Atomic structure and isotopes

• Proton


  Positively charged particle in atomic nucleus. Has a relative mass of 1 and a relative charge of +1. It's symbol is p+.
• Work out number of protons

  Number at the top (atomic number)
• Neutron


  Neutral particle in atomic nucleus. Can be though of as providing the glue that holds the nucleus together despite the electrostatic repulsion between it's positively charged protons. Has a relative mass of 1 and a relative charge of 0. It's symbol is n.
• Work out number of neutrons

  Top-bottom (Atomic mass-atomic number)
• Electron


  Negatively charged particle surrounding nucleus. It has a relative mass of 1/2000 and a relative charge of -1. It's symbol is e-.
• Work out number of electrons

  Number at the top (atomic number).
• Nucleus


  Central part of an atom containing protons and neutrons.
• Atomic Number (proton number) (Z)

  Number of protons in an atom's nucleus. Must be a whole number. The top number next to the symbol on the periodic table.
• Mass Number (A)


  Total number of particles (protons and neutrons) in nucleus. Greater than the atomic number. Must be a whole number. The bottom number next to the symbol on the periodic table.
• Nucleons


  Collective term for protons and neutrons.
• Isotope


  Atoms of same element with the same number of protons and electrons but different number of neutrons and different atomic masses.
• What do chemical reactions of isotopes involve?

  Electrons surrounding the nucleus.
• Do different isotopes of the same element have the same chemical properties?

  Yes, they have the same number of electrons and therefore react in the same way.
• What is the effect of the number of neutrons on chemical reactions?

  The number of neutrons has no effect on reactions because they have no charge.
• What differences may exist between isotopes of the same element?

  There may be some differences in physical properties.
• How does the mass of an isotope affect its boiling point, melting point, and density?

  A higher mass of an isotope means it has a higher boiling point, melting point, and density.
• Relative Atomic Mass (Ar)

  The weighted mean mass of an atom of an element compared with 1/12 of the mass of an atom of carbon-12. It's the value we see on the periodic table.
• Relative Isotopic Mass


  The mass of an atom of an isotope compared with 1/12 of the mass of an atom of carbon-12 (which is exactly 12 mol)
• Weighted Mean Mass


  An average of the relative masses of the isotopes that exist for an element. It takes into account the percentage abundance of each isotope and the relative isotopic mass of each isotope. Relative masses have no units as they are a ratio of two masses.
• Cation


  Positively charged ion formed by losing electrons. Number of electrons=Atomic number-charge
• Anion


  Negatively charged ion formed by gaining electrons. Number of electrons=Atomic number+charge
• What is a mass spectrometer?

  A device for measuring relative isotopic masses and abundances of isotopes of elements.
• What happens to a sample in a mass spectrometer?

  The sample is vaporised and ionised to become unipositive (1+ ion).
• How are ions separated in a mass spectrometer?

  Heavier ions move slower than lighter ions and are more difficult to deflect.
• What is detected in a mass spectrometer?

  Ions are detected according to their relative mass to charge ratio (M/Z).
• What does a mass spectrum record?

  It records the mass of the +1 ions as the mass to charge ratio (M/Z) on the x-axis and the abundance of each isotope on the y-axis.
• How is relative abundance represented in a mass spectrum?

  The greater the abundance of ions, the greater the signal.
• Mass to Charge Ratio (m/z)

  Ratio used in mass spectrometry for isotopes.
• Ionic Solid


  Solid composed of ions held by electrostatic forces.
• Ionic Solution


  Solution where ions are separated and free to move.
• Percentage Abundance


  Proportion of each isotope in a sample.
• Relative masses of compounds

  The sum of Ar of each atom in a compound to one decimal place. Compared with 1/12 of the mass of an atom of carbon-12.
• Relative molecular mass (RMM)

  The average (weighted mean) mass of a covalent molecule relative to 1/12 of the mass of an atom of carbon-12.
• Calculate relative molecular mass (Mr)

  Relative atomic mass x number of atoms
• Relative Formula Mass (RFM)

  The average (weighted mean) mass of ionic compounds of a formula unit relative to one-twelfth of the mass of an atom of carbon-12
• Calculate relative formula mass

  Relative atomic mass x number of atoms
• Calculating relative atomic mass for mass spectrometry data

  Sum of all (peak height x its mass)/sum of all peak heights
• Calculate relative isotopic mass

  (Isotopic mass x relative abundance) + (Isotopic mass x relative abundance)/ 100
• Ion


  Charged particles formed when atoms lose or gain electrons. They have completely different chemical properties from their atoms. They are bonded to ions of the opposite charge in ionic solids and are separate in ionic solutions.