Chemistry Revision

• What is the smallest part of an element that can exist?


  An atom
• What is the approximate radius of an atom?


  About 0.1 nm (1 x 10^-10 m)
• How does the radius of a nucleus compare to that of an atom?


  The radius of a nucleus is less than 1/10,000 of that of the atom
• How many different elements are there approximately?


  About 100
• What represents atoms of each element?


  A chemical symbol
• What is a compound and how can it be represented?


  • A compound contains two or more elements chemically combined in fixed proportions.
  • It can be represented by formulae.
  • Compounds can only be separated into elements by chemical reactions.
• What is a mixture and how can it be separated?


  • A mixture consists of two or more elements or compounds not chemically combined.
  • The chemical properties of each substance remain unchanged.
  • Mixtures can be separated by physical processes such as:
  • Filtration
  • Crystallisation
  • Simple distillation
  • Fractional distillation
  • Chromatography
• What are the relative charges and masses of protons, neutrons, and electrons?


  • Proton: Relative Charge +1, Relative Mass 1
  • Neutron: Relative Charge 0, Relative Mass 1
  • Electron: Relative Charge -1, Relative Mass Very small
• How does the number of electrons compare to the number of protons in an atom?


  The number of electrons is equal to the number of protons
• What is the atomic number of an element?


  The atomic number is the number of protons in an atom of an element
• What is the mass number of an atom?


  The mass number is the sum of the protons and neutrons in an atom
• What are isotopes?


  Isotopes are atoms of the same element that have different numbers of neutrons
• What does relative atomic mass represent?


  It is an average value that takes account of the abundance of the isotopes of the element
• How do electrons occupy energy levels in an atom?


  Electrons occupy the lowest available energy levels
• How can the electronic structure of an atom be represented?


  By numbers or by a diagram
• What is the electronic structure of sodium?


  2,8,1