Define pure substances and elements
Pure substances:
A pure substance is a material that has a fixed chemical composition and distinct properties. It consists of only one type of particle, either atoms or molecules, and cannot be separated into simpler components by physical means. Pure substances can exist in various states of matter, such as solids, liquids, and gases. Examples of pure substances include water, oxygen gas, table salt (sodium chloride), and sugar (sucrose).
Elements:
An element is a pure substance that consists of only one type of atom. It is the simplest form of matter and cannot be decomposed into simpler substances by chemical reactions. Each element has its own unique properties and is represented by a chemical symbol, typically consisting of one or two letters. There are currently 118 known elements, and examples include oxygen (O), hydrogen (H), carbon (C), and gold (Au). Elements combine with each other in specific ratios to form compounds.