Chemical Bonds and Formulas

  • Chemical Bond

    • Definition: A chemical bond is the force of attraction between two atoms that overcomes the repulsion of their positively charged nuclei.
    • Purpose: Atoms bond to achieve a more stable electron configuration, often resembling a closed shell or noble gas configuration with valence electrons.

  • Valence Electrons

    • Only outer shell electrons are involved in bonding; inner core electrons do not participate due to their already stable configuration.
    • The octet rule suggests that atoms strive for eight valence electrons to achieve stability in their outer shells.

  • Types of Chemical Bonds

    • Ionic Bonds

    • Involve the transfer of electrons from one atom to another.

    • Form between metals and nonmetals or metalloids, creating charged ions.

    • Example: Sodium (Na) loses an electron to become Na⁺, and Sulfur (S) gains it to become S²⁻, resulting in the formation of Na₂S through ionic bonding.

    • Covalent Bonds

    • Involve sharing of electrons between atoms.

    • Typically form between nonmetals.

    • Example: Two hydrogen atoms (H) share their single electrons to create H₂, having a stable configuration resembling that of helium.

    • This sharing creates molecular orbitals, allowing each atom to attain a closed shell.

    • Metallic Bonds (not extensively covered)

    • Involve a sea of mobile electrons that can move freely from one metal atom to another.

  • Molecules and Crystalline Structures

    • Compounds formed can be discrete molecules (for covalent compounds) or extended arrays (for ionic compounds).
    • Example of covalent compound: Dry ice (solid CO₂) made of discrete carbon and oxygen molecules.
    • Example of ionic compound: Sodium chloride (NaCl) forms a large crystalline array due to the electrostatic attraction of positive and negative ions.

  • Representing Chemical Compounds

    • Space-Filling Model: Atoms represented as spheres, demonstrating the physical size and position of the atoms (e.g., water molecule H₂O).
    • Ball and Stick Model: Atoms represented as spheres connected by sticks to illustrate bonds between them.
    • Chemical Symbols and Formulas: Indicate creation of compounds and their proportions using chemical symbols and subscripts for atom counts.

  • Proportions and Chemical Formulas

    • Chemical formulas express composition and proportions of compounds.
    • Subscripts reflect the number of atoms (e.g., H₂O indicates 2 hydrogen atoms).
    • Parentheses indicate polyatomic groups.

  • Types of Chemical Formulas

    • Molecular Formula: Gives the exact number of atoms in a unit (e.g., C₆H₁₂O₆ for glucose).
    • Empirical Formula: Shows the simplest whole number ratio between elements (e.g., for hydrogen peroxide, its empirical formula is HO).
    • Structural Formula: Displays how atoms are bonded in a molecule, typically explored in further detail with tools like Lewis structures.

  • Summary of Fixed Proportions

    • Atoms combine in integer ratios to form compounds due to bonding.
    • Sodium chloride exists as a formula unit NaCl, indicating a 1:1 ratio of sodium to chlorine atoms in its crystal lattice, despite its larger composition in practice.

  • Conclusion

    • The understanding of chemical bonds is crucial as they dictate the structure and properties of matter, influencing how different substances interact and combine.