Presentation on theme: "What is metallic bonding?"— Presentation transcript:
1 What is metallic bonding? Metallic bonds are the forces of attraction between free-floating valence electrons and positively charged metal cations.In a metal, cations are packed closely together.The loosely held valence electrons of the metal atoms form a “sea of electrons” that drift freely from one part of the metal to another.The overall charge of the metal is neutral.1. Describe Describe the nature of metallic bonding. Include in your description an explanation of why a metal consists of cations rather than neutral atoms.
2 How does metallic bonding explain metallic properties? Some common properties of metals include:malleability—ability to be hammered or rolled into flat sheets or other shapesductility—ability to be pulled out, or drawn, into wiresthermal conductivity—ability to transfer thermal energy in the form of heatelectrical conductivity—ability to conduct an electric currentEach of these properties may be explained by applying the “sea-of-electrons” model of metallic bonding.(contd.)
3 Malleability When a metal is subjected to pressure, the free-floating valence electrons shield the cations from one another. The cations easily slide past one another, so the metal changes shape rather than breaking apart, as an ionic crystal does.(contd.)
4 Ductility As with malleability, pressure also may be exerted on metals by forcing them through the narrow opening of a die, for example. The metal changes shape but remains as one piece and emerges from the die as a wire.As the wire is forced through the die, the size of the opening in the die determines the diameter of the wire.(contd.)
5 Thermal conductivity Conduction is the transfer of thermal energy with no overall transfer of matter.Conduction occurs within a material or between materials that are touching. Newton’s cradle is a device that helps explain conduction.Newton’s cradle is a model for conduction. When a ball at one end is pulled back and released, energy is transferred from one ball to the next, but only the last ball at the other end moves.In metals, conduction is fast because the mobile valence electrons are free to move. Collisions of electrons transfer thermal energy through the metal.(contd.)
6 Electrical conductivity An electric current is a flow of charged particles. Metals are good conductors of electric currents because the valence electrons can flow freely in the metal. As electrons enter one end of a piece of metal, an equal number of electrons leaves the other end.2. Apply Theories Apply the theory of metallic bonding to explain the metallic properties of malleability and thermal conductivity of aluminum foil.