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

3. Figure 02.16

5. Diatomic Gases

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

7. 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.  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.

9. 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.  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.

10. 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.  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.

11. 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.  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.

12.  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.  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. Atomic Mass

13. 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.

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

15. 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%).

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