GENERAL CHEMISTRY 2
- Review of key concepts in General Chemistry 2.
KINETIC MOLECULAR THEORY
Postulates of Kinetic Molecular Theory (KMT)
- Matter is comprised of particles that are constantly in motion.
- The energy associated with this movement is termed kinetic energy.
- The amount of kinetic energy present in a substance correlates to its temperature.
- Particles are separated by space, with the amount of separation relating to the substance's state of matter.
- Phase changes occur when the temperature of a substance changes sufficiently.
- Attractive forces exist between particles, known as intermolecular forces, where the strength of these forces increases as particles come closer together.
PARTICLE ARRANGEMENT IN PHASES OF MATTER
Solid
- Particles are tightly packed in a fixed arrangement.
Liquid
- Particles are close together but lack a distinct arrangement; particles can slide over one another.
Gas
- Particles are free-floating with no distinct arrangement.
INTRAMOLECULAR FORCES OF ATTRACTION
- Atoms within a molecule or ionic substance remain attracted through chemical bonds.
- These bonds can either be covalent or ionic and are termed intramolecular forces.
TYPES OF INTRAMOLECULAR FORCES
Chemical Bonds
- Ionic Bond
- Covalent Bond
- Polar Covalent Bond
- Nonpolar Covalent Bond
- Metallic Bond
POLARITY OF MOLECULES AND MOLECULAR GEOMETRY
Overview
- For polyatomic molecules, both bond polarity and molecular shape determine the overall molecular polarity.
- Valence Shell Electron Pair Repulsion (VSEPR) theory is utilized to predict the spatial arrangement of atoms in a polyatomic molecule.
Steps to Predict Molecular Geometry
- Identify the central atom (the least electronegative element).
- Construct the Lewis dot structure for the molecule.
- Count the number of bonding pairs and lone pairs around the central atom.
- Determine the electron pair orientation based on the total number of electron pairs.
- Identify the shape of the molecule according to the atom locations.
FLOWCHART FOR POLARITY DETERMINATION
- Is the shape symmetrical in 3D?
- NO: The molecule is POLAR.
- YES: Are all atoms bonded to the central atom the same?
- NO: The molecule is POLAR.
- YES: The molecule is NONPOLAR.
Polar vs. Nonpolar Molecules
- Nonpolar Molecules:
- Equal on all sides.
- Symmetrical shape around central atom.
- Polar Molecules:
- Not equal on all sides.
- Asymmetrical shape around central atom.
CHEMICAL BONDS
- Types of Chemical Bonds:
- Ionic Bond
- Covalent Bond
- Metallic Bond
- Polar Covalent Bond
- Nonpolar Covalent Bond
- Van der Waals Forces
- H-Bonding
- Ion-Dipole Interaction
- Dipole-Dipole Interaction
- Dipole-Induced Dipole Interaction
- London Dispersion Forces
TYPES OF INTERMOLECULAR FORCES
- Van der Waals Forces:
1. Dipole-Dipole Interaction
- Attractive forces between polar molecules; involves a partial positive charge of one molecule attracting a partial negative charge of another.
2. Dipole-Induced Dipole Interaction
- Occurs when a polar molecule induces a dipole in a nonpolar molecule by disturbing its electron arrangement.
3. London Dispersion Forces
- Weak attractions occurring between neutral and electrically symmetric molecules.
4. Hydrogen Bonding
- A specific type of dipole-dipole interaction involving an H atom bonded to highly electronegative atoms like N, O, or F, forming hydrogen bonds with other molecules.
ION-DIPOLE INTERACTION
- Results from electrostatic interaction between charged ions and polar molecules characterized by their dipoles.
- For example, the partially negative charge of oxygen in water is attracted to a positive sodium ion ( ext{Na}^+).
DETERMINING INTERMOLECULAR FORCES
Examples
- HCl and HCl: Dipole-Dipole Interaction (polar)
- N2 and N2: London Dispersion Force (nonpolar)
- H2O and Cl: Ion-Dipole Interaction
- NH3 and NH3: H-Bonding
- CH4 and CO: Dipole-induced Dipole Interaction
IMPORTANCE OF KNOWING INTERMOLECULAR FORCES
- Understanding intermolecular forces (IMFA) helps in explaining and predicting the physical properties of substances.
RELATIVE STRENGTH OF INTERMOLECULAR FORCES
- Strongest: Ion-Dipole Interaction
- H-Bonding Interaction
- Dipole-Dipole Interaction
- Dipole-Induced Dipole Interaction
- Weakest: London Dispersion Force
PROPERTIES AFFECTED BY IMFA
Surface Tension
- A liquid's surface resists external forces due to cohesive forces among its molecules; higher IMFA correlates with higher surface tension.
Capillary Action
- The ability of a liquid to ascend against gravity due to cohesive and adhesive forces.
Viscosity
- A measure of a liquid's resistance to flow; greater viscosity indicates stronger IMFA.
- Higher IMFA results in slower flow.
Boiling Point
- The temperature at which a liquid transitions to vapor; correlates with intermolecular forces—the stronger the forces, the higher the boiling point.
Boiling Point Examples
- Water (H2O): 100°C - H-Bonding
- Methane (CH4): -162°C - London Dispersion Force
- Chloroform (CHCl3): 61.2°C - Dipole-Dipole
Melting Point
- The temperature at which a substance transitions from solid to liquid under atmospheric pressure.
Melting Point Examples
- Water (H2O): 0°C - H-Bonding
- Methane (CH4): -182°C - London Dispersion Force
- Chloroform (CHCl3): 65.3°C - Dipole-Dipole
Solubility
- The ability of a substance to dissolve in another; dependent on molecular interactions, pressure, and temperature.
Solubility Principle
- "Like dissolves like": Nonpolar solutes dissolve in nonpolar solvents; polar solutes dissolve in polar solvents.
- Nonpolar compounds are generally insoluble in polar solvents.
MATERIALS REQUIRED FOR EXPERIMENTS
- Liquid samples: water, ethyl alcohol, kerosene
- Beakers or glass jars with wide mouth
- Small piece of wax paper or plastic sheet
- Old newspapers for drips/spills
- Plastic straw
- Salt
- Sugar
- Three droppers
- Three blades
- Glass jar
- One-peso coins
- Plastic sheet
- Pepper
- Talcum powder