Atomic Structure

Atomic Structure

1. Atom

   • X, A (top)and Z(bottom)
     • A is the mass number
     • X is the symbol of element
     • Atomic Number
     • Number of protons= Number of electrons = Z
     • Number of neutrons= A- Z
   • Ions
     • When an atom loses electrons it forms a positive ion or cation
     • Negative ions or anions are formed when atom gain electrons
   • Radio Isotopes
     • Carbon 14 dating
       • it has eight neutrons. It can reduce the neutrons to proton ratio when a neutron changes to a proton and an electron
         • The rate of decay is measure by its half life
       • The amount of carbon 14 left when after an organisms die help the archaeologists to determine the age of ancient objects.
     • Cobalt 60
       • Commonly used for as it emits very penetrating gamma radiation, when its protons and neutrons change their relative positions in the nucleus.
         • Can treat localized tumours such as cancers and Leukaemia.
     • Iodine 131
       • emmits beta and gama rays, can be in the form of compound sodium iodide to investigate activity of the thyroid glands and diagnose and treat thyroid cancer.
       • has a short half life of eight days

2. Mass Spectometer

   • Ionization: the atoms hit with high energy electrons which knock out electrons producing positively charged ions
   • Vaporization: A vaporized sample is injected into the instruments. This allows the individual atatoms of the element to be analyzed
   • Acceleration: the positive ions are attracted to negatively charged plates. They are accelerated by an electric field and pass through a hole in the plate
   • Deflection: The accelerated positive ions are deflected using magnetic field place at the right angles to their path. The amount of deflection is proportional to the charge/mass ratio. Ions with smaller mass deflected more than heavier ions. Higher charges are deflected more
   • Detection: Positive ions of a particular mass/charge ratio are detected and a signal sent to a recorder. The strength of the signal is a measure of the number of ions with that charge/mass ratio that are detected.
   • Relative atomic mass= average mass of atom = total mass/number of atoms
     • Example: Boron 10 and Boron 11. Find the abundances of the two isotopes
       • Solution
         • Boron 10 = 19% and Boron 11= 81%

3. Electron arrangement

   • Continuous spectrum
     • shows different wavelength or colors
   • Line spectrum
     • Shows some colors of the continuous spectrum
   • Hydrogen spectrum
   • Electron arrangement of the first 10 elements
     • Represents the outer electrons called valence electrons on each energy level

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