Ionic Bonds
Objective/Warm-Up
• SWBAT describe ionic bonds and
write ionic formulas.
• Which element has more
electronegativity?
• Na Cl
• Ca O
• Cs F
Valence electrons
– An atom’s outermost electrons
Valence shell
– Outer shell which valence electrons occupy
Lewis dot structure (electron dot configuration)
– Shows valence electrons as a series of dots
surrounding an atomic symbol
– Place one dot around at a time before you
double up
– Maximum of 8 dots (4 pairs of 2)
Paired valence electrons
–
–
–
–
Relatively stable
Resistant to change
Don’t form chemical bonds
Called non-bonding pairs
Unpaired valence electrons
– Have a strong tendency to participate in
chemical bonding
Atoms tend to form chemical bonds so that they
each have 8 electrons (in pairs) in their
valence shells (octet rule)
– This is similar to electron configuration of a
noble gas
The Octet Rule
• The octet rule says:
– Atoms tend to gain or lose electrons in order
eight
to have _________
valence electrons.
• For example:
– How many valence electrons does
CHLORINE have?
– How many more does it need to have 8?
– What would happen if chlorine gained an
eighth valence electron?
Ions and Lewis Dot
Structures
• Find the number of valence electrons
• Following the octet rule, find how
many electrons will be gained or lost
for each atom to become an ion.
• Combine the ions to form compounds.
Practice
• Combine the following atoms to form
ionic compounds (show Lewis dot
structures).
• Na Cl
• Mg F2
• Na2 O
Electrons occupy innermost shell first
– Exposed electrons in outer shell responsible
for bonding
Chemical bond
– Force of attraction between atoms that holds
them together
A. Ion
•
An atom having a positive or negative
charge
B. Cation
– An ion where electrons are lost
– Has a positive charge
– Na1+ → Na+
1. Electron dots for cations
– Metals will have few valence
electrons
Ca
1. Electron dots for cations
– Metals will have few valence
electrons
– These will come off
Ca
1. Electron dots for cations
– Metals will have few valence
electrons
– These will come off
– Forming positive ions
2+
Ca
C. Anion
– An ion where electrons are gained
– Ion has an overall negative charge
– Cl1- → Cl-
1. Electron dots for anions
– Non-metals will have many valence
electrons
– They will gain electrons to fill outer
shell
P
P
1. Electron dots for anions
– Non-metals will have many valence
electrons
– They will gain electrons to fill outer
shell
– Forming negative ions
3P
D. Ionization Energy
– The amount of energy needed to
remove an electron from an atom
– The closer the electron is to the
nucleus, the harder it is to remove
E. Ionic bond
• Transfer of electrons
• Formation of cations and anions
Na + Cl
+
Na
+
Cl
E.
•
•
•
Ionic bond
Transfer of electrons
Formation of cations and anions
Opposite charges hold ions together
NaCl
F. Ionic compounds
1. Are highly ordered compounds
•
•
•
each anion actually attracts several
cations
These attract several more anions
A network of ions forms crystals
F. Ionic compounds
2. Consist of elements found on
opposite sides of the periodic table
3. Positive and negative charges must
balance (Oxidation numbers)
4. When melted or dissolved, they
carry an electrical charge
Criss-cross method
•
•
•
•
•
•
Examples:
Mg
Cl
Na
S
Al
Br
Ca
N
Ba
P
•
•
•
•
K S
Sr F
Cs P
Al O
Essential QuestionsCh.7-Bonding
• How do I distinguish between ionic,
covalent, and metallic compounds?
• How are ionic and covalent
compounds named?
• How do I write the formula for ionic
and covalent compounds?
Objective/Warm-Up
• SWBAT write formulas for ionic
compounds.
• What charges do the following
elements have when they form ions?
•
•
•
•
•
F
Ca
K
N
O
Monatomic vs.
Polyatomic Ions
Practice
Objective/Warm-Up
• SWBAT write formulas for ionic
compounds.
• What is an ionic bond?
• List at least 3 characteristics of an
ionic bond.