Covalent Bonding

1
Covalent Bonding

• Chapter 8

2
The covalent bond

• Section 8.1

3
The Covalent Bond

• Atoms bond to gain stability and to have access
  to 8 valence electrons (octet rule).
• A covalent bond arises by the sharing of valence
  electrons between nonmetal atoms.
• A molecule is formed when two atoms bond
  covalently.

4
Diatomic Molecules

• Seven elements exist as a pair of atoms, not just
  a single atom. This way they are more stable.
  They are called diatomic molecules.
• You need to memorize these elements
• Nitrogen (N2)
• Oxygen (O2)
• Fluorine (F2)
• Chlorine (Cl2)
• Bromine (Br2)
• Hydrogen (H2)
• Iodine (I2)

5
Single Covalent Bonds

• A single covalent bond occurs when only one pair
  of electrons is shared between atoms.
• The shared electron pair is called a bonding pair
  of electrons.

6
Multiple Covalent Bonds

• Double bonds are formed from the sharing of two
  pairs (4 total) electrons between two atoms.
• Triple bonds are formed from the sharing of three
  pairs (6 total) electrons between two atoms.

7
Naming molecules

• Section 8.2

8
Rules For NamingCovalent (or Binary Molecular)
Compounds

• The first element is named first, using the
  entire element name
• The second element is named, using the root of
  the element name plus the suffix ide.
• Prefixes are used to indicate the number of atoms
  of each element present in the compound.
• Exception THE FIRST ELEMENT NEVER USES THE
  PREFIX MONO!

9
Common Prefixes
10
Examples of NamingCovalent Compounds

• P2O5
• There are 2 phosphorus atoms (shown by the
  subscript)
• There are 5 oxygen atoms (also shown by the
  subscript)
• Name the first element with its prefix
• Diphosphorus
• Name the second element with its prefix and the
  suffix ide
• Pentoxide (not pentaoxide, because of the two
  vowels)
• Put them together ? diphosphorus pentoxide

11
Some Examples

• CCl4
• Carbon tetrachloride (not monocarbon)
• N2O
• Dinitrogen monoxide
• NF3
• Nitrogen trifluoride
• CO
• Carbon monoxide

12
Writing formulas from names

• Use the prefixes to identify the subscripts
• Example carbon dioxide has 1 carbon and 2
  oxygens
• So, it would be written as CO2

13
Some examples

• Triphosphorus Pentachloride
• P3Cl5
• Dinitrogen Trioxide
• N2O3
• Carbon dioxide
• CO2
• Dihydrogen monosulfide
• H2S

14
Molecular structures

• Section 8.3

15
Lewis Structures

• Recall that electron dot structures are used to
  show valence electrons.
• Unpaired electrons in the electron dot structures
  are able to create covalent bonds with other
  atoms.
• In a Lewis structure, they can represent the
  arrangement of electrons in a molecule.

16
Some electron dot structures and single covalent
bonds

• Group 17 have seven valence electrons, so one
  is unpaired these elements can make one single
  covalent bond
• Group 16 have six valence electrons, so two are
  unpaired these elements can make 2 single
  covalent bonds
• Group 15 have five valence electrons, so three
  are unpaired these elements can make 3 single
  covalent bonds.
• Group 14 have four valence electrons, all of
  which are unpaired these elements can make 4
  single covalent bonds

17
Lewis Structures - examples
18
Drawing Lewis Structures

• See page 254 in your book for a summary of the
  steps you might take.
• We will discuss this more in class so you can see
  what is happening.

19
Molecular shapes

• Section 8.4

20
The VSEPR Theory

• Valence Shell Electron Pair Repulsion Theory
• Electron pairs orient themselves in order to
  minimize repulsive forces.

21
Molecular Shapes

• Table on page 263 of your book shows all
  different shapes.
• Go to Glencoe.com for an interactive version
• http//glencoe.mcgraw-hill.com/sites/007874637x/st
  udent_view0/chapter8/concepts_in_motion.html

22
Electronegativity and polarity

• Section 8.5

23
Electronegativity and Polar Bonds

• Electronegativity is an atoms affinity for
  electrons, or its ability to draw electrons to it
• If there is a difference in electronegativity
  between atoms, you will have an unequal sharing
  of electrons, which is called a polar covalent
  bond

24
Electronegativity Differencesand Bond Type
25
Properties of Covalent Compounds

• Weak forces between molecules (called
  intermolecular forces)
• Low melting points
• Low boiling points
• Covalent network solids are formed in some
  substances which lead to very strong solids
  (quartz and diamond are examples)