Ionic Bonds
For review pages 211-227
Sections 8:1- 8:3
Forming Chemical Bonds
The Formation and Nature of Ionic Bonds
Names and Formulas for Ionic Compounds
Valence Electrons
• What are valence electrons
– Valence electrons are the outermost electrons that
are available for bonding
• The number of valence electrons will
determine how many bonds the atom can
form.
• What kind of elements form bonds
– Atoms that have unfilled valence shells are
considered unstable. Atoms will try to fill their
outer shells by bonding with other atoms.
How does an atom become a positive ion?
When an atom loses an electron it becomes a
positive ion called a cation. When a cation
loses outermost valence electron(s):
• Ionic radius is smaller than the atomic
radius.
• Achieves a stable octet like_________
Example:
Sodium (Na) has 11 + and 11 - charges as a
neutral atom. When it loses an electron it has
11 + and 10 - charges or a net charge of +1.
When sodium cations look in the mirror they
see _________.
How does an atom become a negative ion?
When an atom gains an electron it becomes
a negatively charged ion called an anion.
When anions gains an outer most valence
electron:
• Ionic radius is larger than the atomic radius.
• Achieves a stable octet like_________
Example: Chlorine has 17 + and 17 charges. When it gains an electron, it have
17 + and 18 - for a net charge of -1. When
a chloride ion looks in the mirror it sees ___
Atomic vs Ionic Radii
Cations like Lithium get smaller
Anions like Fluoride get bigger
How do ions form neutral compounds?
Positive and negative ions combine their
charges which cancel out to form a neutral
compound.
Example:
Na +1 + Cl -1 becomes NaCl with a zero
net charge
When do ionic bonds form
• Ionic bonds form:
– between metals and non-metals.
– between oppositely charged atoms (ions).
– by the transfer of electrons (exchanging).
• One atom (cation) donates electrons to the
high electronegativity element (anion)
• One atom (anion) take electrons from low
ionization energy elements (cations)
Ionic compounds form crystals
• Ionic bond between ions form crystals
that are regular repeating structures
called lattices.
• In an ionic bond, oppositely charged ions
are strongly held together by electrostatic
forces.
What characteristics do ionic compounds share?
• A crystal structure when solid (lattice)
• A high melting point -many strong bonds to
overcome between the ions
• A high boiling point -many strong bonds to
overcome between the ions
• A tendency to form ions in solution
• Are conductors of electricity in solution or when
melted
• But nonconductors as solids
How does electrical conductivity of ionic compounds
change when they are melted or dissolved in water?
Ionic Compounds tend to
conduct electricity
because their ions
separate in water
allowing for the transfer
of electrons through the
solution.
Electrical conductivity is
the ability of a material
to carry the flow of an
electric current (a flow
of electrons).
How many potassium ions are needed
to balance the charge of one sulfide
ion?
• Potassium has a charge of +1.
• Sulfide has a charge of -2.
• It takes two potassium ions to neutralize
one sulfide ion.
K2S = Potassium sulfide
Predict the formulas for calcium chloride
and potassium phosphate?
Answers
CaCl2
K3PO4
What are polyatomic ions?
+
NH4 ammonium
-3
PO4 phosphate
Because they are composed of two or
more different elements covalently
bonded.
Drawing Ionic Bonds
• We can illustrate ionic bonding using
Lewis structures.
1 – Draw the Lewis structure for each element.
Ex:
Na
Cl
2 – Draw arrows to show the gain/loss of
electrons
Lewis Dot Formula continued
3 – Draw ion Lewis diagrams showing the new
charge for each ion.
Ex:
The chemical formula for the compound formed
represents the ratio of negative ions to
positive ions.
Ex: NaCl – for every 1 sodium ion, there is also 1
chlorine ion.
Practice Drawing Ionic Bonds
Elements
Formula
Calcium
Fluorine
Magnesium
Bromine
Lewis
Ion Lewis
Diagram
Diagram
Where do ions come from?
• Ions can form in a solution.
• Ionic bonds can form between a metal ion
and a nonmetal ion or nonmetallic
polyatomic ion
• Usually from the breaking apart of the ions
of a salt formed by an acid-base reaction
or a metal and acid reaction.
Ionic Compounds Form when
reacting with an acid
• Hydrogen will bond covalently with a
nonmetal such as chlorine to form
hydrochloric acid- HCl.
• A metal will react with an acid to release
hydrogen and form a metallic salt.
Zn + 2 HCl
ZnCl2 + H2
Okay, so is that all?
An acid will also react with a hydroxide
compound of a metallic ion and hydroxide
(OH) ion to form an ionic compound and
water.
3NaOH + H3PO4
Na3PO4 + H2O
Sodium hydroxide and phosphoric acid
become sodium phosphate and water
Okay, so is that all?
A nonmetallic ion such as ammonium can
also form an ionic compound.
NH4OH + HCl
NH4Cl + H2O
ammonium hydroxide and hydrochloric acid
become ammonium chloride and water
Ionic Compound Formulas
The subscript indicates the number of ions of an
element in a molecule of a compound.
Na3PO4
Ca3(PO4)2
3 Na ion and 1 PO4 ion
3 Ca ions and 2 PO4 ions
Note the parens around the polyatomic ion when
a subscript is needed.
Naming Ionic Compounds
The first name of the ionic compound is the
name of the positive ion. The second name
is the name of the negative ion.
positive ion
negative ion
For example:
Magnesium sulfide
Ammonium chloride
Potassium oxide
Vocabulary
•
•
•
•
Ion- a charged atom
Cation- a positively charged ion (lost electron)
Anion- negatively charged ion (gained electron)
Ionic bond- forms when electrons are lost or
gained between ions
• Ions in a crystal are arranged in a lattice.