iv. lesson essential questions: › why do atoms form chemical bonds? › how is the type of...
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IV
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Lesson Essential Questions:› Why do atoms form chemical bonds?› How is the type of chemical bond
determined?
Vocabulary: chemical bond, ionic bonding, covalent bonding, nonpolar-covalent bonding, polar, polar-covalent bonding
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Chemical Bond
› attractive force between atoms or ions that binds them together as a unit
› bonds form in order to… decrease potential energy (PE) increase stability
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ION
PolyatomicIon
MonatomicIon
1 atom 2 or more atoms
NONO33--NaNa++
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IONIC COVALENTBond Formation
Type of Structure
Solubility in Water
Electrical Conductivity
OtherProperties
e- are transferred from metal to nonmetal
high
yes (solution or liquid)
yes
e- are shared between two nonmetals
low
no
usually not
MeltingPoint
crystal lattice true molecules
Physical State solid Solid, liquid, or gas
odorous
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“electron sea”
METALLICBond Formation
Type of Structure
Solubility in Water
Electrical Conductivity
OtherProperties
MeltingPoint
Physical State
e- are delocalized among metal atoms
very high
yes (any form)
no
malleable, ductile, lustrous
solid
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Ionic Bonding - Crystal Lattice
RETURN
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Covalent Bonding - True Molecules
RETURN
Diatomic Molecule
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Metallic Bonding - “Electron Sea”
RETURN
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Most bonds are a blend of ionic and covalent characteristics.
Difference in electronegativity determines bond type.
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Electronegativity› Attraction an atom has for a shared pair of
electrons.› higher e-neg atom -
› lower e-neg atom +
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Electronegativity Trend› Increases up and to the right.
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Nonpolar Covalent Bond› e- are shared equally› symmetrical e- density› usually identical atoms
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+ -
Polar Covalent Bond› e- are shared unequally› asymmetrical e- density› results in partial charges (dipole)
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Nonpolar
Polar
Ionic
View Bonding Animations.
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Examples:
Cl2
HCl
NaCl
3.0-3.0=0.0Nonpolar
3.0-2.1=0.9Polar
3.0-0.9=2.1Ionic
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What type of bonding would be expected between the following atoms?› Li and Cl› Ca and Ga› I and Cl› K and Na
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Lesson Essential Questions:› How is a molecular compound formed?› What are some of the characteristics of a
covalent bond?
Vocabulary: molecule, chemical formula, molecular formula, bond energy, electron-dot, Lewis structure, structural formula, single bond, multiple bonds, resonance
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Covalent bond – bond that is created by the sharing of electrons
Molecule – neutral group of atoms held together by covalent bonds
Molecular compound – chemical compound made of molecules
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CHEMICAL FORMULA
MolecularFormula
FormulaUnit
IONIC COVALENT
COCO22NaClNaCl
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Potential Energy› based on position of an object› low PE =
high stability
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no interaction
attraction vs. repulsion
increased attraction
Potential Energy Diagram
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balanced attraction & repulsion
increased repulsion
attraction vs. repulsion
Potential Energy Diagram
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Bond Energy
Bond Energy› Energy required to break a bond
Bond Length
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Bond Energy› Short bond = high bond energy
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Electron Dot Diagrams1. Pick the central atom2. Count the valence electrons (they are
what electron dot diagrams show)3. Place electrons around the atom
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Octet Rule› Most atoms form bonds in order to obtain 8
valence e-
› Full energy level stability ~ Noble Gases
Ne
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+ -
+
Nonpolar Covalent - no charges
Polar Covalent - partial charges
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On page 186 in your text book do practice problems #1-4
1. Draw the Lewis structure of ammonia, NH3
2. Draw the Lewis structure for hydrogen sulfide, H2S
3. Draw the Lewis structure for silane, SiH4
4. Draw the Lewis structure for phosphorus trifluoride, PF3
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Some elements can share more than one electron pair.› Double bond (two pairs of electrons are
shared)› Triple bond (three pairs of electrons are
shared)
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Draw Lewis structures for each of the following molecules:› O2
› CO2
› N3
› N2
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Occurs when more than one valid Lewis structure can be written for a particular molecule (due to position of double bond)
•These are resonance structures of benzene.
•The actual structure is an average (or hybrid)
of these structures.
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Neither structure is correct, it is actually a hybrid
of the two. To show it, draw all varieties
possible, and join them with a double-headed
arrow.
Note the different location of the
double bond
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Resonance in
a carbonate ion
(CO32-):
Resonance in
an acetate ion
(C2H3O21-):
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Prefix System (binary compounds)
1. Less e-neg atom comes first.
2. Add prefixes to indicate # of atoms. Omit mono- prefix on first element.
3. Change the ending of the second element to -ide.
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PREFIXmono-di-tri-tetra-penta-hexa-hepta-octa-nona-deca-
NUMBER12345678910
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CCl4
N2O
SF6
carbon tetrachloride
dinitrogen monoxide
sulfur hexafluoride
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arsenic trichloride
dinitrogen pentoxide
tetraphosphorus decoxide
AsCl3
N2O5
P4O10
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Lesson Essential Questions:› How is an ionic bond formed?› What are some of the characteristics of an
ionic bond?
Vocabulary: ionic compound, formula unit, lattice energy, polyatomic ion
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Ionic compound – composed of positive and negative ions that are combined so that the charges are equal.
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CHEMICAL FORMULA
MolecularFormula
FormulaUnit
IONIC COVALENT
COCO22NaClNaCl
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Electron dot notation is used to note changes.
Form to create an atmosphere of stability
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Covalent – show sharing of e-
Ionic – show transfer of e-
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Ions minimize potential energy in crystals by forming a crystal lattice.
Distance between all ions represent a balance of attraction between oppositely charged particles and repulsion between like charged particles
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Lattice Energy› Energy released when one mole
of an ionic crystalline compound is formed from gaseous ions
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Ionic High melting
temperature High boiling point Hard Brittle, because
slight shift of crystal can cause it to break
Conduct electricity when dissolved in water
Covalent Low melting
temperature Low boiling point Do not conduct
electricity Not as brittle
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Ionic Formulas Write each ion, cation first. Don’t show
charges in the final formula. Overall charge must equal zero.
› If charges cancel, just write symbols.› If not, use subscripts to balance charges.
Use parentheses to show more than one polyatomic ion.
Stock System - Roman numerals indicate the ion’s charge.
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Ionic Names
Write the names of both ions, cation first.
Change ending of monatomic ions to -ide.
Polyatomic ions have special names.
Stock System - Use Roman numerals to show the ion’s charge if more than one is possible. Overall charge must equal zero.
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Consider the following:› Does it contain a polyatomic ion?
-ide, 2 elements no -ate, -ite, 3+ elements yes
› Does it contain a Roman numeral? Check the table for metals not in Groups 1 or
2.
› No prefixes!
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Common Ion Charges
1+
2+ 3+ NA 3- 2- 1-
0
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potassium chloride
magnesium nitrate
copper(II) chloride
K+ Cl
Mg2+ NO3
Cu2+ Cl
KCl
Mg(NO3)2
CuCl2
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NaBr
Na2CO3
FeCl3
sodium bromide
sodium carbonate
iron(III) chloride
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Lesson Essential Questions:› How is a metallic bond formed?› What are some of the characteristics of a
metallic bond?
Vocabulary: metallic bond, alloy
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Metal ions held together by attraction to free floating electrons. (Sea of electrons)
Good conductors of electricity – Why?
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Malleable Ductile Bond strength – related to enthalpy of
vaporization› The more energy required to vaporize, the
stronger the bond.› See table on page 196.
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A mixture of two or more substances, one of which must be a metal.
Common alloys include steel, 14K gold, 18K gold, cast iron, sterling silver, and bronze.
Within different alloys, there can be different types of mixtures – ex. Steel
Where do we find alloys?
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Use the 3 circle Venn diagram to compare and contrast ionic, metallic, and covalent bonding.
Metallic
Venn Diagram on Chemical Bonding Name______________________________________
Ionic Covalent
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Lesson Essential Questions:› How is the VSEPR Theory useful?› What are the different forces present in
bonding?
Vocabulary:VSEPR theory, hybridization, dipole,
hydrogen bonding, London dispersion forces
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Valence Shell Electron Pair Repulsion Theory
Electron pairs orient themselves in order to minimize repulsive forces.
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Types of e- Pairs› Bonding pairs - form bonds› Lone pairs - nonbonding e-
Lone pairs repel
more strongly than
bonding pairs!!!
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Lone pairs reduce the bond angle between atoms.
Bond Angle
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Draw the Lewis Diagram. Tally up e- pairs on central atom.
› double/triple bonds = ONE pair
Shape is determined by the # of bonding pairs and lone pairs.
Know the 8 common shapes
& their bond angles!
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2 total2 bond0 lone
LINEAR
180°BeH2
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3 total3 bond0 lone
TRIGONAL PLANAR
120°
BF3
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3 total2 bond1 lone
BENT
<120°
SO2
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4 total4 bond0 lone
TETRAHEDRAL
109.5°
CH4
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4 total3 bond1 lone
TRIGONAL PYRAMIDAL
107°
NH3
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4 total2 bond2 lone
BENT
104.5°
H2O
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5 total5 bond0 lone
TRIGONAL
BIPYRAMIDAL120°/90°PCl5
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6 total6 bond0 lone
OCTAHEDRAL
90°
SF6
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PF3
4 total
3 bond
1 loneTRIGONAL
PYRAMIDAL
107°
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CO2
2 total
2 bond
0 loneLINEAR
180°
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Identify the molecular geometry for the following molecules:› HI
› CBr4
› CH2Cl2
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Intermolecular forces = forces between molecules.
› The boiling point of a liquid is a good measure of the intermolecular forces between its molecules: the higher the boiling point, the stronger the forces between the molecules.
Types of intermolecular forces› Dipole-dipole forces› Hydrogen bonding› London dispersion forces
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Dipole – created by equal but opposite charges that are separated by a short distance.
A dipole is represented by an arrow with its head pointing toward the negative pole and a crossed tail at the positive pole. The dipole created by a hydrogen chloride molecule is indicated as follows:
Dipole-dipole forces are the forces of attraction between polar molecules.
H Cl
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The negative region in one polar molecule attracts the positive region in adjacent molecules. So the molecules all attract each other from opposite sides.
Dipole-dipole forces act at short range, only between nearby molecules.
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Hydrogen bonding = intermolecular force in which a hydrogen atom that is bonded to a highly electronegative atom is attracted to an unshared pair of electrons in a nearby molecule.
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London Dispersion Forces = intermolecular attractions resulting from the constant motion of electrons and the creation of instantaneous dipoles.
http://itl.chem.ufl.edu/2045/matter/FG11_005.GIF
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Modern Chemistry Textbook www.nclark.net http://mrsj.exofire.net/chem/ http://cottonchemistry.bizland.com/
chem/chemnotes1.htm http://www.unit5.org/chemistry/