From "Smarter than a 5th Grader":
What is the simplest structural unit of an element or compound?
For covalent compounds, the answer would definitely be molecule. But I'm unclear as to how to show that the answer for ionic compounds or elements is "molecule".
For example, https://sites.google.com/site/rccchem2a/chapter-4-chemical-bonding-the-i states that ionic compounds: "Do not have molecules as basic structural unit. Instead extended array of positively and negatively charged particles called ions." Is the term 'structural unit' defined across Science as only for covalent compounds?