Topic: Iosotopes and Avg. Atomic Mass  Do Now:. Dalton 1766 Remember #2…well Dalton was correct… 1)Atoms (tiny) 2)Atoms of same element are identical.

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Presentation transcript:

Topic: Iosotopes and Avg. Atomic Mass  Do Now:

Dalton 1766 Remember #2…well Dalton was correct… 1)Atoms (tiny) 2)Atoms of same element are identical * 3)Indestructible * 4)Combine in whole # ratio (H 2 O) 5)In chem rxn. are combined, separated, rearranged *turned out to not be entirely be true

These three hydrogens are found in nature  All H’s have 1 proton  H-1: mass # = = 0 neutrons 1-1 = 0 neutrons  H-2: mass # = = 1neutron 2-1 = 1neutron  H-3: mass # = = 2 neutrons 3-1 = 2 neutrons

Isotopes  atoms of same element with different # neutrons (mass # is different) different # neutrons (mass # is different) # protons stays same! (atomic # is same) # protons stays same! (atomic # is same)

Consider U-234, U-235, & U-238  What’s the atomic number of U?  How many protons in U?  How many neutrons in U-234?  How many neutrons in U-235?  How many neutrons in U-238?  How many electrons in U? – 92 = – 92 = – 92 =

Average Atomic Mass

  The atomic masses reported in the periodic table represent the weighted average of the masses of the naturally occurring isotopes of that element

Unit for Avg. Atomic Mass =  Amu (or regents says just u) – atomic mass unit Define as 1/12 the mass of a Carbon-12 atom Define as 1/12 the mass of a Carbon-12 atom

Avg. Atomic Mass of Chlorine (Cl has 2 isotopes) %Cl %Cl-35 % Abundance Mass(percent) + mass(percent) +…= avg. atomic mass 35(.75770) + 37(.24230) = amu

NOW YOU TRY Avg. Atomic Mass of Si 92.21% of Si has a mass of amu 4.70% of Si has a mass of amu 3.09% of Si has a mass of amu

Avg. Atomic Mass of Si X  amu X  amu X  amu X  amu X  amu X  amu amu amu