVESDescribe how electronegativity is used to determine bond type.
Compare and contrast polar and nonpolar covalent bonds and polar and nonpolar molecules
Generalize about the characteristics of covalently bonded compounds
REVIEW VOCABULARY & CONCEPTS
ElectronegativityElectron affinityIonic bondCovalent bond
NEW VOCABULARY & CONCEPTS
Polar covalent bondElectronegativity differenceMolecular polarityIntermolecular forcesSolubility Dipole
ELECTRON AFFINITY, ELECTRONEGATIVITY, AND BOND
CHARACTER
Electronegativity difference
Bond Character
> 1.7 Mostly ionic
0.4 - 1.7 Polar covalent
< 0.4 Mostly covalent
0 Nonpolar covalent
Electronegativity difference determines the character of the bond between atoms
Most bonds are partly ionic and partly covalentDiatomics are 100% covalent
BOND CHARACTER
IONIC BONDSCreated when the electronegativity difference is greater than 1.7
Elements are far apart on periodic tableExample: Na and Cl
Na = 0.9Cl = 3.0Difference is 2.1 ionic bondElectrons are transferred from Na to Cl
NON-POLAR COVALENT BONDS
Created when electronegativity difference is 0Usually atoms of the same
elementDiatomics
COVALENT BONDS Created when electronegativity difference is < 0.4
Elements are usually close together on the periodic table
IBr
POLAR-COVALENT BONDS
Created when electronegativity difference is between 0.4 and 1.7
Most bonds fall into this category
Electrons are shared unequallyH2O
POLAR COVALENT BONDS Molecules have a partial positive and a partial negative side
DIPOLE INTERACTIONS Reactions between oppositely charged ends of a polar molecule
POLAR COVALENT BONDSPolar bonds that are equal in all directions in a molecule create non-polar molecules
SOLUBILITY RULESLike dissolves like
Polar substances dissolve polar substances
Non-polar substances dissolve non-polar substances.
CAN YOUDescribe how electronegativity is used to determine bond type.
Compare and contrast polar and nonpolar covalent bonds and polar and nonpolar molecules
Generalize about the characteristics of covalently bonded compounds