Metallic Bonding • Observations of the physical properties of metals have led chemists to develop theories to explain these observations.
Physical Properties of Metals • For example, electrical conductivity requires the presence of charged particles that are free to move. • Hardness and high melting points imply strong bonding. • Malleability and ductility suggest that there is regularity in the structure. • From this information, chemists have devised a model to explain and represent the structure and bonding in metal elements.
The Nature of the Metallic Bond • In this model, metal ions, formed when atoms lose their valence electrons, are arranged in a three-dimensional lattice. • This array of ions is surrounded by freely moving electrons that form a “sea” of mobile electrons. • These electrons are said to be delocalized, as they are not confined to a particular location but can move throughout the structure.
The Nature of the Metallic Bond • Electrons are attracted to positively charged ions. • This electrostatic attraction holds the lattice together, and prevents the ions pushing each other apart due to the electrostatic repulsion of like charges. • This type of bonding is called metallic bonding.
The Nature of the Metallic Bond • Why do the metal atoms release their valence electrons to form the sea of electrons? • Metal atoms achieve greater stability by releasing their valence electrons. • Without their valence electrons, the metal atoms achieve a noble gas configuration.
The Nature of the Metallic Bond • When non-metals are present, these valence electrons are transferred to the non-metal atoms, giving rise to the ionic bonding discussed last class. • When only metal atoms are present, the “lost” valence electrons simply become delocalized within the metallic lattice.
Important Properties of Metals • The uses of metals by humans in the past as well as the present centre on two important properties of metals: • Their ability to conduct electricity • Their malleability
Electrical Conductivity • The electrical conductivity can be explained by the presence of the sea of delocalized electrons that surrounds the lattice of positive metal ions. • In the solid state these electrons can move freely and will respond to the application of a potential difference. • When a metal is connected to a power supply, electrons enter one end of the metal and the same number of electrons exits from the other end of the metal.
Malleability • The malleability of a metal is its ability to be beaten or bent into shape without breaking. • Once again the sea of delocalized electrons is responsible for this property of metals. • When a metal is bent, its lattice of positive ions is displaced and there is a possibility of positive ions coming into contact with other positive ions and repelling each other.
Malleability • The constant movement of the delocalized electrons prevents this from occurring, so the metal bends without breaking.