Unit 1 – Day 3
Bonding
The Stable Octet
• Atoms are most stable when they have a full
outer shell of electrons. This is why noble
gases, which have a full shell, do not react.
• For other elements, they will need to gain or
lose electrons to obtain a full outer shell.
Ions
• When an atom gains or loses electrons, it
becomes a charged ion.
• If an atom loses negative electrons, it
becomes positive.
• If an atom gains negative electrons, it
becomes negative.
• Example:
Na  Na+ + eS + 2e-  S2-
Metals
• Metals are elements on the left side of the
periodic table, like sodium or iron.
• They have less than 4 electrons in their outer
shell.
• They tend to lose electrons and become
positive ions.
Non-metals
• Non-metals are elements on the right side of
the periodic table, like oxygen or chlorine.
• They have more than 4 electrons in their outer
shell.
• They tend to gain electrons and become
negative ions.
Ionic Bonds
• Metals tend to give their electrons to nonmetals, so they can both get a full outer shell.
• The metal and non-metal ions are opposite
charges, and they attract.
• This attraction is called an ionic bond.
Properties of Ionic Compounds
• An ionic bond is very strong.
• As well, the ions arrange themselves so that
molecules attract to other molecules nearby.
Properties of Ionic Compounds
• Because of this, it is very difficult to pull apart
ionic molecules.
• This affects many properties.
• Melting Point:
– Ionic compounds are very difficult to melt,
because in order to make a liquid, molecules need
to move farther apart.
Properties of Ionic Compounds
• Smell
– Ionic compounds have no smell, because in order
to enter the air, molecules would need to leave
the surface.
• Hardness
– Ionic compounds are hard to crush, because the
network of molecules supports each other in a
crystal.
Properties of Ionic Compounds
• Solubility
– Ionic compounds
dissolve in
substances like
water. The charges
from a water
molecule pull apart
the ions.
Properties of Ionic Compounds
• Electrical Conductivity
– When melted or dissolved, ionic compounds
separate into ions. These ions can carry electrical
charges.
Covalent Bonds
• Non-metals need to gain electrons to fill their
outer shell, so they sometimes share electrons
with each other.
• When two non-metals share electrons, it is
called a covalent bond.
Pure Covalent Bonds
• If the atoms are the same, they share equally.
This is called a pure covalent bond.
• Ex: H2, O2, N2 , CH bonds
• Pure covalent compounds have no charges, so
the molecules don’t attract each other as well
as ionic compounds do.
Pure Covalent Properties
• Pure covalent compounds have the following
properties:
– Strong odour (molecules escape into the air easily)
– Crush easily (no crystal support)
– Do not dissolve in water (no charges to attract)
– Do not conduct electricity (no ions)
– Low melting pt. (molecules are easy to separate)
Polar Covalent Compounds
• Sometimes when atoms share electrons, the
electrons are closer to one atom than the
other.
• This results in one atom having a slight
negative charge, and the other having a slight
positive charge.
Polar Covalent Properties
• Pure covalent compounds have the following
properties:
– No odour (slight charge holds molecules in place)
– Hard (charges have some crystal support)
– Dissolve in water (slight charges attract water)
– Do not conduct electricity (no ions)
– Average melting point (molecules are easier to
separate than ionic, but not as easy as pure cov.)
Table of Properties
• Use your notes to summarize into a table the
properties of the three types of compounds.