Covalent%20Bonding

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Covalent Bonding

• Ch 8

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MOLECULAR COMPOUNDS

• 1. Low melting boiling points (sugar)
• 2. Solids, Liquids, and Gases
• 3. Sharing of valence electrons
• 4. Two or more Nonmetallic elements
• that have similar electronegativities
• (also known as covalent bond)
• EX
• H2O CO2

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CHEMICAL FORMULA

• Shows the kinds and number
• of atoms in the
• smallest representative unit
• of the substance.

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• MOLECULAR FORMULA
• 1. Shows the number and kinds of
• atoms present in a molecule of a
• compound (nonmetals only).
• EX
• C2H6 (ethane) CO2 (carbon dioxide)
• H2O (water) CH4 (methane)
• Diatomic molecules
• Heavenly Seven H2, N2, O2, F2, Cl2, Br2, I2
• (Follow pattern on periodic table)

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Molecular Compounds

• Contain Covalent Bonds
• sharing of valence electrons
• between nonmetallic elements.
• Each bond contains two shared electrons

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Covalent Bonding

• 2 or more nonmetals
• Sharing valence electrons
• Valence orbitals overlap
• Want to attain a stable octet
• Bond is a balance of attractive repulsive
  forces
• Simplest case of covalent bonding H2

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Covalent Bonds Dogs of equal
strength.
Covalent bonds can be thought of as two or more
dogs with equal attraction to the bones.  Since
the dogs (atoms) are identical (same
electronegativities), then the dogs share the
pairs of available bones evenly. 
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Lewis Dot Diagrams

• Each dot represents a valence electron
• G.N. Lewis used dots to represent the valence
  electrons in his teaching of chemical bonding. He
  eventually published his theory of chemical
  bonding in 1916.

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Lewis Dot Diagrams
by sharing electrons with other atoms.
Each atom attempts to attain a stable outer
shell electronic configuration
(typically a noble gas electron configuration)
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Structural Formulas
Circle all bonded electron pairs
Lewis dot Diagram

• Bonds are represented with a dashed line

1 single covalent bond (1 shared pair) 3 unshared
pairs
Structural Diagram
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Only the noble gases have exactly the correct
number of electrons to fill their outermost s and
p orbitals.
All other atoms have to lose, gain or share
electrons to attain the stability associated with
the noble gases.
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Types of Bonds

• Single Covalent bond
• Two atoms share one pair of electrons
• X-X
• Double Covalent bond
• Two atoms share two pairs of electrons
• XX
• Triple Covalent bond
• Two atoms share three pairs of electron
• X X

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Types of Bond
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Coordinate Covalent Bonds

• -Formed when one atom contributes both bonding
  electrons in a covalent bond.
• -One atom donates a complete pair of electrons.
• -Up until now, each bonded atom donated one
  electron each

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Coordinate Covalent Bonds

• Now O2 has a stable configuration but carbon
  doesnt

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• So, O2 also donates one of its unshared pairs of
  electrons

Coordinate Covalent Bond is represented with an
arrow
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• Coordinate covalent bond is shown with arrows

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Resonance

• Occurs when two or more valid electron dot
  formulas can be written for a molecule.
• EX O3 ozone
• Electron pairs shifted without changing the
  position of the oxygen atoms.
• More than 1 electron dot structure can be drawn

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Resonance (continued)

• Occurs when two or more valid electron dot
  formulas can be written for a molecule.
• EX O2 Oxygen
• Octet rule not satisfied (8 valence electrons)
  but Oxygen can exist with only a single covalent
  bond.
• More than 1 electron dot structure can be drawn

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How to Name a Molecular Formula

• Ex CO CO2
• 1. Element with the () apparent charge comes 1st
• carbon carbon
• 2. Second element ends in IDE
• carbon oxide carbon oxide
• 3. Use prefixes to distinguish between compounds
  to show how many atoms of each element are
  present
• carbon monoxide carbon dioxide

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Prefixes for Molecular Compounds
1 mono Dont use for first named element
2 di Ex CO
3 tri carbon monoxide
4 tetra
5 penta
6 hexa
7 hepta
8 octa
9 nona
10 deca

• 1. drop vowel on prefix if element starts with
  vowel
• EX monooxide
• monoxide
• 2. Dont drop vowel for
• di and tri prefixes

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• EXAMPLES

NO
NO2
N2O
N2O3
PCl5
CS2
SF6
nitrogen monoxide
nitrogen dioxide
dinitrogen monoxide
dinitrogen trioxide
phosphorus pentachloride
carbon disulfide
sulfur hexafluoride
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How to Write a Molecular Formula

1. Write down element symbol
2. Prefixes give you what subscripts to use

• Ex
• Carbon tetrachloride
• Sulfur trioxide
• Tetraiodine nonoxide

Ex Carbon tetrachloride Sulfur trioxide
Tetraiodine nonoxide
Ex Carbon tetrachloride Sulfur trioxide
Tetraiodine nonoxide
Ex Carbon tetrachloride Sulfur trioxide
Tetraiodine nonoxide
CCl
CCl4
SO
SO3
I O
I4O9
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3D

• Electron dot structures and structural formulas
  only show 2D
• In Reality
• Molecules are not flat structures
• They are 3-dimensional shapes

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VSEPR THEORY

• Valence-shell Electron-pair Repulsion Model
• Valence electron pairs repel molecules adjust
  their shapes so that the electron pairs are as
  far apart from one another as possible
• Unshared pairs repel shared pairs
• more strongly

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Unshared pair repel shared pair strongly
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SHAPES OF MOLECULES
Bond Angle Molecular Geometry Formula Picture
180o Linear CO2
109.5o Tetrahedral CH4
107o Pyramidal NH3
105o Bent H2O