Atomic Structure

Atomic Structure

1. Atoms

   • protons
     • relative charge: +1
     • relative mass: 1
   • neutrons
     • relative charge:0
     • relative mass:1
   • electrons
     • relative charge: -1
     • relative mas: 5.45*10^-3
   • atomic number: the number of protons in the nucleus of one atom
   • mass number: the total number of protons and neutrons in the nucleus of one atom

2. MASS SPECTROMETER

   • purpose
     • separate and identify isotopes
     • identify unknown compounds
   • 4 main steps
     • Ionization
       • an "electric gun" fires a beam of "high energy electrons" at the sample, knocking out electrons.POSITIVE IONS ARE FORMED.
       • X(g) + e- ------ X+ + 2e-
     • Acceleration
       • an "electric field" is used to speed up the positively charged ions.. the ions are focused into a beam by passing them through slits
     • Deflection
       • a "magnetic field" is used to deflect the ions, the smaller the mass of the ions the more they are reflected and vice versa
     • Detection
       • the ions collide with the detector, creating an electric current that is proportional to the abundance of each ion

3. Isotopes: atoms with the same number of protons but different number of neutrons

4. IONIZATION ENERGY: The enthalpy change when an electron is removed from the outer shell of a gaseous atom

   • TREND
     • increases across a period
       • Explanation: the nuclear charge increases.. the attraction between the nucleus and the outer electrons increases..the electrons experience similar shielding ( since they are in the same energy shell)
         • EXAMPLES
           • Mg --- Al ( downfall)..... the outer electrons of Al are in a 3p-orbital that is of higher energy than 3s-orbital, so less energy is required to remove the electrons
           • P---- S (downfall)..... the paired electrons in a p-orbital of S are paired so they repel each other and so are easily removed..that is why S has a lower ionization energy
     • decreases down a group
       • the distance between the nucleus and the outer electrons increases, therefore the force of attraction between the nucleus and the outer electrons is reduced, so less amount of energy is required to remove the outer electrons

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