Unit 4.3 Intermolecular Forces & Metallic Bonding

Intermolecular Forces (IMF)

Forces of attraction between molecules that hold them together.

Dispersion Forces

Forces that result from the motion of electrons in an atom, creating temporary dipoles.

Dipole-dipole Attractions

Attractive forces between molecules with permanent dipoles.

Hydrogen Bonding

A special type of dipole-dipole attraction that occurs when a hydrogen atom is bonded to a highly electronegative atom (O, N, or F) and forms a bond with the lone pair of electrons on another molecule.

Hydrogen Bond Donors and Acceptors

Every hydrogen bond has two components - a donor (the molecule with the hydrogen atom) and an acceptor (the molecule with the lone pair of electrons).

Melting and Boiling Point

The temperature at which a substance changes from a solid to a liquid or from a liquid to a gas, respectively. The strength of intermolecular forces affects the melting and boiling points of covalent compounds.

Solubility

The ability of a substance to dissolve in a solvent. "Like dissolves like" - polar substances dissolve in polar solvents, while non-polar substances dissolve in non-polar solvents.

Conductivity

The ability of a substance to conduct electricity. Covalent compounds usually do not conduct electricity, except for some polar covalent molecules and giant covalent structures.

Metallic Bonding

Bonding between metal atoms in which the outer electrons are delocalized and can move freely throughout the entire structure.

Properties of Metals

Metals are malleable, have high melting and boiling points, and can conduct electricity due to the presence of delocalized electrons.

Strength of Metallic Bonds

The strength of metallic bonds depends on the charge on the metal ion and the radius of the metal ion.

Trends in Melting Points of Metals

The melting points of metals increase across a period and decrease down a group due to changes in the strength of electrostatic attraction caused by the number of delocalized electrons, positive charges on the metal centers, and size of the metal ions.

Alloys

Mixtures of metals or metals and non-metals that have distinct and desirable properties due to the different sizes and arrangements of cations in the lattice structure.

Alloy Properties

Alloys are stronger, harder, and more resistant to corrosion and extreme temperatures compared to pure metals.

Common Alloys & their Uses

Examples of alloys include brass (copper + zinc), steel (iron + carbon + others), solder (lead + tin), and bronze (copper + tin), which are used in various applications such as door handles, construction, electrical circuits, and sculptures.