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Presentation On Isotopes

Home > PowerPoint Slides > Presentation On Isotopes
Published in: Chemistry
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This PPT is suitable for the IGCSE and O Level Chemistry students. It only provides theoretical background of the topic. The practice questions, worksheets and topical questions will be discussed during the tutoring sessions

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  1. Isotopes Chemistry (IGCSE / O-Level)
  2. What will you learn in this lesson? • Isotopes • Characteristics of Isotopes • Calculating Relative Atomic Mass
  3. Isotopes • Atoms of the same element that have the same proton number but a different nucleon number because they have different numbers of neutrons in their nuclei. • Some isotopes are radioactive because their nuclei are unstable. They are called radioisotopes IIH Protium T r iti•rn
  4. Characteristics of Isotopes Isotopes are referred to using their mass numbers such as carbon-12, carbon-13 and carbon-14 @ electron @ proton neutron — nucleus isotopes Of hydrogen: hydrogen (1M), deuterium du) and tritium (311). Naturally Occurring Can be made artificially
  5. Characteristics of Isotopes (contd.) (99.99 + ) r.ëT-20 X'Ne 10 p 10 18 n cf , 1 n—n-21 C .2+) 17 20 17 12 IO
  6. Characteristics of Isotopes (contd.) • Isotopes of an element have the same chemical properties because they all have equal number of electrons • Some physical properties of isotopes are different, because of the different masses, such as density and rate of diffusion, : A (frozen Dao) Sinks in water (left). An ordinary ice cube floats (right).
  7. Characteristics of Isotopes (contd.) • Tritium and carbon-14 are radioactive. The imbalance of neutrons and protons in their nuclei causes them to be unstable so the nuclei break down (without applying any external energy), emitting certain types of radiations. They are known as radioisotopes
  8. Calculating Relative Atomic Mass It takes into account the proportions (abundances) of all the naturally occurring isotopes. Higher proportions of any isotope will largely contribute to the average mass. The average value of the mass of an atom of element is called relative atomic mass (Ar) Chlorine has two isotopes chlorine-35 and chlorine-37. They exist in the ratio of 3:1 i.e. chlorine-35 exists 75% and chlorine-37 exists 25%. The relative atomic mass of chlorine can be calculated by finding the total mass of 100 atoms Mass of 100 atoms of chlorine = (35 x 75) + (37 x 25) = 3550 Then the average mass of one atom = 3550/100 = 35.5 Thus, for chlorine relative atomic mass (Ar) = 35.5
  9. Calculating Relative Atomic Mass (contd.) uthWm has two 311. The relatrve abundance of these two Isotopes Is shown tn Floure 2A 10 Aiomicmass Figure 2-9: tsaopes of lithium.
  10. Calculating Relative Atomic Mass (contd.) 1. Look figure 2.9. The graph shows you that the lithium sample consists of 7.5% lithium-6 and 92S% lithium- 7. Step 2. Calculate the mass of 100 atoms by multiplying the mass of each isotope by its abundance. Total mass of 100 atoms of lithium (6 * 7.5) + (7 * 92.5) 692.5 Step 3. Calculate the average mass M one lithium atom by dividhg the total mass by 100. Average ma— of one lithilm atom 692.5 100 — 6.925 Step 4. Round yow answer to required level of accuracy. Relative atomic mass of [Mum = 6.9 (to significant figures) The isotopes of magnesium and their abundances are given in Table 2.5. magnesium-24 magnesium-25 magnesium-26 Table 2.5: Isotopes of magnesium. Symbol 24/ 12 Mg 25 / 12 Mg 26 / 12 Mg 78.6 10.1 11.3 Calculate the relative atomic mass of magnesium.
  11. Practice Questions 1 2 Iridium has two isotopes. These isotopes are iridium-191 and iridium-193. A natural sample of iridium consists of 37.3% Mum-191. Calculate the relative atomic mass of iridium from the data. Bromine Is an eternent with two isotopes: bromine-79 and bromine-81. usually, the relative atomic mass of bromtne is given as 80, What does this salue for the Ar of bromine tell you about the approximate proportions ofthe two isotopes in a natural sample?

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