Notes P.1-2
January 22, 2014
Objectives
• You will be able to:
– Define metallic, ionic, and covalent bonds and
explain their characteristics
– State if two atoms will form a covalent or ionic
bond
– Write ionic formula units
Overview of bonding
• Chemical bond: mutual electrical attraction
between the nuclei and valence electrons of
different atoms that binds those atoms
together.
• Why do atoms bond?
– Most atoms are more stable when they are
bonded than they were as individual atoms
Types of chemical bonds:
• Metallic – sea of electrons
– Occur between: between metals
• Ionic – steal electrons
– Occur between: metal—nonmetal
• Covalent – share electrons
– Occur between: nonmetal—nonmetal
• Covalent or Ionic?
– Determined by electronegativity difference
Remember: Metallic Character
NONMETALS
(IN GREEN)
METALS
(IN YELLOW)
Practice
• Label as ionic, covalent, or metallic:
NaF
CaBr2
H2S
Al2O3
Cu
NO3
•
•
•
•
•
•
Ionic
Ionic
Covalent
Ionic
Metallic
Covalent
METALLIC BONDING
– Results from the attraction of nuclei
to a “sea of electrons”
Sea of Electrons
METALLIC BONDING
– Why an “electron sea”?
• Vacant p and d orbitals in metal's outer
energy levels overlap, and allow outer
electrons to move freely throughout the
metal
– Valence electrons do not belong to any
one atom
METALLIC BONDING
– Common properties of metals:
• High melting/boiling points
• Conduct heat and electricity
• Have luster (shiny)
• Ductile/malleable
– All thanks to the electron sea!
IONIC BONDING
• Results from the electrical attraction between
cations and anions
• Cation: +
• Anion: -
The resulting ions come together due to electrical
attraction (opposites attract)
IONIC BONDING
Common Properties:
• Solid crystals at room temperature
• Very high melting/boiling points
• (Most) Can dissolve in water
• Conduct electricity when melted or
dissolved
Ionic Formula Units
• The net (total) charge on the compound must equal
zero
• Positive and negative cancel out
Hint: Use the criss-cross method
Ionic Formula Units
EXAMPLES:
• Na and Cl
• Na and O
• Ca and O
• Ca and Cl
• Al and O
Ionic Formula Units
EXAMPLES:
• Na and Cl  Na+ + Cl-  NaCl
• Na and O  Na+ + O2-  Na2O
• Ca and O
• Ca and Cl
• Al and O
Na and O
Na2O means that:
Two sodium cations are needed to balance one oxygen anion.
Positive and negative charges must
cancel each other out
EXAMPLES:
• Na+ and Cl• Na+ and O2• Ca2+ and O2• Ca2+ and Cl• Al3+ and O2-
 NaCl
 Na2O
 CaO
 CaCl2
 Al2O3
Total +
Total -
Net
1
2
2
2
6
1
2
2
2
6
0
0
0
0
0
Crystal Lattice
• A network of alternating cations and anions
Ionic compounds
• The formula for ionic
compounds does not
show the exact number
of atoms that are
bonded together.
• The formula tells the
smallest whole number
ratio of atoms that
bond.
COVALENT BONDING
• Results from the sharing of electron pairs
between two atoms (each has a full valence
shell)
• A covalent compound is called a molecule
Each has a full octet
COVALENT BONDING
• Common properties of covalent
compounds:
• Low melting/boiling points
• Many are liquids or gases at room
temp
• Non-conductors of heat and
electricity
Can you…?
– Define metallic, ionic, and covalent bonds and
explain their characteristics?
– State if two atoms will form a covalent or ionic
bond?
– Write ionic formula units?
– Homework 6A, Due Friday
– Lab on Friday