This session we finished the compound naming rules and moved into polyatomic ions. Yana completed the third naming pattern — using prefixes like mono-, di- and tri- for compounds made of two non-metals, such as carbon dioxide and dinitrogen tetroxide — and we worked through why prefixes are used there but never for compounds containing a metal. We then introduced the seven polyatomic ions she needs to know (nitrate, sulfate, carbonate, hydroxide, phosphate, ammonium and hydrogencarbonate), including when brackets are needed in a formula and why calcium hydroxide is written Ca(OH)₂. We also went through her homework together and worked the percentage composition question from the worksheet as a pair.