Atoms, Ions and Compounds

• every atom of the same element have the same number of protons
• different elements have different atoms that contain different amount of protons
• isotopes


  atoms of the same element with different numbers of neutrons and different masses
• different isotopes react in the same way because different numbers of neutrons doesn't affect chemical reactions
• positive ions, cations, are atoms with fewer electrons than protons, and are attracted to the cathode. they have an overall positive charge
• negative ions, anions, are atoms with more electrons than protons, and are attracted to the anode. they have an overall negative charge.
• the standard mass for an atomic mass is 1u, the mass of 1/12th the mass of a carbon-12 atom
• 1u is approximately the mass of a proton or neutron
• relative isotopic mass is the mass of an isotope relative to 1/12th the mass of a carbon-12 atom
• ions and atoms of an element have the same number of protons but different numbers of electrons
• mass number (big)


  protons + neutrons
• atomic number (small)


  protons
• mass to charge ratio 


  relative mass of ion / relative charge of ion
• mass spectrometer - determining relative atomic mass


  sample placed in mass spectrometer

  sample vapourised then ionised to form positive ions

  ions accelerated; heavier ions move slowly and are more difficult to deflect, so ions of each isotope are seperated

  ions are detected on a mass spectrum as a mass to charge ratio. each ion reaching the detector adds to the signal. greater abundance = larger signal