1.4 Isotopes, Radioisotopes and Atomic Mass

Recall Standard Notation for an Element

Isotopes Frederick Soddy was the first to propose the theory of isotopes Different isotopes of a given element have the same atomic number but different mass numbers since they have different numbers of neutrons Chemical properties of the different isotopes of an element are identical, but they will often have great differences in nuclear stability Some elements consist of one isotope but many consist of a mixture of isotopes

as a result of isotopes, unified atomic mass units (amu) are used to calculate the mass number of elements only 80 elements have any stable isotopes Isotopic Abundance is the percentage of an isotope in a sample A Mass Spectrometer is a tool used to distinguish isotopes and their abundance in a sample

Mass Spectrometer

Radioisotopes some elements have isotopes that are unstable and as they decay they emit radiation it can be a quick or slow process depending on the isotope the radiation they emit can be harmless or lethal there are 3 main types of nuclear radiation: alpha particles, beta particles and gamma rays

Radioactive decay and Half-life The concept of radioactive decay was discovered by a Canadian scientist- Harriet Brooks (1876-1933) Half-life is the amount of time required for ½ of the nuclei in a radio active sample to decay Half lives of radioisotopes vary considerably from element to element

Ex: a by product of forming uranium for nuclear reactors is radium-226 which has a half-life of 1 600 years or annum (a). If your sample is initially 25g, how much would remain after: a) one half-life b)five half-lives

Uses of Radioisotopes Smoke detectors- Americium-241 Agricultural Applications- phosphorus-32 Food Irradiation - cobalt-60 Archaeological Dating carbon -14 Medical- various tracers that are given and help image various tissues or bone in a scan

Finding the Mass given Isotopic Abundance Silicon has three isotopes Si-28, Si-29, and Si 30. In a sample 92.8% of the atoms are Si-28 with a mass of 28.001, 4.70% of the atoms are Si-29 with a mass of 29.750 and 3.02% of the atoms are Si-30 with a mass of 30.005. Calculate the average atomic mass of silicon.