Thomson's Plum Pudding Model of the Atom

Atomic Models

• Thomson's model of the atom: electrons in homogeneous spheres of positive charge (plum-pudding model)
• Thomson's model limitations: only determined relative charge-to-mass ratio of electron and proton
• Robert Millikan's contribution: determined actual charge on the electron, allowing Thomson to calculate actual mass of electron and proton

Rutherford's Alpha Particle Experiment

• Rutherford's experiment: firing alpha particles at thin gold foils
• Unexpected observation: alpha particles deflected at large angles, contradicting the plum-pudding model
• Rutherford's conclusion: alpha particles are helium atoms that have lost all their electrons

Metallic Bonding

• Electron sea model: positively charged metal atoms embedded in a sea of shared electrons
• Characteristics of metals: low to moderate hardness, very malleable and ductile, soluble in acids, good thermal and electrical conductors

Chemical Equilibrium

• Chemical equilibrium: a dynamic, reversible process where reactants and products are constantly being formed
• Equilibrium constant expression: [B] / [A]^2
• Equilibrium constant (K): a measure of the ratio of concentrations of products to reactants at equilibrium

Equilibrium Expressions Involving Pressures

• For gases: PV = nRT or P = CRT / V
• Equilibrium constant expression for gases: KP = KC.RT^Δn
• Δn: the difference between the number of moles of products and reactants

Heterogeneous Equilibria

• Heterogeneous equilibrium: a reaction where one of the substances is in a different physical state
• Equilibrium constant expression: concentrations of liquids and solids are omitted
• Example: CaCO3(s) ⇌ CaO(s) + CO2(g)

Shifts in Gaseous Equilibria

• Le Chatelier's principle: the equilibrium shifts to relieve the stress when a reversible reaction is disturbed
• Effect of concentration: increasing the amount of reactants or products shifts the equilibrium to the right or left
• Effect of temperature: increasing the temperature favors the endothermic reaction, while decreasing the temperature favors the exothermic reaction
• Effect of pressure: increasing the pressure favors the reaction with fewer gas molecules

Wettability

• Wettability: a measure of the ease at which liquids spread on solid surfaces
• Contact angle measurement: a method to determine wettability
• Ideal solid surface: flat, rigid, perfectly smooth, chemically homogeneous, and has zero contact angle hysteresis
• Real surfaces: unlike ideal surfaces, they do not have perfect smoothness, rigidity, or chemical homogeneity

Cohesion and Adhesion

• Wettability as a balance between cohesion and adhesion
• Cohesion: the tendency for similar molecules to attract each other
• Adhesion: the degree to which dissimilar molecules attract each other