2.4.2Foundations in Chemistry
Ionic Bonding and Structure
5 min read 4 parts Lesson 14 of 18
Section 1 of 4Ionic Bonding
Ionic compounds form between metals and non-metals, where electrons move from one atom to another.
Formation
- Electrons transfer from a metal atom to a non-metal atom, forming positive and negative ions with full outer shells.
The bond
- Ionic bonding is the strong electrostatic attraction between oppositely charged ions held in a lattice.
Dot-and-cross diagram
- Show the outer electrons of each atom, the transfer to the non-metal and the resulting charges in square brackets.
Example
- In sodium chloride, Na loses one electron to become Na⁺ and Cl gains one to become Cl⁻.
Section 2 of 4Giant Ionic Lattice and Properties
1
Ions are arranged in a regular repeating three-dimensional lattice in which each ion is surrounded by oppositely charged ions.
2
Melting requires a large amount of energy to overcome strong electrostatic forces in all directions, so melting points are high.
3
Solid ionic compounds do not conduct because the ions are fixed in position, but they conduct when molten or dissolved because ions can move.
4
A force shifts layers so that like charges line up, repel and split the crystal, so ionic solids are brittle.
5
Many ionic compounds dissolve in water, because polar water molecules are attracted to the ions and pull them out of the lattice.
Section 3 of 4Strength of Ionic Bonding
Strength of Ionic Bonding
Charge
- Higher charges give stronger attractions, so MgO (Mg²⁺ and O²⁻) has a much higher melting point than NaCl (Na⁺ and Cl⁻).
Ionic radius
- Smaller ions can get closer together, which produces a stronger attraction and a higher melting point.
Isoelectronic ions
- Ions with the same electron arrangement decrease in radius as the nuclear charge increases: O²⁻ > F⁻ > Na⁺ > Mg²⁺.
Down a group
- Ions with more shells are larger, so the attraction weakens and the melting point of the compounds falls.
| Property | Explanation |
|---|---|
| High melting point | Strong forces between ions in all directions |
| Brittle | Layers shift and like charges repel |
| Conducts when molten | Ions are free to move |
Section 4 of 4Exam Checklist & Tips
2.4.2 – Key Points for the Exam
- Ionic bond The electrostatic attraction between oppositely charged ions.
- Giant ionic lattice A regular three-dimensional arrangement of alternating positive and negative ions.
- Isoelectronic Having the same number of electrons and the same electron configuration.
- Brittle Tending to break or shatter when force is applied rather than bend.
Common Mistakes
- Saying ionic compounds contain molecules; they have a giant lattice and no discrete molecules.
- Stating that ions conduct in the solid state; they are fixed and cannot carry charge.
- Explaining melting in terms of breaking ionic bonds between pairs of atoms, rather than overcoming forces throughout the lattice.
- Describing the radius of a positive ion as larger than its atom, when it is smaller.