One mole of any substance is 6.02 x particles of that substance (this is named in honor of Amadeo Avogadro, thus is called “Avogadro’s number”) You’ll probably want to memorize this number! Converting from particles to moles

Representative particles For an element, the representative particle is an atom For an ionic compound, the representative particle is a formula unit (sometimes we also look at the number of ions – then we must look at the number of ions in the formula unit) For a molecular compound, the representative particle is a molecule

How do you know what type of substance is present? It’s easy to recognize an element – a substance that isn’t combined with anything else If you see just an element symbol - the representative particle is an atom

Diatomic elements 7 elements are diatomic (2 atoms bonded together) when they are NOT combined in a compound with other elements Memorize these seven elements! Their representative particle is a molecule, NOT an atom. O 2 oxygen H 2 hydrogen N 2 nitrogen F 2 fluorine Cl 2 chlorine Br 2 bromine I 2 iodine

Recognizing Ionic or Molecular Compounds It’s easy to recognize an ionic compound – two (or more) ions are chemically bonded together look for metals that are combined with nonmetals. Find the stairstep line on your periodic table – metals are to the left of the line nonmetals are to the right A compound that is NOT ionic is molecular

Examples How many moles of Fe are present in 2.49 x atoms of Fe? (how do we know the particles are atoms?) 1 mole Fe = 6.02 x atoms 2.49 x atoms x 1 mole Fe = 4.14 mol Fe 6.02 x atoms

Example How many moles of water are present in 3.55 x molecules of H 2 O? (how do we know the particles are molecules?) 3.55 x molecules x 1 mole H 2 O = mol H 2 O 6.02 x molecules

Example How many moles of KCl are present if you have 3.04 x formula units of KCl? (remember, the formula unit KCl is made up of potassium ions and chloride ions) 3.04 x formula units x 1 mole KCl = 5.05 mol KCl 6.02 x formula units

Example How many moles are present in 3.25 x molecules of H 2 ? (how do we know they are molecules?) 3.25 x molecules x 1 mole H 2 = mol H x molecules