Forces between Particles

Ionic vs. Covalent The higher the boiling point and melting point of a substance the stronger the forces between the particles Forces of attraction between ions is stronger than between molecules Ionic compounds have much higher boiling and melting points than covalent compounds

Ionic Compounds The smaller the ion the stronger the force of attraction Larger ions are farther apart so attractive forces are weaker

Intermolecular Forces Forces that act between molecules Van Der Waals forces Dipole-dipole forces Hydrogen bonding London Dispersion forces

Dipole-Dipole Forces Positive end of one molecule attracts the negative end of another molecule Charged ends of molecules result polar bonds The more polar the molecule, the stronger the dipole-dipole forces, the higher the melting and boiling point The bigger the difference of electronegativity of the atoms the more polar the bond

Hydrogen Bonds Special dipole-dipole force Stronger than regular dipole-dipole Involve H atoms and very electronegative atoms The H becomes partially positive and is attracted to unshared pairs of electrons on other molecules So strong because of high electronegativity difference and hydrogen’s small size

Properties of Water Some the result of H bonding Water can form multiple H bonds Solid less dense than liquid because of shape of molecule

London Dispersion Forces Special dipole-dipole force Act on nonpolar substances Larger molecules stronger forces Because larger number of electrons Temporary dipoles are created Briefly ends of a molecule can become (+) or (-) called induced dipoles Attraction between temporary dipoles holds the molecules together Very weak

Relative Strength Strongest to weakest Ionic attraction Covalent Bonding H bonding Dipole-Dipole London Dispersion

Properties of Compounds Determined by the IMF acting Stronger forces gives higher melting and boiling points Size and shape play a role Larger particles are farther apart, decreasing the strength of the forces The shape can keep things closer together or farther apart thus affecting the strength of the IMF

Surface Tension Force that acts on the surface of a liquid and that tends to minimize the area of a surface Most liquids make spheres because spheres have the lowest surface area per volume.

Cohesion/Adhesion Cohesion- liquid particles have an attraction for each other Adhesion- liquid particles have an attraction for particles of solid surfaces Combo of cohesion and adhesion create capillary action