CHEM Chemical Bonding

4. Chemical Bonding

4.1 Why Do Atoms Combine?

  • Noble gases have full valence electron shells (duplet for Helium, octet for others), making them stable and unreactive.

  • Atoms combine to achieve noble gas electronic configurations through:

    • Loss of electrons

    • Gain of electrons

    • Sharing of electrons

4.2 What Is Ionic Bonding?

  • Ions are formed via loss or gain of electrons to achieve noble gas electronic configurations.

    • Positive ions (cations) are formed by losing electrons; metals tend to form positive ions.

      • Example: Na→Na++e−Na \rightarrow Na^+ + e^-

      • Example: Mg→Mg2++2e−Mg \rightarrow Mg^{2+} + 2e^-

    • Negative ions (anions) are formed by gaining electrons; non-metals tend to form negative ions.

      • Example: Cl+e−→Cl−Cl + e^- \rightarrow Cl^-

      • Example: O+2e−→O2−O + 2e^- \rightarrow O^{2-}

  • Ionic bond: Mutual electrostatic attraction between oppositely charged ions.

    • Example: Na+Cl→NaClNa + Cl \rightarrow NaCl

  • Ionic compounds:

    • Neutral substances formed from ions of opposite charges.

    • Ions arrange in a giant ionic crystal lattice.

4.3 What Is Covalent Bonding?

  • Covalent bond: Formed by sharing a pair of electrons; atoms achieve noble gas electronic configurations.

  • Valency: Number of electrons lost, gained, or shared to achieve a noble gas electronic configuration.

  • Single covalent bond: Sharing one pair of electrons (e.g., Cl2Cl_2).

  • Double covalent bond: Sharing two pairs of electrons (e.g., O2O_2).

  • Triple covalent bond: Sharing three pairs of electrons (e.g., N2N_2).

  • Covalent molecules:

    • Can be made from same or different elements (e.g., water (H2O)(H_2O)).