Properties of Solids
Introduced| English | Meaning |
|---|---|
| molecular solids/məˈlekjʊlə ˈsɒlɪdz/ | molecular solids |
| ionic solids/aɪˈɒnɪk ˈsɒlɪdz/ | ionic solids |
| metallic solids/məˈtælɪk ˈsɒlɪdz/ | metallic solids |
| covalent-network solids/ˈkəʊvələnt ˈnetwɜːk ˈsɒlɪdz/ | covalent-network solids |
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.
The four solid structures: giant ionic, simple molecular, giant covalent, and metallic
Molecular solids tend to be very hard with high melting points.
Difficulty 1/5 · 100 coins + a small bonus on first completion today
False. Molecular solids are held by weak intermolecular forces, so they tend to be soft with low melting points. Hard, high-melting solids are usually covalent network or ionic.
An ionic solid is hard but ____, shattering when a layer shifts.
Difficulty 1/5 · 100 coins + a small bonus on first completion today
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...
Difficulty 1/5 · 100 coins + a small bonus on first completion today
One giant lattice of strong covalent bonds makes it hard and high-melting.
Match each solid to its type.
Difficulty 2/5 · 140 coins + a small bonus on first completion today
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?
Difficulty 1/5 · 100 coins + a small bonus on first completion today
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...
Difficulty 1/5 · 100 coins + a small bonus on first completion today
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.