SUMMARY OF MODULE 2
There are three main types of chemical bonds:
- Ionic bonding
- Convalent bonding
- Metallic bonding
Ionic bonding -
The electrostatic attraction between oppositely charged ions.
Ionic compounds are only formed of metals bonded with non-metals
They are made of ions (atoms which have donated or gained an electron/s giving them a positive or negative charge) for example:
Many of these positive and negative ions strongly attract one another to form a giant crystal lattice structure.
These strong intramolecular bonds and the giant structure determine the properties of ionic compounds.
PROPERTIES OF AN IONIC COMPOUND
- High melting and boiling points:
This is because there are strong ionic bonds between the ions. These strong electrostatic forces between the ions requires alot of energy to overcome.
- High conductivity (ONLY IN LIQUID FORM)
Solid ionic structures are not able to conduct electricity as their charged ions are fixed in place, however if you dissolve or melt the structure into it's liquid form it is able to conduct electricity as the ions are mobile and can carry the charge.
- Soluable in polar solvents
The ionic lattices can be dissolved in polar solvents such as H2O as the polar molecule as the slightly positive hydrogen parts of the water molecules attract the negative ions from the structure and the same goes for the slightly negative oxygen part of the water with the positive ions - this pulls the ions apart from the lattice and to dissolve into the water.
Convalent bonding -
Where atoms share outer electrons to sustain a full outer shell. Convalent bonding only happens between non-metals and can either form a giant or simple structure, this structure determines the properties of the molecule.
Molecules with a simple convalent structure:
These are substances such as H2O and CO2 which are made of simple molecules.
These molecules have strong intramolecular bonds holding the atoms together but weak intermolecular forces, altering it's properties.
- Low melting and boiling points
Simple molecular structures have very weak intermolecular bonds which require little energy to overcome
- No electrical conductivity
This is because the molecules are not charged and therefore cannot carry an electric current
- Soluable in non-polar solvents
This is because Van der waals forces begin to form between the solvent and the molecules which weaken the lattice structure, causing it to dissolve.
Giant convalent strucures (Macromolecules)
These form when many of the same atoms are convalently joined to make giant structures rather than small groups. For example:
Diamond (formed of carbon atoms each bonded to four other carbon atoms)
- High melting and boiling points
Strong convalent bonds hold the structure together, therefore alot of energy is required to overcome them
- Insoluable in polar and non-polar…