Intermolecular forces 10/6

Intermolecular forces

The forces that keep molecules together in a solid and liquid that are overcome to change to a different state of matter (ex. liquid). Non-covalent interactions between molecules or other particles.

Viscosity

a measure of a fluid's resistance to flow, of resistance of a fluid to be deformed, of friction between molecules of a fluid. One of the results of intermolecular forces along with boiling point and vapor pressure (the equilibrium pressure exerted by a vapor that measures the tendency of a material to change into the gaseous or vapor state). Higher intermolecular forces means increases viscosity.

London dispersion forces

temporary attractive force due to the formation of temporary dipoles in a nonpolar molecule. When the electrons in two adjacent atoms are displaced in such a way that atoms get some temporary dipoles, they attract each other through the London dispersion force. Due to random fluctuations in e- density. Their strength increases when molar mass increases (bigger e-cloud—polarizability) and when species become more elongated (surface area)

Dipoles

A bond or molecule whose ends have opposite charges

Dipole-dipole interactions

Present in POLAR particles with permanent but incomplete separation of charges. The partial charges formed within one molecule are attracted to an opposite partial charge in a nearby molecule. Weak interactions.

T or F: molecules in a polar compound are more strongly attracted than in non-polar compounds?

T

Why does the boiling point of alkanes (single C-C nonpolar bonds) increase with size (molecular mass) of the molecule?

Due to the stronger the intermolecular forces, specifically London dispersion forces. The larger the molecule, the more electrons in these dispersion forces so the more easily these temporary dipoles form.

Hydrogen bonds

A type of dipole-dipole interaction with strong directionality involving polar hydrogens

Electrostatic interactions (ion-ion)

Present in particles with permanent and total separation of charges. Interactions between atoms or molecules with a permanent charge:ions. They are typical in ionic compounds.

Lattice energy

The energy of interactions of ions in a crystal, with the symbol U. It depends on the size of the ions (the larger the “r” in the coulombic energy formula the less the lattice energy) and the magnitude of the ionic charge (the higher the lattice energy the higher the magnitude of the charges)

Crystal

Ions will arrange into a continuous and alternating array of positive and negative ions

permanent dipole moment

When two atoms in a molecule have different electronegativities, the more electronegative atom will attract electrons away from the less electronegative atom. This will create a permanent separation of charges.

Total separation of charges meaning?

the transfer of an electron from one atom (electron is excited to a higher energetic level leaving the atom positively charged) to another as an ionic bond is formed

Ion-dipole interactions

Involving interactions between particles with permanent and total charge separation and those with permanent but incomplete separation of charges. An attractive force between an ion and a molecule that has a permanent dipole. These interactions chase ionic compounds to dissolve in water.

incomplete separation of charges

partial charge difference due to unequal sharing of electrons

Permanent charge separation

a constant uneven distribution of electrons in a molecule, resulting in a permanent dipole moment. This happens when atoms in a molecule have different electronegativities, causing electrons to be unevenly shared

Charge and size of positive ions patterns in P.T.

The charge of positive ions increases as you move in the same row from left to right. The size of positive ions decreases from left to right in the same row.

Energy and coulombic attraction (E in equation) relationship

The larger the charge (ex. -2>-1) the higher the coulombic attraction in a compound is

Hydrogen bond

Electrostatic force of attraction between a hydrogen atom which is covalently bound to a more electronegative atom or group, particularly N, O, F. Has a dipole-dipole interaction. The strands of a DNA double helix are kept together by H bonds.

H bond donor vs H bond acceptor

D: the atom that hydrogen is covalently bonded to

A: the atom with the lone electron pair forming the “bond” to the hydrogen bond

Spheres of hydration

When ions are dissolved in water they are surrounded by oriented layers of solvent called spheres of hydration. Created a stabilizing environment for the ion.

Solubility

The maximum quantity that can dissolve in a given volume of solution.

Solution

a homogeneous mixture of 2 or more substances. Dépendes in the type and number of interactions between solvent and solute molecules.

Miscible liquids

Two liquids that are soluble in one another in any proportion, for example, water and ethylene glycol because water is able to form hydrogen bonds with ethylene glycol

Hydrophobic vs hydrophilic

Less soluble (ex. For Ketones as the length of the carbon chain increases) and more soluble (for small ketones bc the dipole-dipole interactions promote solubility)

Surface tension

Ability of surface of a liquid to resist an external force. Increases when intermolecular forces increases. Causes a spherical form in water droplets. An object must overcome the surface tension of a liquid to penetrate the surface.

Gas and plasma phase changes

Gas to plasma= ionization

Plasma to gas= recombination

Allotropy

When the solid phase on an element can exist in different forms (ex. Sulfur exists as 2 different forms bc of try way molecules are packed when the solid was formed). Each form of the elements is called an allotropic form or allotropic.

Phase boundaries/Coexistence lines

The lines separating the different regions in a phase diagram. A point on the phase diagram line shows the pressure and temperature at which the two phases coexist in equilibrium under those conditions.

Def of Vapor pressure of the liquid

A liquid in empty vessel at some temperature T will evaporate until it reaches a certain pressure (the vapor pressure). Vapor pressures increase with temperature bc more molecules have the necessary energy to escape the condensed phase.

Sublimation vapor pressure

The solid-vapor (gas) boundary phase line that shows the vapor pressure of the solid at that temperature

Boiling

When the temperature is such that the vapor pressure equals the external pressure will it be possible for vaporization to occur through the bulk of the liquid and for the vapor to expand freely into the surroundings. This condition of free vaporization is called boiling.

The triple point

The only point where all three phases coexist. Occurs at specific Temperature and Pressure

Critical point

Where the liquid-gas equilibrium ends (there’s a critical pressure and critical temperature at the point). Beyond this point, there is a phase called the supercritical fluid that has both liquid and gas properties. There is no difference between the phases at the critical point of a liquid-vapor so only the critical density exists.

Supercritical fluid

Any substance at the temperature and pressure above is critical point. It can dissolve like a liquid and penetrate through solids like a gas (permeation). Used often for extractions from solid phases.