Warm-Up -Write the correct Nuclide Symbol for the following elements: *19 p+, 20 n *82 e-, 125n *Mass # 238, neutrons= 146

Isotopes Atoms of the same elements have the same number of protons HOWEVER there may be different numbers of neutrons and different mass numbers When an element’s atom has different numbers of neutrons, it is said to have isotopes

Hydrogen’s Three Isotopes Hydrogen has the following isotopes: Protium-a hydrogen atom with one proton and NO neutrons Deuterium-a hydrogen atom with one proton and only one neutron Tritium-a hydrogen atom with one proton and two neutrons

The atomic mass unit is based on the relation of standard carbon-12 Average Atomic Mass Atomic mass is the mass of an atom expressed in atomic mass units or amu The atomic mass unit is based on the relation of standard carbon-12 Begin 2nd here on 2/13/2012

Average Atomic Mass Continued Carbon-12 has a mass of 12.000 00 amu Example: If an atoms weighs half as much as carbon-12, its atomic mass will be 6.000 amu Begin 4th 10-13-2000 begin 5th, begin 7th

Example: If an atom weighs four times as much as carbon-12, it will have a mass of 48.000 00 amu

What is Atomic Mass? The atomic mass that is reported in the periodic table is a weighted average based on the relative abundance of each element

Relative abundance refers to how common the isotope occurs in nature Percent Abundance which refers to how many of each isotope are in every hundred

To Determine Avg. Atomic Mass 1) First convert relative abundance (%) to decimal equivalent 2) Multiply mass (in amu) by decimal equivalent 3) Add the numbers together 4) The sum (in amu) is the average atomic mass

For example, an element has two naturally occurring isotopes For example, an element has two naturally occurring isotopes. One isotope has a relative abundance of 19.91% and a mass of 10.012 amu. A second isotope has a relative abundance of 80.08% and a mass of 11.009 amu. Calculate the atomic mass

Example For example, an element has two naturally occurring isotopes. One isotope has a relative abundance of 92.58% and a mass of 7.02 amu. A second isotope has a relative abundance of 7.42% and a mass of 6.02 amu. Calculate the atomic mass

Additional Example Calculate the average atomic masses for the following: Isotope: Rel. Abund. Rel. Mass hydrogen-1 99.985% 1.008 hydrogen-2 0.015% 2.014 Begin 3rd 10-16-00, 4th 1.007 amu 1.0 amu (s.f.)

Practice Titanium has five common isotopes: If the abundance of Ti- 46 is 8.0%, Ti-47 is 7.8 %, Ti-48 is 73.4 %, Ti-49 is 5.5% and Ti- 50 is 5.3 %. What is the average atomic mass of titanium?

Isotope Rel. Abund. Actual Mass O-16 99.762 15.995 O-17 0.038 16.999 Determine Avg. Atomic Mass for oxygen: Isotope Rel. Abund. Actual Mass O-16 99.762 15.995 O-17 0.038 16.999 O-18 0.200 17.999

Magnesium consists of three naturally occurring isotopes Magnesium consists of three naturally occurring isotopes. The percent abundance of   these isotopes is as follows: 24Mg (78.70%), 25Mg (10.13%), and26Mg (11.7%). The average atomic mass of the three isotopes is 24.3050 amu. If the atomic mass of 25Mg is 24.98584 amu, and 26Mg is 25.98259 amu, calculate the actual atomic mass of 24Mg.   Answer : 23.985 AMU

Why is the mass in amu of a carbon‐12 atom reported as 12 Why is the mass in amu of a carbon‐12 atom reported as 12.011 in the periodic table of   the elements? The masses on the periodic table are the average mass of all isotopes and their abundances found in the universe. Although carbon‐12 weighs exactly 12 amu, the periodic table reports that the mass is 12.011 because we are taking into consideration the abundances and masses of the other two carbon isotopes (carbon‐13 and carbon‐ 14).

Copper used in electric wires comes in two flavors (isotopes): 63Cu and65Cu. 63Cu has an   atomic mass of 62.9298 amu and an abundance of 69.09%. The other isotope, 65Cu, has an   abundance of 30.91%. The average atomic mass between these two isotopes is 63.546 amu. Calculate the actual atomic mass of 65Cu.   Answer : Actual atomic mass of 65Cu = 64.9278 amu