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Molecules, Atoms and Compounds Element A substance made up of only one kind of atom. Examples: Helium, Copper, and Gold Compound A substance made up of 2 or more DIFFERENT elements. Examples: Copper II oxide, salt (NaCl) and water (H2O) Element or Compound? Ca Na2O O2 Can be written with Chemical Symbols 1 or 2 letters used to represent an element st 1 letter is always capitalized If there is a 2nd letter it is lower case Chemical Formulas Subscripts indicate the number of atoms of the element. Example: AlCl3 1 aluminum atom 3 chlorine atoms Chemical formulas Practice: NH4Cl Mg(OH)2 Pb(NO3)2 Drawing Molecules represents a molecule made up of 2 different elements Another way to draw a molecule: Drawing Molecules Draw a pictorial representation of the following: Oxygen Calcium Ca O2 CaO Drawing Practice H2 O NH3 CCl4