Chemguide: Support for CIE A level Chemistry
Learning outcome 9.2(e) and part of 9.2(f)
This statement - 9.2(e) - deals with the reactions of the chlorides of the elements in Period 3 with water. 9.2(f) is involved in the explanation for this.
Before you go on, you should find and read the statements in your copy of the syllabus.
Remember that we are only dealing with the chlorides:
NaCl, MgCl2, AlCl3 / Al2Cl6, SiCl4, and PCl5.
The reactions between these chlorides and water are found on the page period 3 chlorides. That page contains a lot of information, and it is important that you concentrate on what you need to know.
Remember that you don't need to know about phosphorus(III) chloride, or the chlorides of sulphur.
What you need to get from the page
What follows is just a summary of the important things. It isn't a substitute for reading the page.
The structure of the chlorides
You need to know that:
You need to understand that the reason for this is that the electronegativity difference between the other element and chlorine falls as you go across the period. Sodium has a low electronegativity and that means that there is enough electronegativity difference between sodium and chlorine to get an ionic bond.
As you go across the period, the electronegativity of the elements increases, and by the time you get to aluminium, the electronegativity difference between aluminium and chlorine is barely enough to get ions formed, and aluminium chloride often exists as covalent molecules.
After aluminium, there isn't enough electronegativity difference to get ions, and so the compounds are all covalent.
Note: If you aren't confident about electronegativity follow this link to find out more about it.
The reactions with water
You should know that:
© Jim Clark 2010 (last modified January 2018)