STRUCTURAL EFFECTS ON SOLUBILITY, MELTING POINT, AND BOILING POINT

INTERMOLECULAR FORCES

attractive forces between molecules

• van der Waals

• Hydrogen bonding

• Ion-dipole interaction

INTERMOLECULAR FORCES types 3

INTERMOLECULAR FORCES

All _ are electrostatic, involving attractions

between positive and negative species.

electrostatic attraction

interaction between positive and negative charge

INTERMOLECULAR FORCES

are the forces that hold molecules in a substance

INTERMOLECULAR FORCES

Weaker than intramolecular forces

INTERMOLECULAR FORCES

Determine the state of matter (solid/liquid/gas) and their physical properties such as melting/boiling point etc.

INTERMOLECULAR FORCES

Attractive forces

INTERMOLECULAR FORCES

Categorized into dipole-dipole forces, London dispersion forces and hydrogen bonding forces

INTRAMOLECULAR FORCES

are the forces that hold atoms in a molecule

INTRAMOLECULAR FORCES

Stronger than inte

rmolecular forces

INTRAMOLECULAR FORCES

Determine chemical behavior of a substance

INTRAMOLECULAR FORCES

Chemical bonds

INTRAMOLECULAR FORCES

Categorized into covalent, ionic and metal bonds

Strong intramolecular attraction (covalent bond)

Weak intermolecular attraction

intramolecular force/attraction (covalent bond)

within one molecule of hcl there’s an _

intramolecular force

chemical bonds

intermolecular force

between molecules there’s an _

London

Debye

Keesom

Van der Waals forces 3 types

London

dispersion forces (induced dipole-induced dipole)

Debye

dipole-induced dipole

Keesom

dipole-dipole

INTRAMOLECULAR FORCES

ability to particaipte in a chemical reaction

INTERMOLECULAR FORCES

ARE MORE IMPORTANT/RELEVANT

LONDON DISPERSION FORCE

a.k.a. induced dipole-induced dipole interactions

LONDON DISPERSION FORCE

attractive force that arises as a result of temporary dipoles induced in

atoms or molecules

LONDON DISPERSION FORCE

present in all substances (polar or nonpolar)

LONDON DISPERSION FORCE

weakest

LONDON DISPERSION FORCE

DISPERSION FORCE/DIPOLE-INDUCED DIPOLE

DIPOLE

SEPARATION OF CHARGES/ EXISTENCE OF 2 POLES WITH OPPOSITE CHARGES

LONDON DISPERSION FORCES

An instantaneous dipole (due to movement of electrons)

LONDON DISPERSION FORCES

momentary dipoles/temporary dipoles

nonpolar

even in _ substances, there can be temporary/momentary.instantaneous dipoles

In this initial state, the electrons in both atoms are evenly distributed around the nucleus. There's no separation of charge, meaning neither atom has a positive or negative pole.

Electrons are constantly moving. At any given instant, the electron distribution might become uneven in one atom (Atom B in this case). This creates a temporary, instantaneous dipole – one side becomes slightly negative (δ-) due to a momentary excess of electrons, and the other side becomes slightly positive (δ+).

The temporary dipole in Atom B affects the electron distribution in Atom A. The positive pole (δ+) of Atom B attracts the electrons in Atom A, causing them to shift and create an induced dipole in Atom A. This results in an electrostatic attraction between the positive pole of Atom A and the negative pole of Atom B.

repel

like charges will

induction

_ of dipole is due to the polarization of adjacent atom for molecules

LONDON DISPERSION FORCE

significant only when molecules are close together

LONDON DISPERSION FORCE

depends on area of contact: greater area of contact, stronger London

dispersion forces

greater

LONDON DISPERSION FORCE

depends on area of contact: _ area of contact, stronger London

dispersion forces

stronger

LONDON DISPERSION FORCE

depends on area of contact: greater area of contact, _ London

dispersion forces

Increase

_ in MW increases London dispersion force

increases

Increase in MW _ London dispersion force

Branching

_ decreases London dispersion force

increase MW

how to increase area of contact?

chain

longer _. longer area of contact

branching

_ decreases area of contact/london dispersion forces

KEESOM FORCE

a.k.a. dipole-dipole interaction

KEESOM FORCE

electrostatic attraction between the partially positive end of one

molecule and the partially negative end of a neighboring molecule

KEESOM FORCE

present in polar compounds (only)

KEESOM FORCE

stronger than London dispersion force

polar-polar

permanent dipole

non-polar

momentary dipoles

attractive dipole-dipole interaction (red); organized

repulsive dipole-dipole interaction (blue); randomly oriented

KEESOM FORCE

depends on polarity

polarity

KEESOM FORCE

Increase in _ increases dipole-dipole interaction

dipole-dipole interaction

KEESOM FORCE

Increase in polarity increases _

LONDON & KEESOM

both are van der Waals

Keesom

Even though _ is stronger, London is more significant in

determining the bulk properties of matter.

London

Even though Keesom is stronger, _ is more significant in

determining the bulk properties of matter.

bulk

Even though Keesom is stronger, London is more significant in

determining the _ properties of matter.

HYDROGEN BONDING

electrostatic attraction between a hydrogen attached to an

electronegative atom (N, O, F) and a lone pair of an electronegative

atom (N, O, F) in another molecule

HYDROGEN BONDING

a strong type of dipole-dipole interaction

N O F

HYDROGEN BONDING hydrogen attached to an

electronegative atoms (3)

HYDROGEN BONDING

depends on the electronegativity of atom interacting with hydrogen

HYDROGEN BONDING

special type of dipole-dipole; not classified under dipole-dipole; more impt contributor to the bulk properties

ION-DIPOLE INTERACTION

electrostatic attraction between an ion and a polar molecule

cation

_ with partially negative end of polar molecule

anion

_ with partially positive end of polar molecule

electrostatic attraction

H is partially positive; N, O, F are partially negative

ION-DIPOLE INTERACTION

present in ionic compounds dissolved in polar solvents

ION-DIPOLE INTERACTION

strongest

>

HF _ H2O - NH3

ion-dipole interaction

one is ionic; one is a polar compound

ION-DIPOLE INTERACTION

depends on ionic charge and polarity

covalent

in org chem, most compounds are not ionic they’re

ION-DIPOLE INTERACTION

The positively charged sodium ion (Na+) attracts the partially negative (δ-) oxygen ends of the water molecules. This aligns the water molecules around the sodium ion with their oxygen atoms pointing towards it.

ION-DIPOLE INTERACTION

The negatively charged chloride ion (Cl-) attracts the partially positive (δ+) hydrogen ends of the water molecules. This aligns the water molecules around the chloride ion with their hydrogen atoms pointing towards it.

van der waals and hyrogen bonding

most impt imf 2 in our discussion

Dispersion forces (London Dispersion Forces)

• Weakest IMF.

• Present in all substances.

• Become stronger with larger molecules.

• Examples: CH₄, Br₂.

• Energies: 0.1-30 kJ/mol.

Dipole-dipole forces

• Occur between polar molecules.

• Stronger than dispersion forces.

• Examples: CH₃F, HBr.

• Energies: 2-15 kJ/mol.

Hydrogen bonding

• A special type of dipole-dipole force.

• Occurs when H is bonded to N, O, or F.

• Relatively strong IMF.

• Examples: NH₃, CH₃OH.

• Energies: 10-40 kJ/mol.

Ion-dipole forces

• Occur between ions and polar molecules.

• Stronger than hydrogen bonding.

• Examples: NaCl dissolved in H₂O.

• Energies: >50 kJ/mol.

Ionic bonding

• Not strictly an IMF, but a strong chemical bond.

• Occurs between ions in ionic compounds.

• Strongest interaction.

• Examples: KBr, NH₄NO₃.

• Energies: >150 kJ/mol.

Dispersion forces

occur in all molecules but are dominant in nonpolar molecules.

Dipole-dipole forces

exist in polar molecules without hydrogen bonding.

Hydrogen bonding

occurs when H is bonded to N, O, or F.

Ion-dipole forces

happen when ionic compounds dissolve in polar solvents.

Ionic bonding

is the strongest and occurs between fully charged ions.

Dispersion Forces (0.1–30 kJ/mol)

Present in all molecules and atoms (weakest interaction).

Dispersion Forces (0.1–30 kJ/mol)

Applies to: Atoms (Ne, Ar), Nonpolar molecules (BF₃, CH₄), Polar molecules (HCl, CH₃CN, H₂O, NH₃).

Dipole-Dipole Interactions (2–15 kJ/mol)

Occur in polar molecules without hydrogen bonding.

Dipole-Dipole Interactions (2–15 kJ/mol)

Applies to: Polar molecules without OH, NH, or HF groups (HCl, CH₃CN), and Polar molecules containing OH, NH, or HF groups (H₂O, NH₃).

Hydrogen Bonding (10–40 kJ/mol)

Strong interaction found in polar molecules containing OH, NH, or HF groups.

Hydrogen Bonding (10–40 kJ/mol)

Applies to: Molecules like H₂O and NH₃.

Ion-Dipole Interactions (>50 kJ/mol)

Strong force between ions and polar molecules.

Ion-Dipole Interactions (>50 kJ/mol)

Applies to: Ionic solids dissolved in polar liquids (e.g., NaCl in H₂O).