Section 6-4: Metallic Bonding Coach Kelsoe Chemistry Pages

Section 6-4 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.

Metallic Bonding Chemical bonding is different in metals than it is in ionic, molecular, or covalent- network compounds. Metals are excellent electrical conductors in the solid state, due to the highly mobile valence electrons of the atoms that make them up.

The Metallic-Bond Model The highest energy levels of most metal atoms are occupied by very few electrons. Many of the atoms have unoccupied p and d orbitals. Within a metal, the vacant orbitals in the atoms’ outer energy levels overlap.

The Metallic-Bond Model This overlapping of orbitals allows the outer electrons of the atoms to roam freely throughout the entire metal. The electrons are delocalized, which means that they do not belong to any one atom but move freely about the metal’s network of empty atomic orbitals.

The Metallic-Bond Model These mobile electrons form a sea of electrons around the metal atoms, which are packed together in a crystal lattice. The chemical bonding that results from the attraction between metal atoms and the surrounding sea of electrons is called metallic bonding.

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. Metals can also absorb a wide range of light frequencies. This absorption of light 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. This gives metals their shiny appearance.

Metallic Properties Most metals are also easy to form into desired shapes. Malleability is the ability of a substance to be hammered or beaten into thin sheets. Ductility is the ability of a substance to be drawn, pulled, or extruded through a small opening to produce a wire.

Metallic Properties The malleability and ductility of metals are possible because metallic bonding is the same in all directions throughout the solid. One plane of atoms in a metal can slide past another without encountering any resistance or breaking any bonds.

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. These factors are reflected in a metal’s heat of vaporization. The higher the heat of vaporization, the stronger the bond.

Vocabulary Metallic bonding Malleability Ductility