ATOMS, IONS AND ISOTOPES

ATOMS, IONS AND ISOTOPES

1. ATOMIC NUMBER AND MASS NUMBER DESCRIBE THE ATOM

   • some periodic tables do the numbers the other way around, however all you need to remember is that the larger number is always the mass number
   • atoms of the same element all have the same number of protons - and so atoms of different elements will have different numbers of protons
   • on the periodic table the mass number is usually written as the relative atomic mass
   • neutral atoms have no charge (unlike ions ) this is because they have the same number of protons and electrons, the charge on the electrons is the same size as the charge as the charge on the protons - so the charges cancel out
     • so the number of electrons on a neutral atom is equal to the atomic number
       • SO BASICALLY EVERY NATURALLY OCCURRING ELEMENT ( EVERY ELEMENT ON THE PERIODIC TABLE) ARE NEUTRAL THEY CONTAIN THE SAME NUMBER OF PROTONS AND ELECTRONS

2. IONS HAVE DIFFERENT NUMBERS OF PROTONS AND ELECTRONS

   • ions form when atoms or groups of atoms GAIN or LOSE electrons
     • NEGATIVE ions form when atoms gain electrons - they have more electrons than protons
     • POSITIVE ions form when an electron is lost - there are more protons than electrons
     • f- = there is a single negative charge, so there must be one more electron than protons
       • F - has an atomic number of 9, so has 9 protons --- f- must have 9+1 =10 electrons
         • FE+2 ----- there is a 2+ charge so there must be two more protons than electrons (meaning that the atom has lost 2 electrons
           • FE has an atomic number of 26, so it has 26 protons --so FE2+ must have 26-2 = 24 electrons

3. ISOTOPES ARE THE SAME EXCEPT FOR THE NUMBER OF NEUTRONS

   • ISOTOPES ARE DIFFERENT FORMS OF THE SAME ELEMENT, WHICH HAVE THE SAME NUMBER OF NEUTRONS
     • for example carbon 12 has
       • an atomic number of 6 meaning there are 6 protons and 6 electrons
         • the atomic mass is 12 so there are 6 neutrons
     • and carbon 13 has
       • an atomic number of 6 (as if it didn't have an atomic number of 6 it wouldn't be carbon)
         • so it would have 6 protons and 6 electrons
           • and as the atomic mass is 13 the neutron number is 7
     • another example is carbon 14
       • this as all carbon atoms do has an atomic number of 6
         • which means there are 6 protons and electrons
           • the atomic mass however is 14 so there are 8 neutrons
   • ISOTOPES HAVE THE SAME ATOMIC NUMBER BUT DIFFERENT MASS NUMBERS
     • IF THEY HAD DIFFERENT ATOMIC NUMBERS THEN THEY WOULD BE DIFFERENT ELEMENTS ALTOGETHER
       • HERE IS AN EXAMPLE CARBON

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