Metallic Bonding Intermolecular Forces

Basic metallic properties Malleable: metals can be shaped into thin sheets Ductile: metals can be drawn into wires. Metals are good conductors of electricity. Ionic solids are brittle Metals are good conductors of heat.

Properties of metals based on molecular structure Metal Ion (+) - close-packed in structure. - each atom surrounded by 8 to 12 adjacent atoms - e- are mobile not confined to any particular metal ion (0 electrostatic attraction) evenly distributed Electron-Sea Model

Crystalline Structure of a Metal 1.Body-centered Cubic: Every atom (except those on the surface) has 8 neighbors 2.Face-centered Cubic: Every atom has 12 neighbors 3.Hexagonal close packed: Every atom has 12 but different pattern due to hexagonal

Alloy: material that contains more than 1 element and has characteristic properties of metals. Primary method of modifying properties of pure metals Brass (Zn & Cu) Steel (Fe & C)

Why use alloys? Properties are often superior to the pure element Sterling silver (92.5% Ag, 7.5% Cu) is harder and more durable than pure Ag, but still soft enough to make jewelry and tableware Steels are very important alloys corrosion resistant, ductility, hardness, toughness, cost Properties are often superior to the pure element Sterling silver (92.5% Ag, 7.5% Cu) is harder and more durable than pure Ag, but still soft enough to make jewelry and tableware Steels are very important alloys corrosion resistant, ductility, hardness, toughness, cost

More about Alloys… Types? a) substitutional alloy- the atoms in the components are about the same size b) interstitial alloy- the atomic sizes quite different; smaller atoms fit into the spaces between larger “Amalgam”- dental use, contains Hg Types? a) substitutional alloy- the atoms in the components are about the same size b) interstitial alloy- the atomic sizes quite different; smaller atoms fit into the spaces between larger “Amalgam”- dental use, contains Hg

Intermolecular forces are forces that exist between molecules. contribute to properties of solids, liquids, & gases weaker than ionic or covalent bonds Ex. melting & boiling point Intermolecular Forces

Types of intermolecular forces - Ion-dipole attractions - Dipole-dipole attractions - Hydrogen bonding - London dispersion forces

Ion-dipole attractions They occur between an ion and the partial charge on the end of a polar molecule.

Dipole-dipole attractions These forces occur when neutral polar molecule attract each others. + & - ends are in close proximity to each other Weaker than ion-dipole attractions

London dispersion forces Occur when a temporary dipole is induced on a nonpolar molecule/atom by e- from another nonpolar molecule/atom. Ex. He (g)

Hydrogen Bonding H-bonding is a special type of intermolecular attraction between the H atom in a polar bond and a nonbinding e - pair on a small electronegative ion or atom Typical H-bonding pairs include:H-O H-F H-N

H-bonding in H 2 O causes hexagonal cavities to form in its solid state. Due to increased distance between molecules. H 2 O expands when frozen H 2 O is less dense when frozen