Chemical Bonding

Chemical bonding is the process by which atoms combine to form compounds by either transferring or sharing electrons to achieve full outer electron shells, resulting in more stable arrangements.

Ionic Bonding

Ionic bonding occurs when atoms transfer electrons to achieve full outer shells, forming ions. Metals tend to lose electrons to become positively charged ions (cations), while non-metals gain electrons to become negatively charged ions (anions).

The oppositely charged ions are held together by strong electrostatic forces of attraction, creating an ionic bond.

Example: Sodium (Na) has 1 electron in its outer shell, and chlorine (Cl) has 7 electrons in its outer shell. Sodium transfers its 1 electron to chlorine. Sodium becomes Na⁺ and chlorine becomes Cl⁻. These ions attract each other to form sodium chloride (NaCl).

Ionic compounds form giant lattice structures where each ion is surrounded by ions of opposite charge. This arrangement maximises attraction and minimises repulsion, making ionic compounds very stable.

Properties of ionic compounds include:

• High melting and boiling points due to strong ionic bonds requiring lots of energy to break.
• Usually soluble in water because water molecules can separate the ions.
• Conduct electricity when molten or dissolved in water, as ions are free to move and carry charge.
• Do not conduct electricity when solid because ions are fixed in place.

Covalent Bonding

Covalent bonding happens when atoms share pairs of electrons to fill their outer shells. This usually occurs between non-metal atoms.

Each shared pair of electrons forms a covalent bond, holding the atoms together.

Simple molecular substances consist of small molecules held together by covalent bonds. Examples include water (H₂O), oxygen (O₂), and methane (CH₄).

Properties of simple covalent compounds:

• Low melting and boiling points because the forces between molecules (intermolecular forces) are weak and easy to overcome.
• Do not conduct electricity as there are no free charged particles.
• Often insoluble in water but soluble in non-polar solvents.

Example: In a hydrogen molecule (H₂), each hydrogen atom shares its one electron with the other, forming a single covalent bond. This gives both atoms a full outer shell of two electrons.

Metallic Bonding

Metallic bonding occurs between metal atoms. Metals have atoms arranged in a regular lattice structure, where outer electrons become delocalised (free to move throughout the structure).

The positive metal ions are held together by the strong electrostatic attraction to the sea of delocalised electrons. This is the metallic bond.

Properties of metals due to metallic bonding include:

• High melting and boiling points because metallic bonds are strong and require a lot of energy to break.
• Good electrical conductivity as delocalised electrons can move and carry charge.
• Good thermal conductivity as delocalised electrons transfer energy quickly.
• Malleability and ductility because metal ions can slide over each other without breaking the metallic bond.

Example: In copper metal, each copper atom contributes its outer electrons to a sea of delocalised electrons that move freely, holding the metal ions together in a lattice.

Dot and Cross Diagrams

Dot and cross diagrams are used to represent bonding by showing the outer electrons of atoms. They help visualise how electrons are transferred or shared in ionic and covalent bonds.

In ionic bonding diagrams:

• Electrons transferred from metal atoms (dots) to non-metal atoms (crosses).
• Resulting ions are shown with full outer shells and charges.

In covalent bonding diagrams:

• Shared pairs of electrons are shown between atoms.
• Electrons from each atom are represented by dots or crosses to distinguish their origin.

These diagrams make it easier to see how atoms achieve full outer shells through bonding.

Example: In the dot and cross diagram for hydrogen chloride (HCl), the hydrogen atom shares one electron (dot) with the chlorine atom’s electron (cross), forming a single covalent bond.

Inline Example: For instance, chlorine (Cl) has 7 electrons in its outer shell and needs 1 more to be full. When it bonds covalently with hydrogen (H), which has 1 electron, they share a pair of electrons to form HCl.