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Atoms

Atoms. -Basics on atomic structure -Isotopes -Isotopic Mass & Relative Atomic Mass. Revision from Year 11. The Bohr model of the atom. It’s not perfect, but it is a simple model. Mass and charge.

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Atoms

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  1. Atoms -Basics on atomic structure -Isotopes -Isotopic Mass & Relative Atomic Mass

  2. Revision from Year 11 • The Bohr model of the atom. • It’s not perfect, but it is a simple model.

  3. Mass and charge • With your partner, try to describe the distribution of mass in an atom (i.e where is it and why?) • Do the same for charge, where is the charge distributed within an atom? • A diagram may help.

  4. The Atomic number. • Each element has a unique atomic number. This number tells us two things: • How many protons the atom has • How many electrons the atom has. Why are these numbers the same?

  5. Atomic Mass. • Try not to confuse the atomic MASS and the atomic NUMBER. • The Atomic Mass tells us how much stuff is in the atom. How many PROTONS and NEUTRONS it has. • Why might we ignore electrons when we talk about atomic mass?

  6. Atomic number & atomic mass • Atomic Mass • Found in the periodic table • Tells us the of protons AND neutrons in the nucleus • A larger number than the atomic number. • Atomic number • Found in the periodic table • Table arranged by increasing atomic number • Tells us the number of protons in the nucleus.

  7. We’re pretty lazy • We have a short way of writing the atomic number and the mass number for an element: • Which number is atomic number, which is the mass number?

  8. Isotopes. • Isotopes are elements of the same type but with different mass.

  9. Chlorine has two stable isotopes. • How many protons and neutrons does each have? Try the others. 35Cl 131I12C 37Cl 127I13C

  10. Carbon 12. It’s important. • 12C is used as a standard for the measurement of relative mass. • Atomic masses are measured using a unit called unified atomic mass unit. • This is a tiny number- 1 u is 1.66 x 10-27 • Mass of carbon atom- 12 u • So one twelfth of an atom of carbon is 1 u

  11. Relative isotopic mass • The Relative Isotopic Mass is the mass of an atom of an isotope compared to one twelfth of the mass of an atom of Carbon-12.

  12. Relative isotopic mass • The Relative Isotopic Mass is the mass of an atom of an isotope compared to one twelfth of the mass of an atom of Carbon-12. • The Relative Isotopic Mass is the mass of an atom of an isotope compared to one twelfth of the mass of an atom of Carbon-12.

  13. Relative atomic mass. Ar • In a lump of carbon we have 12C and 13C. • These weigh a different amount. • We use a ‘weighted mean mass’ to account for this. • This depends on: • The percentage abundance of the isotope • The relative mass of the isotope.

  14. Ar Definition • The relative atomic mass is the weighted mean mass of an atom of an element compared to one-twelfth of the mass of an atom of carbon-12

  15. Ar Definition • The relative atomic mass is the weighted mean mass of an atom of an element compared to one-twelfth of the mass of an atom of carbon-12 • The relative atomic mass is the weighted mean mass of an atom of an element compared to one-twelfth of the mass of an atom of carbon-12

  16. Ar • For example: • Boron contains 19.77% 10B and 80.23% 11B • Ar(B)= (19.77/100 x 10) + (80.23/100 x 11) = 1.977 + 8.8253 = 10.8023 u

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