Properties of Solids
Introduced| English |
|---|
| molecular solids/məˈlekjʊlə ˈsɒlɪdz/ |
| ionic solids/aɪˈɒnɪk ˈsɒlɪdz/ |
| metallic solids/məˈtælɪk ˈsɒlɪdz/ |
| covalent-network solids/ˈkəʊvələnt ˈnetwɜːk ˈsɒlɪdz/ |
Four kinds of solid
- Diamond scratches glass; candle wax melts in your hand.
- Both are solids, yet they could not be more different.
- The difference is what holds their particles together.
- Four bonding types give four families of solid.
Ionic and molecular solids
- Ionic solids 离子固体 are ions in a lattice: high-melting and brittle.
- Molecular solids 分子固体 are molecules held by weak forces: low-melting and soft.
- Ice and sugar are molecular; salt is ionic.
Molecular solids tend to be soft with low melting points.
They are held by weak intermolecular forces, easily broken.
An ionic solid is hard but ____, shattering when a layer shifts.
Shifting a layer aligns like charges, which repel and crack it.
Network and metallic solids
- Covalent-network solids 共价网络固体 are one giant bonded lattice: very hard, very high-melting (diamond).
- Metallic solids 金属固体 are cations in an electron sea: they conduct and bend.
- Each type's properties follow directly from its bonding.
Diamond is very hard with a very high melting point. It is a...
One giant lattice of strong covalent bonds makes it hard and high-melting.
Match each solid to its type.
Salt = ionic, diamond = covalent network, copper = metallic.
Reading properties from bonding
- Strong, extended bonding gives a high melting point and hardness.
- Free-moving charges (ions when molten, electrons in metals) give conductivity.
- Weak forces give soft, low-melting molecular solids.
What kind of solid?
Match each solid's properties to its structure type.
Which type of solid conducts electricity in the solid state?
Only metals have mobile electrons in the solid; ionic needs melting first.
Why does diamond melt far hotter than dry ice (solid $\text{CO}_2$)?
- Diamond is a covalent network, so melting must break strong bonds.
- Dry ice is molecular, so melting only breaks weak forces between molecules.
Melting dry ice (solid $\text{CO}_2$) breaks...
It is a molecular solid, so only the weak intermolecular forces break.
Do not confuse the strong bonds inside a molecule with the weak forces between molecules -- melting a molecular solid breaks only the weak forces. Only metals conduct as solids; ionic solids conduct just when molten or dissolved; covalent networks and molecular solids usually do not conduct at all.
Four solids follow from four bondings: ionic solids (lattice of ions, brittle), molecular solids (weak forces, soft, low-melting), covalent-network solids (giant lattice, very hard), and metallic solids (electron sea, conducting). Strong extended bonding means high melting; free charges mean conduction.