Chapter 10 - Liquids, Solids, Chromatography, & IMFs

What is an intramolecular force?

bonding within the molecule; ionic, covalent, metallic, network covalent; molecules are formed by transferring/sharing electrons between the atoms; significantly stronger than IMFs because it takes more energy to break bonds

What is an intermolecular force?

forces that are between molecules; Ion-dipole (strongest), dipole-dipole & hydrogen bonding, london dispersion forces

What happens to the bonds of a substance during a phase change?

The bonds remain intact; the change in state is due to the changes in the forces between the molecules rather than within the molecules

Ion-Dipole Forces

Between ions and polar molecules; Stronger than dipole-dipole interactions because the charge of any ion (whole #) is much greater than the charge of a dipole (fractional); the strength of ion-dipole interactions is dependent on the charge and distance (coulomb’s law); the ion-dipole force is proportional to ionic charge and dipole moment

Ion-Induced Dipole Forces

Between ions and nonpolar molecules; strength increases with larger charged ions, smaller ion size and more polarizable molecules

Dipole-Dipole Forces

Molecules with polar bonds often behave in an electric field as if they had a center of positive charge and a center of negative charge; molecules with dipole moments can attract each other electrostatically (positive and negative ends are close to each other); only about 1% as strong as intramolecular forces

Dipole-Induced Dipole Forces

Between polar and nonpolar molecules; strength of these forces increases with the magnitude of the dipole of the polar molecule and with polarizability of the nonpolar molecule

Hydrogen-bonding

Unusually strong dipole-dipole force; hydrogen is bound to highly electronegative atoms N, O, & F; the H on one molecule is attracted to the lone pair of electrons on a neighboring molecule; increases as electronegativity and the amount of areas for h-bonding increases

London Dispersion Forces

Occur in all molecules, but is the only IMF present in nonpolar molecules; more significant in large atoms/molecules with big electron clouds; instantaneous dipole occurs randomly in a given atom’s electron cloud which induces a similar dipole to a neighboring atom, creating a force of attraction; long hydrocarbons have stronger LDFs because it has a large surface area and more polarizable

What is polarizability?

the ability of an atom to form a temporary or induced dipole

How does the strength of IMFs affect the melting and boiling point of a substance?

The stronger the IMF(s), the higher the melting and boiling point of the substance

Liquids

Low compressibility, lack of rigidity, high density compared with gases, and experience surface tension and capillary action; liquids with large IMFs have high surface tension

Surface Tension

resistance of a liquid to an increase in its surface area; as IMFs increase, surface tension increases; surface molecules are pulled toward the interior; potential energy is increase for molecules at the surface; interior molecules are attracted in all directions

Capillary Action

spontaneous rising of a liquid in a narrow tube

Cohesive forces

IMFs amoung the molecules of the liquid

Adhesive Forces

Forces between the liquid molecules and their container

Amorphous Solids

Disorder in the structures

Crystalline Solids

Ordered structures; unit cells

Substitutional Alloy

Some of the host metal atoms are replaced by other metal atoms a of similar size (bond sizes are similar)

Interstitial Alloy

Some of the holes in the closest packed metal structure are occupied by small atoms (bond sizes vary); high melting and boiling point

Vapor Pressure

Pressure of the vapor at equilibrium; the system is at equilibirum when no net change occurs in the amount of liquid or vapor because the two opposite processes exactly balance each other

How does vapor pressure affect a substance?

Boiling point occurs when vapor pressure is equal or above atmospheric pressure; liquids with strong IMFs have relatively low vapor pressures

Volatile

the tendency of a substance to vaporize

Triple Point - Phase Change Diagram

conditions of temperature and pressure that allow all 3 phases of a substance to exist simultaneously (same for all substances except H2O)

Critical Point - Phase Change Diagram

the temperature and pressure at which the vapor and the liquids phases become indistinguishable

Phase Equilibrium Lines - Phase Change Diagrams

show what conditions of temperature and pressure allow for that specific state of matter

Molecular Solids

All non-metal atoms held by weak IMFs (lowest melting point)

Ionic Solids

Cations and anions held by ionic bonds

Metallic Solids

All metal atoms held by electron sea

Covalent Network Solids

Covalent bonds but in networks (large structure); highest melting point

As IMFs increase

BP increases, MP increases, viscosity increases, surface tension increases, enthalpy of fusion increases, freezing point increases, heat of vaporization increases, but vapor pressure decreases

Chromatography

provides a method of separating a mixture of solutions based upon polarity differences; the polarity differences are sometimes considered solubility as well; three types: paper, thin layer, and column

Paper Chromatography (most common in AP Chem)

The same compound will move at the same rate relative to the same solvent on different trials; different compounds will have at least slightly different polarity to other compounds so the R factor will differ between compounds; the more similar in polarity the sample is to the solvent, the farther it will travel; identification of a sample is possible by comparing R values - not comparing distances

Thin Layer Chromatography

used to separate some samples that are not colored to the human eye; same compound will move at the same rate relative to the solvent on different trials; different compounds will have an at least slightly different polarity to other compounds so the R factor will differ between compounds; the more nonpolar the sample is, the farther it will travel and vice versa;identification of a sample is possible by comparing R values - not comparing distances

Column Chromatography

the most polar parts of the mixture will travel the slowest and the least polar will travel the fastest; once you have separated one part you may use a new solvent to speed up the movement of the remaining part(s); this meant for separation more than analysis, so another type of chromatography will be used for identification

Distillation

separates mixtures based on differences in boiling point and intermolecular forces