6 - Intermolecular Forces and Lab Techniques

These flashcards cover key vocabulary and concepts related to intermolecular forces and their properties in chemistry.

Intramolecular Forces

Forces that bond different atoms within a molecule.

• (Strongest to Weakest) Ionic, Covalent, Metalic

Polarimetry

Technique used to measure the optical activity or Chirality of a compound

Silver nitrate in Alcohol Test

A qualitative test used to identify the presence of alkyl halides (Cl, Br, or I) in organic compounds.

• Reagents: AgNO3 in alcohol

• Positive Result: An opaque precipitate of Ag compound formed (color varies by halide)

Eluent

Nonpolar solvent commonly used in column chromatography to flush the mixture through the column, aiding in separation of compounds.

Gas-Liquid Chromatography

Where a gas mobile phase carries vaporized samples through a tube coated with a liquid stationary phase.

• Separation is based on BPs and a molecules polarity.

  • Lower BPs and Non-polar molecules usually elute first

What is the best way to separate a carboxylic acid from an amine?

Extract the Carboxylic acid into aqueous NaOH

Intermolecular Forces

Forces that bind separate, individual molecules together.

• (Strongest to Weakest) Hydrogen bonding, Dipole-Dipole, Dispersion Forces

How does branching affect BP of molecules with same molecular weight and same IM forces?

• As branching Increases, the boiling point decrease (Indirect)

How does branching affect MP of molecules with the same molecular weight and same IM forces?

• Usually as branching increases, MP increase (DIrect)

• Except: For straight chains (with no branching) which should be the highest MP

As intErmolecular forces increase, what happens to boiling point, melting point, and vapor pressure?

Hydrogen Bonding > Dipole-Dipole > Dispersion Forces

• BP increases (Direct)

• MP increases (Direct)

• Vapor Pressure Decreases (Indirect)

Which force is stronger: Intramolecular or Intermolecular forces?

IntrAmolecular Forces

Identify the Metals, Non Metals, and Metalloids in the periodic table

Does Hydrogen bonding increase boiling point?

Yes

Covalent Bond

A bond formed when two or more non-metal atoms share electrons.

Ionic Bond

A bond formed when metals transfer electrons to non-metals, creating ions.

• Formed Between Metal and Non-Metal Atoms

Metallic Bond

A bond formed when metal atoms allow their electrons to flow freely.

Covalent Network Solid

A non-metal solid made of a network of covalent bonds,

• Diamond, Quartz

Ionic Solid

A solid made of ionic bonds

• high melting point

• brittle.

Hydrogen Bonding

A strong intermolecular force occurring between molecules that have hydrogen bonded to N, O, F.

Dipole-Dipole Forces

Attractive forces between polar molecules.

• Cause a partial positive and partial negative charge

• Only occur in polar, non-ionic molecules, that do not have H bonded to N,O,F

Dispersion Forces

Weak intermolecular forces arising from temporary shifts in electron density.

Ion-Dipole Forces

Forces that occur between ionic compounds and polar molecules.

Hydrogen Bonding Examples

Examples include H-O, H-N, and H-F bonds.

Molecular Compounds

Compounds that only have covalent bonds.

Cation

A positively charged ion formed when a metal loses an electron.

Anion

A negatively charged ion formed when a non-metal gains an electron.

Examples of Ionic Compounds

Sodium chloride (NaCl), Silver chloride (AgCl).

Bonding Forces

Forces that hold atoms together within a molecule.

Polar Molecule

A molecule with a net dipole moment due to unequal sharing of electrons.

Nonpolar Molecule

A molecule that does not have a net dipole moment.

Chemical Properties of Metals

Metals generally conduct electricity and heat, have high melting and boiling points.

Intrinsic Properties

Properties that do not depend on the amount of material present.

Extrinsic Properties

Properties that depend on the amount of material present.

Solubility Principle

Like dissolves like; polar substances dissolve in polar solvents.

Homogeneous Mixture

A mixture that has a uniform composition throughout.

Heterogeneous Mixture

A mixture that has a non-uniform composition.

Extraction Method

A technique used to separate compounds based on solubility.

Aqueous Layer

The layer of water in a separatory funnel after extraction.

Organic Layer

The layer containing organic solvents in a separatory funnel.

Distillation

A technique used to separate mixtures based on boiling points.

• Based on boiling points

• Best used when the difference in boiling points is greater than 25C

Fractional Distillation

Distillation used for separating liquids with close boiling points.

• Like doing multiple simple distillations

• Best used when the difference in boiling points are at about 25C

Sublimation

The process of a solid turning directly into gas.

• can be used for purification

Recrystallization

A technique for purifying solid compounds.

• Best used when desired solid is less soluble in the solvent than the impurities

• Best used with non volatile solids

Thin-Layer Chromatography (TLC)

A technique used to separate and analyze compounds based on polarity.

• Plate and spotting method

• Used to separate non-volatile substances

• Separates molecules based on polarity

  • The higher the spot the less polar the substance is and the lower the spot the more polar it is

Retention Factor (Rf)

The ratio of the distance traveled by the compound to the distance traveled by the solvent.

• = Distance of spot traveled / Distance of solvent traveled

• Values are solvent specific; may change is solvent is changed

Column Chromatography

A method for separating compounds based on their polarity.

• Most non-polar compound travels the fastest with the slowest being the most polar compound

Tollens’ Test

A qualitative test for determining if aldehydes are present

• Reagents: Ag2O / NH3 or Ag(NH3)2

• Positive Result: Sides of flask are coated in silver mirror

Iodoform Test

A qualitative test for determining if methyl ketones (Ketone with one CH3 group attached) are present

• Reagents: I2/OH

• Positive Result: Forms a yellow precipitate

Bromine Test

A test to determine the presence of alkenes and alkynes.

• Reagents: Br2/CCl4

• Positive Result: Brown color of bromine disappears and solution should be clear

Jones Test

A test for determining the presences of primary and secondary alcohols.

• Reagents: CrO3 / H2SO4

• Positive test: Orange reagent turns blue-green

Electrolyte

A substance that produces an electrically conducting solution when dissolved.

Melting Point

The temperature at which a solid becomes a liquid.

Boiling Point

The temperature at which a liquid turns into vapor.

Vapor Pressure

The pressure exerted by a vapor in equilibrium with its liquid at a given temperature.

Electronegativity

A measure of the tendency of an atom to attract a bonding pair of electrons.

Carboxylic Acid

An organic compound containing a carboxyl group (-COOH).

Phenol

An aromatic compound with a hydroxyl (-OH) group.

Amine

A compound that contains a basic nitrogen atom.

Polar Solvent

A solvent that has a net dipole moment, such as water.

Nonpolar Solvent

A solvent that does not have a net dipole moment.

Brittle

A material that breaks easily under stress.

Conductive

A characteristic of materials that can conduct electricity.

Soluble

Capable of being dissolved in a solvent.

Insoluble

Incapable of being dissolved.

Charaterization

The process of identifying and verifying the properties of a compound.

Solubility

The ability of a substance to dissolve in a solvent.

Chemical Purity

The absence of impurities in a substance.

Silica Gel

Tiny polar beads commonly used in column chromatography.

Glassware

Equipment made of glass used in chemical laboratories.

Organic Chemistry

The study of the structure, properties, composition, reactions, and synthesis of organic compounds.

Functional Group

A specific group of atoms within a molecule that is responsible for a characteristic of that compound.

Chemical Reaction

A process that leads to the transformation of one set of chemical substances into another.

Thermal Decomposition

The breakdown of a compound due to heat.

Solution

A homogeneous mixture composed of two or more substances.

Precipitation

The process of settling of solids from a solution.

Catalyst

A substance that increases the rate of a reaction without being consumed.

Stoichiometry

The calculation of reactants and products in chemical reactions.

Oxidation

A chemical reaction that involves the transfer of electrons, resulting in an increase in oxidation state.

Reduction

A chemical reaction that involves the gain of electrons, resulting in a decrease in oxidation state.

Acid-Base Reaction

A reaction that occurs between an acid and a base.

Deprotonation

The removal of a proton (H+) from a molecule.

Protonation

The addition of a proton (H+) to a molecule.

Electrophile

A reagent attracted to electrons that seeks to react with nucleophiles.

Nucleophile

A chemical species that donates an electron pair to form a chemical bond.

Chemical Bonds

The attractive forces that hold atoms together to form molecules.