Download Ionic and Covalent Bonding

Ionic and Covalent Bonding
REVIEW valence electrons:
• the electrons in the highest occupied energy level of
an element’s atom
• the number of valence electrons determines the
chemical properties of an element
• usually the only electrons used in bonds
• how to determine # of valence electrons?
1. look at electron configuration
2. trend on periodic table (group# = #valence electrons)
Ionic and Covalent Bonding
Lewis Dot Structures:
• diagrams that show the valence electrons as dots
The Octet Rule:
• An octet is a set of 8
• In forming compounds, atoms tend to achieve the
electron configuration of a noble gas (8 valence
electrons)
• Exceptions: Boron (wants 6 v.e.’s) and Phosphorous,
which uses vacant d orbitals to form extra bonds.
Ionic Bonding (metal + nonmetal)
• Metals tend to lose their valence electrons, leaving a
complete octet in the next-lowest energy level, to form
cations.
• Nonmetals tend to gain electrons or share electrons
with another nonmetal to achieve a complete octet to
form anions.
Ionic Bonds
Anions and cations have opposite charges
and attract on another by electrostatic
forces.
Ionic Bonds bind oppositely charged ions.
The total positive charges of cations =’s the
total negative charges or the anions ... so,
compounds are neutral.
Properties of Ionic Bonds
Crystalline solids at room temperature
Ions are arranged in repeating threedimensional patterns.
In these patterns, each ion is strongly attracted
to its neighbors and the structure is very stable
--> ionic compounds have a high melting point.
When melted, ionic compounds can conduct
electricity.
Metallic Bonding (metal + metal)
• Metals are like ionic compounds in some ways.
• Metallic Bonds consist of + metal ions packed
together, surrounded by a “sea” of valence electrons.
• These valence electrons can travel from one end of a
piece of metal to the other --> excellent electrical
conductors.
• Metals = simplest crystalline solids.
• Alloys: mixtures made of two or more elements, at
least one is a metal. Ex: Brass= Cu + Zn
Covalent Bonding (nonmetal + nonmetal)
• Atoms form covalent bonds when they share
electrons to form an octet.
• 1 shared PAIR (2 electrons) = a single bond
• 2 shared PAIRS (4 electrons) = a double bond
• 3 shared PAIRS (6 electrons) = a triple bond
• RESONANCE STRUCTURES: more than one electron dot
structure can be drawn.