Symbols Contain the symbol of the element, the mass number and the atomic number X Mass number Atomic # protons + # neutrons mass number # protons

F Symbols 19 9 Find the number of protons number of neutrons number of electrons Atomic number Mass number = 9 + F 19 9 = 10 = 9 = 9 http://ptcl.chem.ox.ac.uk/MSDS/glossary/corrosive.jpg = 19

Br Symbols 80 35 Find the number of protons number of neutrons number of electrons Atomic number Mass number = 35 = 45 Br 80 35 = 35 = 35 = 80 http://www.chem.purdue.edu/gchelp/liquids/bromine.gif

Na Symbols 23 11 Find the number of protons number of neutrons number of electrons Atomic number Mass number = 11 = 12 Na 23 = 11 = 11 11 http://www.webelements.com/webelements/elements/media/element-pics/Na.jpg = 23 Sodium atom

Na Symbols 23 11 Find the 1+ number of protons number of neutrons number of electrons Atomic number Mass number = 11 Na = 12 23 1+ = 10 11 = 11 = 23 Sodium ion

Symbols If an element has an atomic number of 23 and a mass number of 51 what is the number of protons number of neutrons number of electrons Complete symbol = 23 = 28 http://www.klenktools.com/Main/Images/All-combo-wrenches-sm.jpg = 23 V 51 23

Symbols If an element has 60 protons and 84 neutrons what is the Atomic number Mass number number of electrons Complete symbol = 60 = 144 = 60 http://www.stevespanglerscience.com/img/cache/02268c260f8fff6f7502dd93a20e39be/WMLN-100-260x250.jpg Nd 144 60

Symbols If a neutral atom of an element has 78 electrons and 117 neutrons what is the Atomic number Mass number number of protons Complete symbol = 78 = 195 = 78 Platinum is even more rare than gold. In fact, 50 tons of ore is required to produce just 50 grams of platinum. Platinum is a grayish-white metal that is malleable yet, like gold, is resistant to attack by air, moisture, and most solutions. Its melting point is even higher than gold, at just over 3,000°F. It ranks 72 in abundance among the elements. http://www.patbakersfinejewelry.com/graphics/platinum%20bar.jpg Pt 195 78

Mass Number Isotopes Ions Relative Atomic Mass Average Atomic Mass Masses of Atoms Mass Number Isotopes Ions Relative Atomic Mass Average Atomic Mass Law of definite proportions states that a chemical compound always contains the same proportion of elements by mass Percent composition — the percentage of each element present in a pure substance—is constant Calculation of mass percentage 1. Use atomic masses to calculate the molar mass of the compound 2. Divide the mass of each element by the molar mass of the compound and then multiply by 100% to obtain percentages 3. To find the mass of an element contained in a given mass of the compound, multiply the mass of the compound by the mass percentage of that element expressed as a decimal http://www.lakewoodconferences.com/direct/dbimage/50267226/Electronic_Scale.jpg Courtesy Christy Johannesson www.nisd.net/communicationsarts/pages/chem

Atomic Mass p+ n0 e– Ca 20 40 20 20 20 Ar 18 40 18 22 18 Br 35 80 35 45 35 Ca 40.08 20 Ar 39.948 18 Br 79.904 35

Bohr - Rutherford diagrams Putting all this together, we get B-R diagrams To draw them you must know the # of protons, neutrons, and electrons (2,8,8,2 filling order) Draw protons (p+), (n0) in circle (i.e. “nucleus”) Draw electrons around in shells He Li 3 p+ 4 n0 2e– 1e– Li shorthand 2 p+ 2 n0 3 p+ 4 n0 Draw Be, B, Al and shorthand diagrams for O, Na

Be B Al O Na 8 p+ 11 p+ 8 n° 12 n° 4 p+ 5 n° 5 p+ 6 n° 13 p+ 14 n° 2e– 8e– 1e– Na 8 p+ 8 n° 2e– 6e– O

Mass Number mass # = protons + neutrons always a whole number NOT on the Periodic Table! Neutron + Electrons Nucleus e- Proton e- e- Nucleus e- e- Carbon-12 Neutrons 6 Protons 6 Electrons 6 e-