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The nucleus (centre of an atom) contains protons and neutrons

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. The number of negative electrons in an atom is the same as the number of positive protons.

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The nucleus (centre of an atom) contains protons and neutrons

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  1. 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

  2. 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 Protons Electrons Neutral Atoms

  3. Na Cl 2)8)1 2)8)7 First electron shell Second electron shell Third electron shell Electron arrangements for all elements are in the data book.

  4. Atomic Number and Mass Number may be given in a question Mass number 23 Na 11 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 = 11 e = 11 n = 23 –11 = 12

  5. 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 Na+ Loses one electron 2)8)1 2)8)

  6. 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 Cl- Gains one electron 2)8)7 2)8)8

  7. 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 Mg2+ Loses two electrons 2)8)2 2)8)

  8. 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 N3- Gains 3 electrons 2)5 2)8)

  9. 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 Al3+ Loses 3 electrons 2)8)3 2)8)

  10. 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 S2- Gains two electrons 2)8)6 2)8)8

  11. Which ions have the same electron arrangement as argon? 2)1 2) 2)8)8 2)8)8)1 2)8 2)8)2 2)7 2)8 2)6 2)8 2)8)7 2)8)8 Argon has electron arrangement 2)8)8

  12. Isotopes are different types of the same element 35 Cl 37 Cl 17 17 Mass number is different Atomic number is the same p = 17 p = 17 e = 17 e = 17 n = 35-17 =18 n = 37-17 =20 They have different numbers of neutrons

  13. 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

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