Atomic Structure

Atomic Structure

1. The nucleus

   • Protons
     • Charge +1, mass 1
     • No of protons determines what element an atom is
       • No. of protons = no. of electrons = atomic no.
   • Neutrons
     • Charge 0, mass 1
     • Isotopes of an element have the SAME NO OF PROTONS BUT DIFFERENT NOS OF NEUTRONS

2. Electrons

   • Charge -1, mass 0
     • ATOMS of an element have equal numbers of protons and electrons
       • Atoms can gain or lose electrons to become IONS
         • Metal atoms lose electrons to become positive ions
           • The number of charges on an ion formed by a metal is equal to the group number of the metal
         • Non-metal atoms gain electrons to become negative ions
           • The number of charges formed by a non-metal is equal to the group number - 8
   • Orbit the nucleus in energy "levels" or "shells"
     • A full outer energy shell is stable
       • Noble gases have full outer shells and are unreactive or
     • Electrons fill the inner energy levels before filling the outer energy levels
       • Maximum no of electrons in each energy level = 2,8,8
     • Valency = number of electrons the atom gains or loses to become stable
       • Valency for groups 1-4 = the group number. e.g valency of group 2 is 2
       • Valency for groups 5-0 = 8- group number. e.g group no 6 valency is 8-6 = 2

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