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Periodic table

Periodic table. Groups – Columns down Alkali Metals Alkaline Earth Metals Halogens Noble gases Periods – Rows across Lanthanides Actinides. Figure 02.16. Diatomic Gases.

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Periodic table

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  1. Periodic table Groups – Columns down Alkali Metals Alkaline Earth Metals Halogens Noble gases Periods – Rows across Lanthanides Actinides

  2. Figure 02.16

  3. Diatomic Gases

  4. Element Symbols Atomic Number=number of protons (+)the Z numberAtomic Mass=number of protons and neutrons (+/-) the A number

  5. Isotopes • There are three different types of oxygen atoms shown above. • All have same # protons, but diff # neutrons, and diff mass # • Chemically alike because have identical # protons and electrons, which are subatomic particles responsible for chemical behavior.

  6. Symbol Practice Problems • Write the symbol for each of the three isotopes for oxygen (oxygen-16, oxygen-17 and oxygen-18) including atomic # and mass # • Three isotopes of chromium are Cr-50, Cr-52, and Cr-53. How many neutrons are in each isotope? Atomic number of Cr is 24.

  7. Atomic Mass (amu) • In nature, most elements occur as mixture of one or two isotopes. • Each isotope has a fixed mass and natural percent abundance. • Consider three isotopes of Hydrogen • Hydrogen 1 (99.985%) • Hydrogen 2 and 3 present in trace amounts. • Look at atomic mass of H on periodic table (1.0079) • This is very close to the mass of hydrogen-1 (1.0078). • The slight difference takes into account the larger masses, but the smaller amounts of the other two isotopes of hydrogen.

  8. Atomic Mass • Atomic mass of an element is a weighted average mass of the atoms in a naturally occurring sample of an element. • Weighted average mass accounts for both mass and relative abundance of isotopes.

  9. Atomic Mass • You can calculate the atomic mass of an element if you are given: • The number of isotopes • The mass of each isotope • The percent abundance of each isotope. • To calculate the atomic mass, multiply the mass of each isotope by its natural abundance (in decimal form) then add the products.

  10. Example - Average Atomic Mass • Copper has two stable isotopes: carbon-12 has abundance of 98.89% and carbon-13 has natural abundance of 1.11%. The mass of Carbon-12 is 12.00 amu and the mass of Carbon-13 is 13.003 amu. Calculate atomic mass of Carbon.

  11. Answer • Atomic mass of carbon = (12.00amu X .9889) + (13.003 X 0.0111) = 12.011 amu

  12. Example • Calculate the atomic mass of bromine. The two isotopes of bromine have atomic masses and relative abundance of 78.92 amu (50.69%) and 80.92 amu (49.31%).

  13. Answer • Atomic mass of Bromine: (78.92 amu X .5069) + (80.92 amu X .4931) = 79.91 amu • Homework: Complete isotopes worksheet

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