2. Topic 3 – Atomic Theory B Gilday – St Thomas Aquinas Secondary The nucleus (centre of an atom) contains protons and neutrons Protons have a one positive charge Neutrons have no charge Electrons have a negative charge and orbit the nucleus

3. Topic 3 – Atomic Theory B Gilday – St Thomas Aquinas Secondary ProtonsElectrons The number of negative electrons in an atom is the same as the number of positive protons. So atoms are NEUTRAL They have no charge Neutral Atoms

4. Topic 3 – Atomic Theory B Gilday – St Thomas Aquinas Secondary Na Cl Electron arrangements for all elements are in the data book. 2)8)12)8)7 First electron shell Second electron shell Third electron shell

5. Topic 3 – Atomic Theory B Gilday – St Thomas Aquinas Secondary Na Atomic Number and Mass Number may be given in a question 23 11 Mass number Atomic number Atomic Number = number of protons = number of electrons Mass Number = number of protons + number of neutrons Number of neutrons = Mass Number – Atomic Number p = 11e = 11n = 23 –11 = 12

6. Topic 3 – Atomic Theory B Gilday – St Thomas Aquinas Secondary Ions are formed when atoms gain or lose electrons to achieve a full outer shell Metals form positive ions Non-metals form negative ions Na 2)8)1 Na + 2)8) Loses one electron

7. Topic 3 – Atomic Theory B Gilday – St Thomas Aquinas Secondary Ions are formed when atoms gain or lose electrons to achieve a full outer shell Metals form positive ions Non-metals form negative ions Cl 2)8)7 Cl - 2)8)8 Gains one electron

8. Topic 3 – Atomic Theory B Gilday – St Thomas Aquinas Secondary Ions are formed when atoms gain or lose electrons to achieve a full outer shell Metals form positive ions Non-metals form negative ions Mg 2)8)2 Mg 2+ 2)8) Loses two electrons

9. Topic 3 – Atomic Theory B Gilday – St Thomas Aquinas Secondary Ions are formed when atoms gain or lose electrons to achieve a full outer shell Metals form positive ions Non-metals form negative ions N 2)5 N 3- 2)8) Gains 3 electrons

10. Topic 3 – Atomic Theory B Gilday – St Thomas Aquinas Secondary Ions are formed when atoms gain or lose electrons to achieve a full outer shell Metals form positive ions Non-metals form negative ions Al 2)8)3 Al 3+ 2)8) Loses 3 electrons

11. Topic 3 – Atomic Theory B Gilday – St Thomas Aquinas Secondary Ions are formed when atoms gain or lose electrons to achieve a full outer shell Metals form positive ions Non-metals form negative ions S 2)8)6 S 2- 2)8)8 Gains two electrons

12. Topic 3 – Atomic Theory B Gilday – St Thomas Aquinas Secondary A Li + B K + C Mg 2+ D Cl - E F - F O 2- Which ions have the same electron arrangement as argon? Argon has electron arrangement 2)8)8 2)8)8)12)8)82)8)22)8 2)8)72)8)8 2)72)82)62)8 2)12)

13. Topic 3 – Atomic Theory B Gilday – St Thomas Aquinas Secondary Cl 35 17 Cl 37 17 Isotopes are different types of the same element Mass number is different Atomic number is the same p = 17 e = 17 n = 35-17 =18 p = 17 e = 17 n = 37-17 =20 They have different numbers of neutrons

14. Topic 3 – Atomic Theory B Gilday – St Thomas Aquinas Secondary Relative Atomic Mass The relative atomic mass of an atom is the average mass of the atom. It depends on the number of isotopes and how much of each isotope there is (percentage abundance). In chlorine 75% consists of the 35 isotope and 25% consists of the 37 isotope. Mass of 100 Cl atoms = Mass of 35 isotopes + mass of 37 isotopes = 75 x 35+ 25 x 37 = 2625+ 925 = 3550 atomic mass units Average mass of one Cl atom= 3550 / 100 = 35.5 amu