Atomic structure – cont
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Elements are defined by their number of protons. Isotopes of an element have the same number of protons but different numbers of neutrons, giving them different atomic masses but the same chemical properties. Chlorine, for example, has two common isotopes - chlorine-35 with 17 protons, 18 neutrons, and chlorine-37 with 17 protons and 20 neutrons. The relative atomic mass of an element is calculated based on the natural abundance of its isotopes and is measured in atomic mass units relative to carbon-12. Electrons in atoms are arranged in discrete energy levels and orbit the nucleus rather than having a defined location.
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Atomic structure – cont
- 2. Isotopes Elements are defined by the number of protons (atomic #, Z). Atoms of an element with the same # of protons and electrons, but different # of neutrons. ◦ Same atomic # (Z) but different mass # (A) ◦ Same chemical properties, however some are radioactive
- 4. Isotopes - chlorine Chlorine Protons Electrons Neutrons n
- 5. Isotopes - chlorine Chlorine Protons Electrons Neutrons n 17 17 17 17
- 6. Isotopes - chlorine Chlorine Protons Electrons Neutrons n 17 17 35-17=18 17 17 37-17 = 20
- 8. Relative Atomic Mass (Ar) oHow we compare the mass of atoms oBased on Carbon atom oAtomic mass units (amu) Element Ar H 1 C 12 O 16 Mg 24 Cl 35.5
- 9. Relative Atomic Mass (Ar) Calculate the relative atomic mass (Ar) or Chlorine. 25 % 75 % (75x35) + (25x37)= 35.5 amu 100
- 10. Arrangement of Electrons in Atoms Electrons move very fast around the nucleus It is impossible to pinpoint their location Electrons are arranged in energy levels and cannot be between them.
- 11. Arrangement of Electrons in Atoms 1st level – 2 2nd level – 8 3rd level – 18 (when 8 are present next two jump to level-4, then following return to level-3) 4th level - 2
- 12. Arrangement of Electrons in Atoms Bohr-Rutherford Diagrams