The Atom

The Atom

1. made up of protons, neutrons and electrons

   • electrons
     • -1 charge
     • extremely small relative mass
     • in shells around nucleus
   • nucleus
     • protons
       • +1 charge
       • 1 relative mass
     • neutrons
       • 0 charge
       • 1 relative mass

2. nuclear symbols

   • mass number
     • i.e. Na = 23
     • total number protons + neutrons
   • Atomic number
     • number of protons in nucleus
     • i.e. Na = 11

3. Ions= different numbers of protons & electrons

   • negative
     • more electrons than protons
     • i.e. Br-
   • positive
     • fewer electrons than protons
     • i.e. Mg2+

4. Isotopes

   • atoms with the same number of protons & different numbers of neutrons
   • i.e. Chlorine-35 and Chlorine-37
   • the same atomic number
   • different mass number
   • number and arrangement decides chemical properties
     • same configuration = same properties
   • slightly different physical properties
     • often depend on mass of atom

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