Atomic theory

  • Atoms are composed of protons, electrons and neutrons.
    • Protons have a charge of +1
    • Electrons has -1
    • Neutrons are neutral
  • In a neutral atom, the number of electrons is equal to the number of protons
  • The atomic number (Z) is the number of protons in its nucleus.
  • The mass number (A) is the sum of the numbers of protons and neutrons in its nucleus
  • The structure of an atom can be represented as AZX
  • Isotopes are atoms with the same atomic number but different mass numbers
  • Ions are charged atoms.
    • Positive ions have more protons than electrons
    • Negative ions have more electrons than proton
  • The electrons of an atom can exist only in allowed energy levels, or shells
    • Each shell can accommodate a set amount of electrons, formula 2n2
    • The electron configuration can be represented in terms of the number of electrons in each shell e.g. potassium 2,8,8,1
    • Valence electrons¬†are those in the outermost shell
  • Matter can be classified into the following categories:
    • Elements – substances made up of only one type of atom
    • Compounds – substances composed of two or more elements chemically combined in fixed proportions
    • Mixtures – two or more substances mixed together in any proportion

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