7.1 Ions
• Ions are atoms that have gained or lost
electrons….
• Have a net electrical charge
• Cations
• Anions
• Valence electrons are gained or lost
What are valence electrons?
• Electrons in the highest energy level of an
atom
• Elements within a group have the same
number of valence electrons
• Number of valence electrons largely
determines properties of the element and
its group
• Number of ve’s indicated by the group A
group numbers, IA, IIA, IIIA, etc.
Valence Electrons
1s1
1s22s22p2
1s22s22p3
1s22s22p4
Electron Dot Structures
Valence electrons represented as dots
What is the octet rule?
• Noble gases are extremely unreactive, i.e.
very stable
• When forming ions or compounds,
representative elements (Group A) gain,
lose, or share electrons in order to achieve
a noble gas electron configuration
• i.e. an octet, ns2np6
Metals vs. Nonmetals
• Metals tend to give up ve’s to achieve an
octet
• Nonmetals tend to gain or share ve’s to
achieve an octet
Formation of Cations
• When Na loses its valence electron, there is an
octet in the next lowest energy level
Formation of Cations
•The electron configuration of the sodium ion is the
same as that of a neon atom.
Transition Metals
• Do not follow the octet rule
• “Pseudo-noble gas” configuration
Formation of Anions
• Non-metals tend to gain ve’s to achieve an
octet (noble gas e- configuration)
Formation of Anions
Formation of Anions
•Both a chloride ion and the argon atom have an octet
of electrons in their highest occupied energy levels.
How can you predict the charge
of a monatomic ion?
• Determine number
of ve’s
• Representative
elements will gain
or lose the least
number of ve’s to
achieve an octet
Common Anions:
Monatomic and Polyatomic
7.2 Ionic Compoounds
• Usually composed of
a metal and non-metal
Ionic Bonds & Ionic Compounds
• Ionic Compounds
– Composed of ions
• Cations and anions
– Held together by ionic bonds
– Are electrically neutral
Ionic Bonds
• Ionic Bonds are….
– electrostatic forces of attraction between oppositely
charged ions
Formula Unit
• Chemical formula for an ionic compound
• Lowest whole number ratio of ions in the
compound producing an electrical
neutrality
• What is the formula unit for…
Sodium chloride
Magnesium chloride
Sodium sulfide
Magnesium oxide
What are the properties of
ionic compounds?
•
•
•
•
•
Solids
High melting points
3D arrangement of ions
Coordination number
Conduct electric current when dissolved in
water
Crystalline Solids:
Specific 3D Arrangement of Ions
“crystal lattice”
Coordination Number
• Number of ions
surrounding an
oppositely charged
ion
High melting temperatures (mp)
• Because ionic bonds are very strong, it
takes much energy to break them
• Therefore, their mp’s are high
Sample mp’s of ionic compounds
Compound
Name
Formula Unit
mp (ºC)
NaCl
801
MgO
2852
LiF
845
Sr(NO3)2
570
KNO3
334
Conduct electricity if molten or
dissolved in water (aqueous)
Electrical
current is a
movement of
charge
Because ions
are free to
move in the
molten or
aqueous
state
Structure of Metals
“Electron sea” model of
metals
valence electrons are free to
move about in metals
Metallic bonds: attraction
between valence electrons
and the metal cations
Properties of Metals are due to the
Structure of Metals
•
•
•
•
•
Ductility
Malleability
Electrical conductivity
Luster
Thermal conductivity
Compare Properties of Metals and
Ionic Compounds
Property
Metals
Ionic
Compounds
Malleability &
ductility
High
Brittle
Electrical
conductivity as solid
High
None
Luster
High
Low or none
Thermal
conductivity
High
Low or none
Compare Structure of Metals &
Ionic Compounds
Crystal Structure of Metals
• Metal atoms arranged in orderly, compact
patterns
• Unit Cell & Crystal Lattice
Alloys
• Mixtures of which at least one component
is a metal
• Have superior properties to the pure
metal,
– hardness, tensile strength, durability,etc.
Some bicycle frames are often made
of titanium alloys that contain
aluminum and vanadium.
Steel
There are many alloys of
steel used for different
applications
Vocational & Professional
Opportunities…
Metallurgy & metallurgical
engineering
Welding & welding
engineering