Chemistry – Chapter 6.4

1. Chemistry – Chapter 6.4 Metallic Bonding

2. Objectives • Describe the electron-sea model of metallic bonding, and explain why metals are good electrical conductors. • Explain why metal surfaces are shiny. • Explain why metals are malleable and ductile but ionic-crystalline compounds are not.

3. Metallic Bonding • Chemical bonding is different in metals than it is in ionic, molecular, or covalent-network compounds. • Difference is reflected in the unique properties of metals. • They are excellent electrical conductors in the solid state. • Property is due to the highly mobile valence electrons of the atoms that make up a metal. • In metals, the valence electrons are shared by all surrounding atoms.

4. Delocalization • Within a metal, the vacant orbitals in the atoms’ outer energy levels overlap. • The overlapping of orbitals allows the outer electrons of the atoms to roam freely through the entire metal. • The electrons are delocalized, which means they do not belong to any one atom but move freely about the metal’s network of empty atomic orbitals.

5. Mobile Electrons • These mobile electrons form a sea of electrons around the metal atoms, which are packed together in a crystal lattice. • Metallic Bonding: The chemical bonding that results from the attraction between metal atoms and the surrounding sea of electrons. • Mobile electrons in the metallic bond are responsible for luster, thermal conductivity, and electrical conductivity.

6. Metallic Properties • The freedom of electrons to move in a network of metal atoms accounts for the high electrical and thermal conductivity characteristic of all metals. • Because they contain many orbitals separated by extremely small energy differences, metals can absorb a wide range of light frequencies. • Absorption results in the excitation of the metal atoms’ electrons to higher energy levels. • The electrons immediately fall back down to lower levels, emitting energy in the form of light. • De-excitation is responsible for their shiny appearance. • The metals basically absorb then re-emit the light.

7. Malleability and Ductility • Most metals are also easy to form into desired shapes. • Malleability: the ability of a substance to be hammered or beaten into thin sheets. • Ductility: The ability of a substance to be drawn, pulled, or extruded through a small opening to produce a wire, without breaking. • The malleability and ductility of metals are possible because metallic bonding is the same in all directions throughout the solid. • In other words, the fact that metals are malleable and ionic crystals are brittle is explained in terms of their chemical bonds.

8. Metallic Bond Strength • Metallic bond strength varies with the nuclear charge of the metal atoms and the number of electrons in the metal’s electron sea. • Both of these factors are reflected in a metal’s heat of vaporization. • When a metal is vaporized, the bonded atoms in the normal (usually solid) state are converted to individual metal atoms in the gaseous state. • The amount of heat needed to vaporize the metal is a measure of the vapor strength of the bonds that hold the metal together. • In general, the strength of the metallic bond increases moving from left to right on any row of the periodic table.