2.2.2The Particulate Nature of Matter
Ionic Bonds and Lattice Structure — Combined Science 0653 - Chemistry Revision Notes & Topical Questions
5 min read 6 parts Lesson 6 of 13 Unit quiz
Section 1 of 6Forming an ionic compound
1
Ionic compounds form when metal atoms react with non-metal atoms.
2
The metal atom loses its outer electrons and becomes a positive ion.
3
The non-metal atom gains those electrons and becomes a negative ion.
4
Each ion now has a full outer shell, and the opposite charges attract strongly. This is the ionic bond.
5
The compound has no overall charge, because the total positive charge equals the total negative charge.
Section 2 of 6Worked example: magnesium oxide
1Magnesium atom
- Magnesium atom Magnesium is in Group II and has two outer electrons, configuration 2,8,2.
2Oxygen atom
- Oxygen atom Oxygen is in Group VI and has six outer electrons, configuration 2,6, so it needs two more.
3Transfer
- Transfer Two electrons move from magnesium to oxygen.
4Ions formed
- Ions formed Mg2+ (2,8) and O2- (2,8) are formed. The formula is MgO, with no overall charge.
Section 3 of 6Drawing the dot-and-cross diagram
Outer shell only
- Outer shell only Show only the outer shell of each ion.
- Use dots for electrons from one atom and crosses for the other.
Brackets and charges
- Brackets and charges Put square brackets round each ion and write its charge at the top right.
Balance the charges
- Balance the charges If the charges do not cancel, draw more ions.
- For example, magnesium chloride needs two chloride ions for each magnesium ion.
Section 4 of 6Giant lattice structure (Extended)
Ionic lattice
Regular arrangement
- Regular arrangement The lattice is a three-dimensional pattern in which the particles are arranged in an ordered, repeating way.
Alternating ions
- Alternating ions Positive and negative ions alternate, so each ion is surrounded by ions of the opposite charge.
Giant structure
- Giant structure The structure carries on in all directions, so there are no separate molecules.
- Sodium chloride (NaCl) is a typical example.
Strong attractions
- Strong attractions Many strong electrostatic attractions act throughout the lattice, which is why ionic compounds have high melting points.
Section 5 of 6Key terms
| Term | Meaning |
|---|---|
| Ion | An atom or group of atoms with a positive or negative charge because it has lost or gained electrons. |
| Ionic bond | The strong electrostatic attraction between oppositely charged ions. |
| Lattice | A regular, repeating three-dimensional arrangement of particles. |
| Dot-and-cross diagram | A diagram showing the outer electrons of atoms or ions using dots and crosses to show where they came from. |
| Giant structure | A structure with a huge number of particles bonded together in a continuous network. |
Section 6 of 6Exam technique
1
Drawing shared electron pairs in an ionic compound. Ionic bonding involves transfer, not sharing.
2
Leaving out square brackets or charges on the ions in a dot-and-cross diagram.
3
Giving a compound an overall charge. Ionic compounds are neutral overall.
4
Describing sodium chloride as made of molecules. It is a giant lattice of ions.
Last updated: