Chemical Bonds and Intermolecular Forces
Chemical Bonds
Ionic Bonds
Ionic bonds involve the complete transfer of valence electron(s) between atoms, creating two oppositely charged ions. Metals lose electrons to become positively charged cations, while nonmetals gain electrons to become negatively charged anions.
Covalent Bonds
Covalent bonds form between atoms with similar electronegativities (affinity for electrons). Atoms share electrons to achieve a stable octet configuration.
Nonpolar Covalent Bonds
These bonds occur between identical atoms or atoms with very similar electronegativities (difference < 0.5).
Polar Covalent Bonds
These bonds typically form between two nonmetals with slightly different electronegativities (difference between 0.5 and 1.9). Examples include HCl, H2O, and HF.
Metallic Bonds
Metallic bonds occur between metal atoms, where valence electrons move freely through the lattice, creating a “sea of electrons.” The attraction between these mobile electrons and fixed metal ions forms the bond.
Relative Strength of Intramolecular Forces
| Intramolecular Force | Basis Information | Relative Strength |
|---|---|---|
| Metallic Bond | Metal cations to delocalized electrons | 1 (Strongest) |
| Ionic Bond | Cations to anions | 2 |
| Polar Covalent Bond | Partially charged cation to partially charged anion | 3 |
| Nonpolar Covalent Bond | Nuclei to shared electrons | 4 (Weakest) |
Intermolecular Forces
Intermolecular forces are weaker than intramolecular forces but influence physical properties like boiling point, melting point, and density.
Dipole-Dipole Interactions
These forces occur between the partially positive and partially negative parts of polar molecules, such as hydrogen chloride (HCl).
Hydrogen Bonding
A special type of dipole-dipole interaction occurring between a hydrogen atom bonded to oxygen, nitrogen, or fluorine and the partially negative end of another molecule.
London Dispersion Forces (Van der Waals Forces)
These weak forces exist between all molecules, regardless of polarity. The strength increases with the number of electrons in a molecule.
Concepts Related to Surface Tension
Cohesive Force
The force holding a liquid together, minimizing surface area. Strong cohesive forces maintain the liquid’s shape.
Adhesive Force
The force causing a liquid to spread out. Strong adhesive forces lead to liquid spreading.
Phase Transitions and Related Concepts
Enthalpy of Fusion (Latent Heat): The energy required to change a substance from solid to liquid at its melting point.
Vaporization: The conversion of a substance from liquid or solid to gas. Boiling involves vapor bubble formation within the liquid, while sublimation is the direct conversion from solid to vapor.
Capillary Action: The rise of liquid through a narrow tube.
Vapor Pressure: The pressure exerted by vapor molecules above a liquid.
Viscosity: A fluid’s resistance to flow.
Boiling Point: The temperature at which vapor pressure equals atmospheric pressure.
Unique Properties of Water
1. Attraction to Polar Molecules (Cohesion)
Water molecules attract each other through hydrogen bonds, creating surface tension.
2. High Specific Heat
Water requires a significant amount of energy to change its temperature.
3. Heat of Vaporization
Water requires a large amount of energy to change from liquid to gas.
Molar Heat of Vaporization of Water (Hv)
Equation: q = nHv, where q is the total heat, n is the number of moles, and Hv is the molar heat of vaporization.
4. Lower Density of Ice
Ice is less dense than water due to the arrangement of hydrogen bonds in its crystal structure.
5. High Polarity
Water’s polarity makes it a powerful solvent, dissolving polar substances like salt by forming hydration shells around ions.
Note: Polar substances dissolve polar substances.