Final answer:
The claim that nitrides, phosphides, and arsenides always form ions with a 3- charge in binary salts is false. Elements like N, P, and As can form compounds with different charges depending on the metal they bind to and the type of bond (ionic or covalent) formed in the compound.
Step-by-step explanation:
The statement 'Nitrides, phosphides, and arsenides are always 3- in binary salts' is false. While it is often the case that these elements form ions with a 3- charge in their binary compound form with metals, there are exceptions based on the chemistry of the particular metal that they bind to.
For example, aluminum nitride is a binary ionic compound where aluminum has a +3 charge and nitride has a -3 charge, balanced out in the formula AlN. However, there are metals that form different types of bonds, including covalent bonds, and in such cases, the nitrogen, phosphorus, or arsenic could have an oxidation state other than -3. Also, compounds with metals in different oxidation states or in which these elements are bonded to non-metals may have different charges.
In the case of boron trihalides like BF3, boron uses sp2 hybridization for forming covalent bonds, and the resulting compound does not have a -3 charged boron, but it's instead neutral. Another example is when metals like lead (Pb) and tin (Sn), which can have an oxidation state of +4, form covalent halides rather than ionic compounds. For sodium nitride (Na3N), three sodium ions (Na+) balance out the single nitride ion (N3-) to form a neutral compound.