Structure and Bonding
Ionic Bonding
Ionic bonding is the bonding in which there has been a transfer of electrons from one atom to another to produce ions. The substance is held together by strong electrostatic attractions between positive and negative ions. Ions are formed when it gains or loses electrons. Ones that gain forms negative ions, and ones that lose form positive ions.
- A positive ion is called a cation.
- A negative ion is called an anion.
You can find the charge of an ion by looking at the group it belongs to. If it belongs to groups 1-4, it has a charge of 1-4+ (they are positive), whereas, if it belongs to groups 5-0, it has a charge of 3—0. Below is a table containing charges of common ionic compounds and transition metals.
| Ion | Symbol | Charge |
| Silver | Ag | 1+ |
| Copper (I) | Cu | 1+ |
| Ammonium | NH4 | 1+ |
| Copper (II) | Cu | 2+ |
| Cobalt | Co | 2+ |
| Nickel | Ni | 2+ |
| Zinc | Zn | 2+ |
| Iron (II) | Fe | 2+ |
| Chromium | Cr | 3+ |
| Iron (III) | Fe | 3+ |
| Ion | Symbol | Charge |
| Hydroxide | OH | 1– |
| Nitrate | NO3 | 1– |
| Hydrogen Carbonate | HCO3 | 1– |
| Carbonate | CO3 | 2– |
| Sulphate | SO4 | 2– |
| Phosphide | P | 3– |
| Phosphate | PO4 | 3– |
| Nitride | N | 3– |
This is an example of a dot and cross diagram. The crosses represent the electrons on the sodium (anion) and the dots represent the electrons on the chlorine (cation). In a dot and cross diagram, you must use arrows to show which electrons are moved from the anion to the cation. On the final diagram, you mark the new electron(s) on the cation as a cross.
Boiling and Melting Points of Ionic Compounds
Ionic compounds have high boiling and melting points due to strong intermolecular forces between the atoms. This is because when the ions are formed during an ionic reaction, one of them would be positive, and one would be negative. Positive and negative attract and therefore, you get something like a strong magnet.
- As ionic charge increases, so does the melting/boiling points. Ions with 2+ and 2– would have stronger attraction because their charges a stronger, whereas, ions with 1+ and 1– would still have a strong attraction, but less stronger than 2+-
Structure of Ionic Compounds
An ionic crystal consists of giant three-dimensional lattices held together by strong electrostatic attractions between the positive and negative ions.
Structure of Sodium Chloride
This is the basic structure of a sodium chloride crystal. The green is the chloride and the blue is the sodium. Remember that each sodium is touched by six chlorides and each chloride is touched by six sodiums. Look at the middle atoms if unclear. Remember, this structure repeats itself over and over.
- Ionic bonds always produce giant structures.
- Ions form closely packed regular lattice arrangement.
- They have high melting/boiling points.
- The crystals tend to be brittle.
- Compounds tend to be soluble in water and insoluble in organic solvents.
Covalent Bonding
Covalent bonding is formed by sharing a pair of electrons between two atoms. This is so that both atoms can achieve a full outer shell. It is a strong attraction between the bonding pair of electrons and the nuclei of the atoms involved. Covalent compounds are only formed when the reactants are non-metals.
Diagrams YOU Need to Know…
