Chapter : Chemical Bonding

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Chapter Chemical Bonding
Cartoon courtesy of NearingZero.net
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Chemical Bonds Lect1

• Forces that hold groups of atoms together and
  make them function as a unit.
• Ionic bonds transfer of electrons Metal
  Nonmetal Ex) NaCl Li2O
• Covalent bonds sharing of electrons. 2
  nonmetals Ex) CH4 CO2
• Metallic bonds- electrons are free to move
  throughout the material. Metals

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Covalent Bonding

• Molecule- is the smallest unit quanitity of
  matter which can exist by itself and retain all
  the properties of the original substance.
• When a compound is formed by sharing electrons,
  the compound is called a
• ____Molecule__________________
• Examples H2O O2
• Diatomic molecule- is a molecule containing 2
  identical atoms. (H2 N2 O2 F2 Cl2 Br2 I2)
• H NO F

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Covalent Bonding

• Diatomic molecule- is a molecule containing 2
  identical atoms.
• (H2 N2 O2 F2 Cl2 Br2 I2)
• H NO F

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Naming Covalent Compounds

• Two words, with prefixes
• Prefixes tell you how many.
• 1-mono, 6- hexa
• 2-di, 7- hepta (greek)
• septa
  (latin)
• 3-tri, 8-octa
• 4-tetra, 9-nona
• 5-penta, 10- deca

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Naming Covalent Compounds

• First element whole name with the appropriate
  prefix, except mono
• Second element, -ide ending with appropriate
  prefix
• Practice

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Naming Covalent Compounds

• CO2
• CO
• CCl4
• N2O4
• XeF6
• P2O9
• H2O

• Carbon Dioxide
• Carbon Monoxide
• Carbon tetrachloride
• Dinitrogen tetroxide
• Xenon hexaflouride
• Diphosphorus Nonaoxide
• Dihydrogen Monoxide
• Water!

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Covalent compounds

• The name tells you how to write the formula
• duh
• Sulfur dioxide SO2
• diflourine monoxide F2O
• nitrogen trichloride NCl3
• diphosphorus pentoxide P2O5

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Empirical formula

• Shows the lowest, simplified ratio of elements in
  a compound

Molecule Molecular formula Empirical formula
1 C2H4 CH2
2 C4H8 CH2
3 C3H8 ?
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• Chemical Formula- represents the relative of
  atoms of each kind in a chemical compound by
  using atomic symbols and numerical subscripts.
  Example H2O H2 O1
• Molecular compound (Covalent Compounds) -
  simplest formula unit are molecules. Have low
  melting boiling pts.
• Molecular formula- shows the types and numbers of
  atoms combined in a single molecule.

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• Bond Length- is the average distance between 2
  bonded atoms.
• Bond Energy- is the energy required to break a
  bond.
• It gives us information about the strength of a
  bonding interaction.

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I. Lewis Diagrams(p. 202 213)

• Lecture 2

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The Octet Rule

• Chemical compounds tend to form so that each
  atom, by gaining, losing, or sharing electrons,
  has an (8) octet of electrons in its valence
  shell.

8 is Great!
H
He
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Lewis Dot

• Shows how valence electrons are arranged among
  atoms in a molecule.
• Reflects central idea that stability of a
  compound relates to noble gas electron
  configuration.

CH4
H2O
I started it for you
Try one yourself NH3
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A. Octet Rule

• Remember
• Most atoms form bonds in order to have 8 valence
  electrons.

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B. Drawing Lewis Diagrams

• Find total of valence e-.
• Arrange atoms - singular atom is usually in the
  middle.
• Form bonds between atoms (2 e-).
• Distribute remaining e- to give each atom an
  octet (recall exceptions).
• If there arent enough e- to go around, form
  double or triple bonds.

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B. Drawing Lewis Diagrams

• CF4

1 C 4e- 4e- 4 F 7e- 28e- 32e-
F F C F F
- 8e- 24e-
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B. Drawing Lewis Diagrams

• CO2

1 C 4e- 4e- 2 O 6e- 12e- 16e-
O C O
- 4e- 12e-
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B. Drawing Lewis Diagrams

• BeCl2

1 Be 2e- 2e- 2 Cl 7e- 14e- 16e-
Cl Be Cl
- 4e- 12e-
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A. Octet Rule

• Exceptions

• Hydrogen ? 2 valence e-

• Groups 1,2,3 get 2,4,6 valence e-

• Expanded octet ? more than 8 valence e- (e.g. S,
  P, Xe)

• Radicals ? odd of valence e-

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C. Polyatomic Ions

• To find total of valence e-
• Add 1e- for each negative charge.
• Subtract 1e- for each positive charge.
• Place brackets around the ion and label the
  charge.

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C. Polyatomic Ions

• ClO4-

1 Cl 7e- 7e- 4 O 6e- 24e- 31e-
O O Cl O O
1e- 32e-
- 8e- 24e-
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C. Polyatomic Ions

• NH4

1 N 5e- 5e- 4 H 1e- 4e- 9e-
H H N H H
- 1e- 8e-
- 8e- 0e-
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Electornegativity

• Lecture 3

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Is it Covalent or ionic

• Nonpolar-Covalent bonds (H2)
• Electrons are equally shared
• Electronegativity difference of 0 to 0.5
• Polar-Covalent bonds (HCl)
• Electrons are unequally shared
• Electronegativity difference between .5 and 2.1
• 3. Ionic Bonds 2.1- 3.3

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Using Electronegativity differences

• CO 3.5-2.5 1.0 polar
  covalent
• C2.5 look on table pg 198
• O 3.5 2.1 thru 3.3 Ionic Bond

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Electronegativity

• 
  

Nonpolar Covalent Polar covalent
Ionic
0-------------?0.5 -------------------------------
-------- gt2.1 ---------?3.3
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practice

• NaCl Na0.9 Cl3.2 3.2-0.92.3
• NaCl is ionic
• CO 3.4- 2.6 0.8 Polar covalent
• CH4 2.6 -2.2 0.4
  Non polar covalent

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D. Resonance Structures

• Molecules that cant be correctly represented by
  a single Lewis diagram.
• Actual structure is an average of all the
  possibilities.
• Show possible structures separated by a
  double-headed arrow.

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D. Resonance Structures

• SO3

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• D. Resonance-Occurs when more than one valid
  Lewis structure can be written for a particular
  molecule.

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Structural Formula

• Shows shared pair of electrons by a dashed line.

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• Single bond- 1 pair of electrons
• Double bond- 2 pair of electrons
• Triple bond- 3 pair of electrons
• Try a couple
• O2
• N2

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Ionic Bonding and Compounds

• Ionic Compound- is composed of positive and
  negative ions combined so that the positive
  negative charges are equal. (Metal nonmetal)
• Formula Unit- is the simplest collection of atoms
  from which a compounds formula can be established.

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Writing Formulas

• Write the symbols of each element
• Put their charge in their upper right corner
• Crisscross the numbers down (Not the charges).
• Example
• Write the formula for Magnesium Chloride
• Mg Cl
• Mg2 Cl-1
• Mg2 Cl-1
• MgCl2

MgCl2
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Writing Formulas Practice
1
2
3 4 -3 -2
-1

• Write the formula for
• Aluminum Bromide
• Calcium Oxide
• Calcium Nitride
• Sodium Chloride

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• Lattice Energy- is the energy released when 1
  mole of an ionic crystalline compound is formed
  from gaseous ions.
• Ionic Compounds have high melting points
  boiling points, are hard and brittle, have
  crystalline structure.

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Polyatomic Ions

• Many atoms with a charge.
• Example SO4-2

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Metallic Bonding

• Metals- conduct heat, have low ionization energy
  electronegativity, give up e-
• Metallic Bond- is a chemical bond resulting from
  the attraction between positive ions and
  surrounding mobile e-.
• Malleability and ductility

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Molecular Geometry

• VSEPR Theory- Valence- shell, electron-pair
  repulsion
• states that repulsion between the sets of
  valence-level electrons surrounding an atom cause
  these sets to be oriented as far apart as
  possible.

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Determining VSEPR

• Determine the VSEPR for H2O
• Draw the Lewis Dot
• Draw the Structural Formula
• Label the central atom as A
• Label any atoms attached to the center atom as B
• Label any paired electrons on the central atom
  that are not used in the bond as E

H-O-H
E2
B
B
A
VSEPR AB2E2 Shape Bent (look on chart)
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VSEPR Chart
VSEPR SHAPE
AB or AB2 Linear
AB2E Bent
AB3 Trigonal-Planar
AB4 Tetrahedral
AB3E Trigonal-Pyramidal
AB2E2 Bent
AB5 Trigonal-Bipyramidal
AB6 Octahedral
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• Hybridization-The Blending of Orbitals.
• Dipole- is created by equal but opposite charges
  that are separated by a short distance.
• Dipole-Dipole Attractions-Attraction between
  oppositely charged regions of neighboring
  molecules.
• Hydrogen Bonding- Bonding between hydrogen and
  more electronegative neighboring atoms such as
  oxygen and nitrogen. Hydrogen bonding in Kevlar,
  a strong polymer used in bullet-proof vests.
• London Dispersion Forces- The temporary
  separations of charge that lead to the London
  force attractions are what attract one nonpolar
  molecule to its neighbors. London forces increase
  with the size of the molecules.

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• Electronegativity chart. Table. Aug. 9, 2006.
  http//www.chemistry210.com/notes/u01s06f.htm
• Lewis Structures. Drawings. Aug. 9, 2006.
  http//www.avon-chemistry.com/chem_bond_explain.ht
  ml
• Oscar. Photo. Aug. 9, 2006. http//www.musicmerc
  hant.com/22061.htm
• Water Structural Formula. Drawing. Aug. 10,
  2006. http//www.accs.net/users/kriel/ch4notes/wat
  er_structural_formula.gif
• Periodic Table of Elements. Chart. Aug. 9,
  2006. http//users.erols.com/kdennis/periodictable
  .jpg
• Information. Aug 11, 2006. http//www.sciencegee
  k.net/Chemistry/Powerpoint/Unit3/Unit3_files/frame
  .htm
• Holt, Rinehart and Winston. Modern Chemistry.
  Harcourt Brace Company. 1999.