3.1.4 Periodicity - Properties of the elements of Period 3
Students should:
|
3.2 - Physical Properties
| Characteristic | Trend (left to right) | Reason |
| Atomic radius | decreases in size from left to right | increased attractive force (acting on the same energy shell) of the nucleus increases as the number of protons increases |
| Ionic radius | decreases across the period until formation of the negative ions then there is a sudden increase followed by a steady decrease to the end | In general as above. The sudden increase on formation of negative ions is due to the new (larger) outer shell |
| Electronegativity | Increases | More electron attracting power of the larger nuclear charge as we move to the right |
| Metallic character | Decreases - Na, Mg, Al metals; Si metalloid; P, S, Cl, Ar non-metals | Metallic character is a measure of the ease of loss of electrons from the outer shell. This decreases with increasing nuclear charge. |
| Melting point | Na 
Al steady increase |
Increasing availability of electrons in the metallic bonding associated with greater charge density of the metal ion |
| Si massive increase | Si giant macromolecular structure | |
| P large decrease | P4 molecules | |
| S small increase | S8 crown shaped molecules | |
| Cl
Ar decrease |
Cl2 molecules and Ar atoms |
