Download PowerPoint - Significant Digits in Calculations, Isotopes

Isotopic Abundance
Reminder: bring a
calculator to class
Isotopes & Radioisotopes
• Isotopes have same number of protons
(atomic #) and different numbers of
neutrons and therefore different masses
• Isotopic abundance is the percentage of a
given isotope in a sample of an element.
• Mass spectrometer is used to determine the
mass and abundance of isotopes
• Radioisotopes are isotopes that have
unstable nucleus and undergo radioactive
decay.
• Radioactive decay is the spontaneous
disintegration of unstable isotopes to emit
nuclear radiation such as alpha particle, beta
particle and gamma ray
Nuclear radiation
• Particles emitted from nucleus of
radioisotopes
• Alpha particle – a positively charged
particle with the same structure as the
nucleus of a helium atom
• Beta particle – a negatively charged particle
identical to an electron
• Gamma ray – a high-energy
electromagnetic radiation
Isotopic abundance
• Let’s consider the following question: if 12C
makes up 98.89% of C, and 13C is 1.11%,
calculate the average atomic mass of C:
Mass from 12C atoms
12 x 0.9889
11.8668
+ Mass from 13C atoms
+ 13 x 0.0111
+
0.1443
= 12.01
Mass from 35Cl + Mass from 37Cl
35 x 0.7553
+ 37 x 0.2447
26.4355
+
9.0539
= 35.49
Mass from 39K
39 x 0.9310
36.309
+ Mass from 41K
+ 41 x 0.0690
+
2.829
= 39.14
Mass from 40Ar + Mass from 36Ar + Mass from 38Ar
40 x 0.9960 + 36 x 0.0034 + 38 x 0.0006
+
0.0228
39.84
+
0.1224
= 39.99