Atoms, ions, and compounds

• Proton


  Subatomic particle found in the nucleus of an atom
• The nuclear atom


  Model of the atom where the nucleus is made up of protons and neutrons, with electrons orbiting the nucleus
• Electron


  Subatomic particle that occupies a region outside the nucleus of an atom
• Protons, neutrons, and electrons are the three types of subatomic particles
• Protons, neutrons, and electrons

  • Protons and neutrons make up the nucleus, electrons orbit the nucleus
  • Protons have a positive charge, electrons have a negative charge, neutrons have no charge
• Atoms and their subatomic particles have tiny masses
• Relative mass


  Comparing the masses of subatomic particles, rather than using grams
• A proton has virtually the same mass as a neutron
• An electron has negligible mass, about 1/1836 the mass of a proton
• A neutron has a slightly greater mass than a proton, by a factor of 1.001375
• Charge


  Protons have a positive charge, electrons have a negative charge, neutrons have no charge
• The charge on a proton is +1.60217733 x 10-19 C, the charge on an electron is -1.60217733 x 10-19 C
• Atoms contain the same number of protons as electrons, making them neutral overall
• Neutrons provide the 'glue' that holds the nucleus together despite the electrostatic repulsion between protons
• Most atoms contain the same number of or slightly more neutrons than protons
• Atomic number


  The number of protons in an atom, which identifies the element
• As of 2014, the existence of 114 elements has been confirmed, and others have been tentatively reported
• Every atom of the same element contains the same number of protons
• Different elements contain atoms with different numbers of protons
• Isotopes


  Atoms of the same element with different numbers of neutrons and different masses
• Most elements are made up of a mixture of isotopes
• Representing isotopes


  Using the chemical notation: element symbol, mass number, atomic number
• The number of neutrons has no effect on the chemical reactions of an element
• Different isotopes of an element react in the same way chemically
• Higher-mass isotopes of an element have a higher melting point, boiling point, and density
• Heavy water


  Water containing the deuterium isotope of hydrogen instead of regular hydrogen
• Heavy water has slightly different physical properties compared to regular water
• Tritium is a third isotope of hydrogen, containing two neutrons
• Ions


  Charged atoms, with a different number of electrons than protons
• Cations


  Positive ions, with fewer electrons than protons
• Anions


  Negative ions, with more electrons than protons
• Ions are always shown with their overall relative charge
• Ions of the same element have the same number of protons but a different number of electrons
• Relative isotopic mass


  Has no units because it is a ratio of two masses
• Relative isotopic masses


  • Accurate
  • One decimal place
• Isotope


  Defined by its mass number (number of protons and neutrons)
• For A Level chemistry, you will be working with masses to one decimal place
• In most cases, you can assume that the relative isotopic mass is the same as the mass number A of the isotope
• Relative atomic mass


  The weighted mean mass of an atom of an element relative to 1/12 of the mass of an atom of carbon-12
• Determination of relative atomic mass

  1. The percentage abundances of the isotopes in a sample of an element are found experimentally using a mass spectrometer

  2. A sample is placed in the mass spectrometer

  3. The sample is vaporised and then ionised to form positive ions

  4. The ions are accelerated, heavier ions move more slowly and are more difficult to deflect than lighter ions, so the ions of each isotope are separated

  5. The ions are detected on a mass spectrum as a mass-to-charge ratio