Introduction to Chemical Bonding

1
Introduction to Chemical Bonding

• Bond Formation
• Ionic Bonds
• Covalent Bonds

2
Chemical Bonds

• An attractive force that holds atoms together
• Formation of chemical bonds involves energy
• Bonds will form if atoms have lower energy than
  when they are separated
• Bond formation is (generally) an exothermic
  process
• Bonding deals with valence electrons
• Electrons in the highest energy level

3
Lewis Structures

• Symbolic representations of elements that show
  the valence electrons
• Elemental symbol and the valence electrons
  represented by dots

4
Valence Electrons Noble Gases

• Noble gases are unreactive
• They dont form compounds with other elements
• Noble Gases already have a stable electron
  configuration
• The highest energy level of the atom is full and
  it will not form any bonds
• Does this always mean there are eight electrons?
• No ? Helium

5
Valance Electrons and Chemical Properties

• The number of valence electrons determines the
  chemical properties of an atom
• Atoms are trying to get to eight valance
  electrons and they will take the shortest route
  to get there
• Octet Rule
• Could mean gaining electrons, could mean loosing
  electrons
• 1,2,3,4,5,6,7,8,1,2,3,4

6
Ion Formation and the Octet Rule

• Octet Rule
• Atoms will gain or lose electrons to have a full
  outer shell (valence shell)
• Metals lose valence electrons so that the
  electron configuration becomes like the previous
  noble gas
• Non-metals gain electrons to become like the next
  noble gas
• Exceptions exist for small atoms
• Duet Rule

7
How does the bond between sodium chlorine form?
Sodium has one valence electron. Its looking to
lose it
Na
?
Chlorine has seven valence electrons. Its
looking to gain one
8
Ion Formation and the Octet Rule

• Main group metals lose all their valence
  electrons to form cations
• This loss of electrons is called oxidation
• Non-metals gain electrons to achieve the noble
  gas configuration and form anions
• This gain of electrons is called reduction
• OiL RiG
• Oxidation is loss, Reduction is gain

9
How does the bond between sodium chlorine form?
Chlorine now has 17 protons 18 electrons. It
has a negative charge. It is an anion
Sodium now has 11 protons 10 electrons. It has
a positive charge. It is a cation
Na
10
Ionic Bond

• Negative charges are attracted to positive
  charges
• Negative anions are attracted to positive cations
• The result is an ionic bond
• Ionic Bonds involve the transfer of electrons
  from a metal to a non-metal

11
How does the bond between sodium chlorine form?
Na
The negative charge on the chloride ion and the
positive charge on sodium ion attract each other
and form an ionic bond
12
Structure of an Ionic Solid

• Ionic Compounds form a three-dimensional network
  called a crystal (or crystal lattice)
• Each ion is attracted to multiple ions of the
  opposite charge

13
Properties of Ionic Compounds

• High melting point
• Dont easily change to liquids (or gases)
• Solids ? Poor conductors
• Liquids ? Good Conductors
• Shatters when breaks