Write the formulas for the following compounds: (a) copper(I) cyanide, (b) strontium chlorite, (c) perbromic acid, (d) hydroiodic acid, (e) disodium ammonium phosphate, (f) lead(II) carbonate, (g) tin(II) fluoride, (h) tetraphosphorus decasulfide, (i) mercury(II) oxide, (j) mercury(I) iodide, (k) selenium hexafluoride.

Understanding the difference between ionic and covalent compounds is fundamental in chemistry. Ionic compounds consist of a metal and a nonmetal (or a polyatomic ion), where the electrons are transferred from one atom to another, resulting in ions that attract each other to form a stable compound.

In contrast, covalent compounds involve nonmetals, where atoms share electrons to achieve a full outer electron shell. These shared electrons lead to the formation of bonds that keep the atoms together. For instance, in the step-by-step solution, 'tetraphosphorus decasulfide' and 'selenium hexafluoride' are covalent compounds where multiple nonmetals share electrons, as opposed to other listed compounds which are primarily ionic.

The process of writing chemical formulas requires an understanding of the charges of ions for ionic compounds and the number of atoms involved in covalent compounds. To correctly write chemical formulas for ionic compounds, you need to know the charges of the ions and use the crisscross method to ensure the overall charge of the compound is neutral.

The step-by-step solution demonstrates this approach, for example with copper(I) cyanide, where the charge of copper (Cu⁺) and cyanide (CN^-) are used to determine the formula CuCN. It's important to write the chemical symbols in the correct order: metal first, followed by the nonmetal or polyatomic ion.

A polyatomic ion is a group of atoms covalently bonded together that has an overall charge, acting as a single ion in chemical reactions. These ions are often part of ionic compounds and need to be understood when writing formulas.

Common examples include sulfate (SO₄^2-), nitrate (NO₃^-), and phosphate (PO₄^3-). When writing formulas involving these ions, parentheses may be needed if more than one of the same polyatomic ion is required, such as in strontium chlorite (Sr(ClO₂)₂) from the solution provided. It's important to memorize common polyatomic ions to improve efficiency in writing chemical formulas.

The naming of acids in chemistry follows certain rules that help in identifying the composition of the acid. Acids that don't contain oxygen are prefixed with 'hydro-' and end with '-ic'. For example, hydrochloric acid (HCl).

On the other hand, acids containing oxygen are named based on the polyatomic ion they contain. If the ion name ends in '-ate', the acid name will end in '-ic', and if the ion name ends in '-ite', the acid will end in '-ous'. The prefix 'per-' signifies that there's one more oxygen than the 'ate' form, while 'hypo-' indicates one less. The step-by-step solution provided uses this understanding to arrive at the formula for hydroiodic acid (HI) and perbromic acid (HBrO₄).