Overview
This lecture explains ionic bonding, the formation of ions, and how to represent these processes using dot and cross diagrams, with examples such as sodium chloride and magnesium chloride.
Formation of Ions
- Ions are formed when atoms gain or lose electrons to achieve a full outer shell.
- Sodium loses one electron to become a Na⁺ ion.
- Chlorine gains one electron to become a Cl⁻ ion.
- Ionic equations show the loss or gain of electrons during ion formation.
Ionic Bonding
- An electron transfers from a metal atom (e.g., sodium) to a non-metal atom (e.g., chlorine).
- Both atoms become oppositely charged ions with full outer shells.
- Opposite charges attract each other by strong electrostatic forces called ionic bonds.
- Ionic bonds are similar in strength to covalent bonds.
Dot and Cross Diagrams
- Dot and cross diagrams represent the transfer of electrons with dots for one atom’s electrons and crosses for the other’s.
- Arrows show the movement of electrons between atoms.
- Draw all electron shells unless instructed to show only the outer shell.
- Square brackets indicate ions, and their charges are shown in the top right corner.
Example: Magnesium Chloride (MgCl₂)
- Magnesium has two outer electrons; each chlorine has seven outer electrons.
- Magnesium donates one electron to each of two chlorine atoms.
- Final ions: one Mg²⁺ ion and two Cl⁻ ions.
- Arrange ions as they would be in a compound, with chlorides on either side of magnesium.
Key Terms & Definitions
- Ion — An atom or molecule with a net electric charge due to loss or gain of electrons.
- Ionic bond — A strong electrostatic force between oppositely charged ions.
- Dot and cross diagram — A visual representation showing electron transfers in bonding, using dots and crosses for different atoms' electrons.
Action Items / Next Steps
- Practice drawing dot and cross diagrams, focusing on both full and outer shell versions.
- Review ionic bonding processes and be prepared to replicate these examples in exams.