CHEMISTRY · Stage 9 · Chapter 10: Structure, Bonding, and Properties
Chemistry 10.7 More about structures — Bonding, Melting Points and Conductivity
5 min read 7 parts Lesson 7 of 9
Lesson summary
10.7 More about structures — Bonding, Melting Points and Conductivity — Alhussan International Academy — Chemistry (Stages 7–9) notes: Describe giant metallic structures, summarise the four types of structure and use data to identify bonding and structure.Alloys — steel is mainly…
- Metallic bonding
- High strength and melting points
- Steel in buildings
- Explanation pattern
- Comparisons
- Non-metals
Section 1 of 7Giant metallic structures
- Alloys
- steel is mainly iron with small amounts of other elements, and metal elements and alloys are strong because of their structure.
- Particles
- metal atoms lose their outer electrons to achieve a stable electron configuration,
- so a metal contains two types of particle: positive ions and negative electrons.
- The ions are in fixed positions in layers.
- The electrons move around between the ions.
- Metallic bonding = the electrostatic attraction between positive metal ions and moving negative electrons, which holds the metal together.
- Giant metallic structure = the three-dimensional pattern of positive metal ions held together by moving electrons.
Section 2 of 7Properties of metals
- High strength and melting points
- the strong electrostatic attraction between fixed positive ions and moving electrons needs a lot of energy to overcome.
- Conductivity
- the moving electrons allow metals to conduct electricity, even as solids.
- Steel in buildings
- steel bars embedded in concrete give the strength needed in a tall building such as the Burj Khalifa in Dubai.
Section 3 of 7Four types of structure
| Structure | Particles | Elements or compounds | Typical state at 20 °C | Examples |
|---|---|---|---|---|
| Ionic (giant) | Positive and negative ions | Compounds | Solid | Sodium chloride |
| Metallic (giant) | Positive ions and negative electrons | Elements | Solid | Gold |
| Giant covalent | Atoms joined by covalent bonds | Elements and compounds | Solid | Diamond, silicon dioxide |
| Simple covalent | Molecules joined by covalent bonds | Elements and compounds | Liquid or gas | Hydrogen, carbon dioxide |
Section 4 of 7Evidence for each structure
| Property | Ionic lattice | Simple molecular | Giant covalent | Metallic |
|---|---|---|---|---|
| Melting point | High | Low | Very high | Usually high |
| Conducts as solid | No | No | No (graphite yes) | Yes |
| Conducts when molten | Yes | No | No | Yes |
| Soluble in water | Often | Rarely | No | No |
Section 5 of 7Why bonding determines the property
1Melting point4 points
- it depends on how much energy is needed to overcome the attractions between particles.
- In ionic compounds there are strong electrostatic forces in all directions.
- In simple molecular substances only the weak forces between molecules are overcome.
- In giant covalent structures many strong covalent bonds must be broken.
2Conductivity3 points
- it needs charged particles that can move.
- Ions carry charge when molten or dissolved.
- Delocalised electrons carry charge in metals and graphite.
Section 6 of 7Identifying an unknown substance
- Check the melting point: a low value suggests simple molecules.
- If the melting point is high, check whether the solid conducts: if it does, it is a metal (or graphite).
- If it does not conduct as a solid but conducts when molten or in solution, it is ionic.
- If it never conducts and has a very high melting point, it is giant covalent.
- Explanation pattern
- state the structure, describe the particles and forces, and link them to the property.
- Comparisons
- magnesium oxide melts higher than sodium chloride because of higher charges and stronger attraction.
- Diamond is harder than graphite because of a rigid network versus sliding layers.
Section 7 of 7Structure and the periodic table
- Metals
- all metal elements have giant metallic structures.
- Non-metals
- most exist as molecules, and a few have giant covalent structures.
- Noble gases
- they exist as single atoms.
- No ionic elements
- no element has a giant ionic structure, because ionic structures need two different types of ion, so they occur only in compounds.
- Prediction
- knowing the structure of an element helps predict its properties.
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