types of solids
There are 4 types of solids:
Metallic solids
Ionic solids
Covalent network solids
Molecular solids
A typical exam question will get you to compare two different solids so it is a good idea to learn their properties!
The above tabs give you a quick overview of the 4 types of solids - below, they are explained in more detail.
Metallic solids
Ionic solids
Covalent network solids
Molecular solids
A typical exam question will get you to compare two different solids so it is a good idea to learn their properties!
The above tabs give you a quick overview of the 4 types of solids - below, they are explained in more detail.
Metallic solids
They are made up of one type of metal atom held together with metallic bonds in a 3-D arrangement. The metallic bonds are an electrostatic attraction between the positive nuclei and the delocalised electrons.
This allows metals to be:
- Atoms have released their valence electrons to become positive ions. The positive nuclei are attracted to the delocalised electrons. The delocalised electrons are the valence electrons and do not belong to any particular atom therefore they can move throughout the lattice of positive ions.
This allows metals to be:
- Malleable (bent easily into shape - like a pot)
- Ductile (drawn out into thin wire - like the ones in your cell phone charges)
- Conductors of electricity due to the free moving electrons
- Conductors of heat due to the atoms vibrating and transferring energy
Ionic solids
Ionic solids contain positive and negative ions arranged in a 3-D lattice. Each positive cation ion is surrounded by negative anions and each anion is surrounded by cations. These ions are held together in a fixed position by strong electrostatic attractions known as ionic bonds. Because the ions are not free to move in their solid state, they can not conduct electricity. In their molten state however (when dissolved in water) the ions are free to move and can carry the charge. Therefore ionic solids can conduct electricity in their molten state.
Most ionic compounds are solid at room temperature and have high melting and boiling points because lots of energy is needed to break the strong ionic bonds.
Many dissolve in polar substances - click here for more info on polar substances.
To put it simply - water molecules have a slightly more positive end (the hydrogen's) and a slightly more negative end (the oxygen). The negative end of the water is attracted to the positive cations in the ionic solid and the positive end of the water is attracted to the negative anions. If the attraction between the water and the ions is greater then the electrostatic forces between the cations and anions, then the ionic solid will dissolve in water. If the electrostatic attraction between the cations and anions is greater, then the ionic solid will not dissolve. |
Covalent Network solids
Atoms that make up covalent network solids are arranged in regular lattice positions. The atoms are bonded to each other by strong covalent bonds and a lot of energy is required to separate the atoms from their lattice positions.
These covalent solids can exist in 2-D layers and 3-D networks
Two-dimensional layers
The example that is always looked at is graphite - this is your pencil lead!
Graphite is made up of carbon layers. Each carbon is covalently bonded to 3 others creating layers of hexagonal rings with delocalised electrons between the layers. The layers are attracted by weak intermolecular forces.
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Three-dimensional networks
The two common examples are diamond and silicon dioxide - these are 3-D networks held together by strong covalent bonds. In diamond, each carbon atom is covalently bonded to 4 others, therefore there are no free electrons and it will not conduct electricity. It is extremely strong and rigid and one of the hardest substances known. They have very high melting points to overcome these strong bonds.
Silicon dioxide is comprised of each silicon atom covalently bonded to 4 oxygen atoms. It also has an extremely high melting point and has no delocalised electrons therefore can not conduct electricity.
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Molecular Solids
These are made up of molecules! A molecule is formed when two or more atoms join together chemically.
These are usually made up of non-metal atoms - and are normally liquids and gases at room temperature but have cooled to become solids - hence classified as molecular solids.
These are usually made up of non-metal atoms - and are normally liquids and gases at room temperature but have cooled to become solids - hence classified as molecular solids.
There are two types of forces to be aware of:
Intramolecular forces: These forces are found within the molecule eg, bonding the oxygen atoms to the two hydrogen atoms. These are called covalent bonds and are very strong. Intermolecular forces: These are the forces between the different water molecules. eg, attracting one water molecule to another. These are much weaker and are the ones that are broken when water in it's liquid state is turned into it's gas state. |
- The weak intermolecular forces give rise to low melting and boiling points however, the larger the molecule, the more intermolecular forces, therefore the higher the melting point
- There are no free electrons or ions, therefore they do not conduct electricity
- Polar molecules will dissolve in polar solvents and non-polar molecules will dissolve in non-polar solvents. More on this here.