1. Metallic Bonds and the Properties of Metals
Lesson 4
Metallic Bonds and the Properties of Metals

2. Focus Question
How do metals and ionic compounds compare and contrast?

3. New Vocabulary electron sea model delocalized electron metallic bond
alloy

4. Review Vocabulary
physical property: a characteristic of matter that can be observed or measured without altering the sample’s composition

5. Metallic Bonds
In a metallic lattice, the outer energy levels of the metal atoms overlap.
The electron sea model proposes that all metal atoms in a metallic solid contribute their valence electrons to form a “sea” of electrons that surrounds the metal cations in the lattice.

6. Metallic Bonds
The electrons in the outer energy levels of bonding metallic atoms are called delocalized electrons. They can move from one atom to the next.
When an atom’s outer electrons move freely throughout the solid, a metallic cation is formed.
A metallic bond is the attraction of a metallic cation for delocalized electrons.

7. Metallic Bonds The physical properties of metals at the bulk
scale can be explained by metallic bonding.
These properties provide evidence of the strength of metallic bonds.
Examples of physical properties of metals:
— melting and boiling points
— thermal and electrical conductivity
— malleability, ductility, and durability
— hardness and strength

8. Metallic Bonds
In general, metals have moderately high melting points and high boiling points, as shown below.

9. Metallic Bonds
The melting points of metals are less extreme than the boiling points because the cations and electrons are mobile in a metal. It does not take much energy for them to move past each other.
During boiling, atoms must completely separate from the lattice. This requires more energy.

10. Metallic Bonds
The movement of mobile electrons around positive metallic cations makes metals good conductors.
Mobile electrons move heat from one place to another quickly.
Mobile electrons easily move as part of an electric current when an electric potential is applied to a metal.

11. Metallic Bonds Metals are malleable (can be hammered into sheets).
Metals are ductile (can be drawn into wire).
The figure below shows how an applied force causes metal ions to move through delocalized electrons, making metals malleable and ductile.

12. Metallic Bonds
Metals are durable. Metallic cations are strongly attracted to electrons around them and not easily removed from the metal.
As the number of delocalized electrons increases, so does hardness and strength.

13. Metal Alloys
An alloy is a mixture of elements that has metallic properties.
Examples: stainless steel, brass, cast iron
The properties of alloys generally differ from the properties of the elements that they contain.
Example: Steel is iron mixed with at least
one other element. Some properties of iron are present, but steel is stronger than iron.

14. Metal Alloys

15. Metal Alloys Alloys are classified into two basic types.
Substitutional alloy: Some of the atoms in
the original metal are replaced by other metals of similar atomic size.
Example: sterling silver
Interstitial alloy: This alloy is formed when the small holes in a metallic crystal are filled with smaller atoms.
Example: carbon steel

16. Quiz 1. Which of the following is true of the electron sea model?
Metal atoms share their valence electrons with neighboring atoms. A
Metal atoms lose their valence electrons. B
The outer energy levels of the metal atoms overlap. C
CORRECT
None of the above. D

17. Quiz 2.
Identify the name given to the attraction of a metallic cation for delocalized electrons.
ionic bond A
lattice bond C
delocalized bond B
metallic bond D
CORRECT

18. Quiz 3.
What do the physical properties of metals at the bulk scale provide evidence of?
the strength of metallic bonds A
CORRECT
the electron sea model B
delocalized electrons C
the overlapping electron model D

19. Quiz 4. Which of the following is NOT a property of a metal?
durability A
thermal conductivity C
hardness B
low boiling point D
CORRECT

20. Quiz 5. Which of the following is true of alloys?
They have few commercial applications. A
They include salts, oxides, and water. B
Their properties are the same as those of the elements they contain. C
They are mixtures that have metallic properties. D
CORRECT