CHEMISTRY · Stage 9 · Chapter 10: Structure, Bonding, and Properties
Chemistry 10.4 Inside ionic compounds — Giant Ionic Lattices and Electrostatic Bonds
5 min read 6 parts Lesson 4 of 9
Lesson summary
10.4 Inside ionic compounds — Giant Ionic Lattices and Electrostatic Bonds — Alhussan International Academy — Chemistry (Stages 7–9) notes: Define ionic bonding, ionic compound and giant ionic structure, and explain the properties of ionic compounds using the giant ionic model.Io…
- Bonds act in all directions
- Brittleness
- Stronger attraction
- Insoluble compounds
- Sodium chloride
- Magnesium chloride
Section 1 of 6Ionic bonding
1Ionic bonding1 point
= the electrostatic attraction between positive and negative ions.
- A crystal of sodium chloride (NaCl) is made of millions of sodium ions and chloride ions held together this way.
2Formation2 points
- an ionic bond forms when a metal atom transfers outer electrons to a non-metal atom.
- Sodium (2,8,1) gives one electron to chlorine (2,8,7), forming Na+ and Cl-, each with a full outer shell.
3Ionic compound1 point
= a compound made up of positive and negative ions, and most compounds of a metal and a non-metal are ionic.
- Calcium oxide and nickel chloride are also ionic compounds.
Section 2 of 6Giant ionic structure
- Giant ionic structure = the three-dimensional pattern of oppositely charged ions held in the solid state.
- Lattice
- ions pack in a regular repeating pattern called a giant ionic lattice, with each ion surrounded by ions of the opposite charge.
- Bonds act in all directions
- the attraction acts throughout the crystal, and ionic compounds do not form single molecules.
- Formula
- it shows the simplest ratio of ions, for example NaCl is 1:1 and MgCl2 is 1:2.
Section 3 of 6Properties explained by the model
| Property | Explanation |
|---|---|
| High melting and boiling points | Many strong electrostatic attractions need a lot of energy to overcome |
| Hard but brittle | Layers shift so like charges line up and repel, and the crystal splits with straight edges |
| No conduction as a solid | Ions are fixed in place |
| Conducts when molten or dissolved | Ions are free to move and carry charge |
| Often soluble in water | Water molecules attract the ions and pull them apart |
- Brittleness
- if a crystal is dropped it breaks between one row of ions and another, leaving pieces with straight edges.
- Stronger attraction
- ions with double charges, as in magnesium oxide (Mg2+ and O2-), attract more strongly than in sodium chloride.
- Magnesium oxide melts at about 2850 °C compared with 801 °C for sodium chloride.
- Insoluble compounds
- some ionic compounds are insoluble because the attraction in the lattice is stronger than the attraction to water molecules.
Section 4 of 6Working out formulae
- Rule
- the total positive charge must equal the total negative charge.
- Examples
- Ca2+ and Cl- give CaCl2, and Mg2+ and O2- give MgO.
Section 5 of 6Dot-and-cross diagrams
- Draw the metal atom with its outer electrons and the non-metal atom with its outer electrons.
- Show the electron moving from the metal to the non-metal with an arrow.
- Draw each ion in square brackets with the charge at the top right outside the brackets.
- Sodium chloride
- sodium loses its outer shell and is shown as 2,8 with 1+, and chlorine has eight outer electrons and 1-.
- Magnesium chloride
- one magnesium atom transfers an electron to each of two chlorine atoms, giving MgCl2.
- Quick check
- the metal loses electrons, the non-metal gains them, and the charges balance in the formula.
Section 6 of 6Modelling ionic bonding
- Model = an idea that explains observations and helps make predictions, and the giant ionic structure is a model.
- Physical model
- Barney and Sarah used grapes to model a giant ionic structure of sodium chloride.
- Strength
- it shows the positions of the oppositely charged ions.
- Limitations
- it does not show that ions vibrate on the spot, how the attraction acts in all directions, or why ionic compounds are brittle.
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