LECTURE 7.1

LECTURE OUTLINE Weekly Deadlines. Weekly Deadlines. The Metallic Bond The Metallic Bond The van der Waals Bond The van der Waals Bond The Hydrogen Bond The Hydrogen Bond

THE METALLIC BOND The bonds formed between an array of positively charged metallic cations and a "sea" of negatively charged, free-electrons, the latter being "donated" from the outer shells of the constituent atoms. The bonds formed between an array of positively charged metallic cations and a "sea" of negatively charged, free-electrons, the latter being "donated" from the outer shells of the constituent atoms. Metallic bonds are non-directional. Metallic bonds are non-directional. Occurs for all metallic elements and their alloys (i.e., Group I, I and III metals and for the transition metals), to form close-packed solids Occurs for all metallic elements and their alloys (i.e., Group I, I and III metals and for the transition metals), to form close-packed solids

METALLIC BOND Metallic Bond: arises from the electrostatic attraction between cation cores and an electron cloud. The electrons are said to be delocalized, because they are not confined, to any cation core, but are “free” to move between the cation cores. Hence, the metallic bond is non-directional.

METALLIC BONDING

CUBIC CLOSE PACKING I

CUBIC CLOSE PACKING II

CUBIC CLOSE PACKING III

BODY CENTERED CUBIC

THE THREE COMMON METALLIC CRYSTAL STRUCTURES

VAN DER WAALS BOND Weak, secondary bonds formed by the attraction of fluctuating dipoles between e.g., atoms of the noble gases, and between molecules. van der Waals bonds are non-directional. Weak, secondary bonds formed by the attraction of fluctuating dipoles between e.g., atoms of the noble gases, and between molecules. van der Waals bonds are non-directional.

THE VAN DER WAALS BOND

THE VAN DER WAALS BOND AND POLYETHYLENE

HYDROGEN BOND Weak, secondary bonds formed by the attraction of polar molecules. A polar molecule (or dipole) results from a permanent imbalance in the electron distribution in a molecule, between an electronegative atom (e.g., oxygen) and an electropositive atom (e.g., hydrogen). Hydrogen bonds are directional. Weak, secondary bonds formed by the attraction of polar molecules. A polar molecule (or dipole) results from a permanent imbalance in the electron distribution in a molecule, between an electronegative atom (e.g., oxygen) and an electropositive atom (e.g., hydrogen). Hydrogen bonds are directional.

THE COVALENT BOND AND WATER The water molecule consists of one oxygen atom, covalently bonded to two hydrogen atoms. The water molecule consists of one oxygen atom, covalently bonded to two hydrogen atoms. However, the oxygen atom attracts the shared electron pairs more strongly than do the hydrogen atoms, and the shared electrons “spend more time” with the oxygen atom. Hence, a permanent dipole develops, with slightly positive charges on the hydrogen atoms, and slightly negative charges on the oxygen atoms. However, the oxygen atom attracts the shared electron pairs more strongly than do the hydrogen atoms, and the shared electrons “spend more time” with the oxygen atom. Hence, a permanent dipole develops, with slightly positive charges on the hydrogen atoms, and slightly negative charges on the oxygen atoms.

THE HYDROGEN BOND, AND THE CRYSTAL STRUCTURE OF ICE The monomer of the ice structure consists of a central, covalently bonded molecule of water, which is hydrogen bonded to four other water molecules. The monomer of the ice structure consists of a central, covalently bonded molecule of water, which is hydrogen bonded to four other water molecules. When the monomers are assembled to create the crystal structure of ice, a hexagonal material results. When the monomers are assembled to create the crystal structure of ice, a hexagonal material results.

MAKING SNOWBALLS

THE “SURFACE” STRUCTURE OF ICE

THE SPECIFIC GRAVITY/VOLUME OF WATER

THE ANOMOLOUS COOLING BEHAVIOR OF WATER

THE SPECIFIC VOLUME OF WATER

HYDROGEN BONDING AND THE MELTING/BOILING POINTS OF WATER

A COPMPARISON OF ICE WITH OTHER “OXIDES”