IB MYP 4-5 Chemistry -Ionic, covalent, and metallic bonding- Study Notes - New Syllabus

 Chemical Bonding – Ionic, Covalent, and Metallic Bonds

Chemical bonding is the process by which atoms combine to form molecules or compounds. Atoms bond together to achieve stability — usually by attaining a full outer electron shell (the octet rule).

Why Atoms Form Bonds:

• To achieve a stable electronic configuration (like noble gases).
• To lower their potential energy by sharing or transferring electrons.
• To form substances with new chemical properties.

Types of Chemical Bonds

• Ionic bond — transfer of electrons between a metal and a non-metal.
• Covalent bond — sharing of electrons between two non-metals.
• Metallic bond — attraction between positive metal ions and delocalized electrons.

Ionic Bond

 An ionic bond is formed when one or more electrons are transferred from a metal atom to a non-metal atom, resulting in oppositely charged ions that attract each other electrostatically.

\( \mathrm{Metal\ (loses\ e^-)\ \rightarrow\ Cation} \)

\( \mathrm{Non\text{-}metal\ (gains\ e^-)\ \rightarrow\ Anion} \)

Example: Formation of Sodium Chloride (\( \mathrm{NaCl} \))

• \( \mathrm{Na} \) (2,8,1) → loses 1 electron → \( \mathrm{Na^+} \)
• \( \mathrm{Cl} \) (2,8,7) → gains 1 electron → \( \mathrm{Cl^-} \)
• Opposite charges attract → \( \mathrm{Na^+Cl^-} \)

Properties of Ionic Compounds:

• Form crystal lattices with strong electrostatic forces.
• High melting and boiling points.
• Conduct electricity only when molten or dissolved (ions free to move).
• Brittle (break under stress due to repulsion of like charges).
• Usually soluble in water.

Exceptions:

• Some ionic compounds (e.g., \( \mathrm{CaCO_3} \)) are sparingly soluble.
• Transition metals can form partially covalent ionic compounds due to polarization (e.g., \( \mathrm{CuCl_2} \)).

Covalent Bond

 A covalent bond forms when two non-metal atoms share one or more pairs of electrons to achieve full outer shells.

\( \mathrm{A + B \rightarrow A{:}B} \)

Example: Formation of Water (\( \mathrm{H_2O} \))

• Each hydrogen shares 1 electron with oxygen.
• Oxygen shares 2 electrons (one with each H) → total 8 electrons around oxygen.
• Molecule formed: \( \mathrm{H–O–H} \)

Types of Covalent Bonds:

• Single bond: One shared pair (e.g., \( \mathrm{H_2} \), \( \mathrm{Cl_2} \))
• Double bond: Two shared pairs (e.g., \( \mathrm{O_2} \))
• Triple bond: Three shared pairs (e.g., \( \mathrm{N_2} \))

Properties of Covalent Compounds:

• Low melting and boiling points (weak intermolecular forces).
• Do not conduct electricity (no free ions).
• Usually gases or liquids at room temperature.
• Insoluble in water but soluble in organic solvents.

Exceptions to Covalent Rules:

• \( \mathrm{NH_4^+} \) (ammonium ion) has coordinate (dative) covalent bonds.
• \( \mathrm{BF_3} \) has incomplete octet (only 6 electrons around B).
• \( \mathrm{SF_6} \) has expanded octet (12 electrons around S).

Metallic Bond

 A metallic bond is the force of attraction between positive metal ions and a “sea” of delocalized electrons that move freely throughout the metal lattice.

Model: Atoms release outer electrons → form cations → free electrons move → attraction between cations and electrons holds metal together.

Properties of Metallic Substances:

• Good conductors of heat and electricity (due to mobile electrons).
• Malleable and ductile (layers of atoms slide easily).
• High melting and boiling points (strong bonds).
• Show metallic lustre (reflect light due to electrons).
• Form alloys (mixtures of metals improve strength or resistance).

Examples:

• Copper (Cu) → good conductor used in wiring.
• Iron (Fe) → strong, used in structures.
• Alloy example: Brass = Copper + Zinc.

Comparison of Bond Types