How do I know when to use brackets in a compound with polyatomic ions?
Thanks drwls. :)
For example, sodium nitrite, I believe the answer is Na(NOsubscript2)
You don't need brackets for NaNO2 because it contains only one NO2 ion per molecule. If it were something like Ca(NO2)2, you would need two ions and would put the number of ions outside the bracket.
To determine when to use brackets in a compound with polyatomic ions, you need to understand the valence (or charge) of the ions involved. Here's a step-by-step process to help you:
1. Determine the valence of each individual ion in the compound. The valence is typically indicated by a superscript.
2. Identify the total charge of the polyatomic ion. This can be found by adding up the valences of all the atoms within the polyatomic ion.
3. Determine the number of each ion needed to balance the charges. If the charges are equal and opposite, you'll only need one of each ion. However, if the charges do not cancel out, you'll need to use brackets.
4. If brackets are necessary, enclose the polyatomic ion within brackets and write the subscript outside the bracket to indicate the number of ions needed. This is done to clarify the molecular formula and the number of ions present.
Let's take an example to better illustrate the concept. Consider the compound sodium sulfate (Na2SO4):
- Sodium (Na) has a valence of +1.
- Sulfate (SO4) has a valence of -2.
- The total charge of the sulfate ion is -2, which means it has two more negative charges than positive charges.
Since the charges do not cancel out, the brackets are used to indicate the presence of the sulfate ion. In this case, the subscript "2" is placed outside the brackets, indicating that two sulfate ions are needed. The final formula is Na2(SO4)2.
Remember, the use of brackets is necessary when multiple copies of a polyatomic ion are present within a compound and can help clarify the overall molecular formula by indicating the number of ions involved.