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Covalent%20Bonding

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Title: Covalent%20Bonding


1
Covalent Bonding
  • Ch 8

2
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

3
CHEMICAL FORMULA
  • Shows the kinds and number
  • of atoms in the
  • smallest representative unit
  • of the substance.

4
  • 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)

5
Molecular Compounds
  • Contain Covalent Bonds
  • sharing of valence electrons
  • between nonmetallic elements.
  • Each bond contains two shared electrons

6
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

7
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. 
8
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9
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.

10
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)
11
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
12
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.
13
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

14
Types of Bond
15
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

16
Coordinate Covalent Bonds
  • Now O2 has a stable configuration but carbon
    doesnt

17
  • So, O2 also donates one of its unshared pairs of
    electrons

Coordinate Covalent Bond is represented with an
arrow
18
  • Coordinate covalent bond is shown with arrows

19
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

20
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

21
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

22
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

23
  • EXAMPLES

NO
NO2
N2O
N2O3
PCl5
CS2
SF6
nitrogen monoxide
nitrogen dioxide
dinitrogen monoxide
dinitrogen trioxide
phosphorus pentachloride
carbon disulfide
sulfur hexafluoride
24
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
25
3D
  • Electron dot structures and structural formulas
    only show 2D
  • In Reality
  • Molecules are not flat structures
  • They are 3-dimensional shapes

26

27
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

28
Unshared pair repel shared pair strongly
29
SHAPES OF MOLECULES
Bond Angle Molecular Geometry Formula Picture
180o Linear CO2
109.5o Tetrahedral CH4
107o Pyramidal NH3
105o Bent H2O
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