1. How Many Neutrons? It is not strictly true to say that elements consist of one type of atom. Which sub-atomic particle must always be of the same number in atoms of an element? Remember: The number of protons defines the element

2. Atoms of the same element always have the same number of protons, but they may have different numbers of neutrons. isotopes.Atoms that differ in this way are called isotopes.

3. Write this down! Isotopes are atomic forms of the same element, with the same number of protons but differing numbers of neutrons.

4. Isotopes are virtually identical in their chemical reactions. WHY? The uncharged neutrons make no difference to chemical properties but do affect physical properties such as melting point and density.

5. Isotopes: Carbon Natural samples of elements are often a mixture of isotopes. About 1% of natural carbon is carbon-13. Protons Electrons Neutrons C 12 6 99% C 13 6 1% 666666 667667

6. Isotopes: Hydrogen Hydrogen exists as 3 isotopes although Hydrogen-1 makes up the vast majority of the naturally occurring element. H 1 1 H 2 1 H 3 1 Protons Electrons Neutrons Hydrogen Protons Electrons Neutrons (Deuterium) Protons Electrons Neutrons (Tritium)

7. Isotopes: Chlorine About 75% of natural chlorine is 35 Cl the rest is 37 Cl. Cl 35 17 75% 17 Protons Electrons Neutrons 17 18 Protons Electrons Neutrons 17 20 Cl 37 17 25%

8. Isotopes of Oxygen Almost all of natural oxygen is 16 O but about 0.2% is 18 O. Produce a Table showing the particles in each isotope. Protons Electrons Neutrons 16 O 8 Oxygen-18Oxygen-16 8 8 8 Protons Electrons Neutrons 8 8 10 Activity

9. Isotopes and Relative Atomic Mass Many natural elements are a mixture of isotopes, so when we react them we are using a mixture of atoms with different mass numbers. The relative atomic mass given in the periodic table takes account of this. E.g.. For 100 atoms of chlorine: Mass of 75 atoms of Chlorine 35: 75 x 35 =2625 Mass of 25 atoms of Chlorine 37: 25 x 37 =925 Total = 3550 35.5 Average(divide by 100)= 35.5

10. Relative Atomic Mass Bromine contains 50.5% bromine-79 and 49.5% bromine-81. Calculate the relative atomic mass of natural bromine showing your working. Egg. For 100 atoms of bromine: Mass of 50.5 atoms of bromine 79: 50.5 x 79 =3989.5 Mass of 49.5 atoms of bromine 81: 49.5 x 81 =4009.5 Total = 7999 Average(divide by 100)= 80 Activity

11. 1.Which of the following is not a sub- atomic particle? A.Proton. B.Isotope. C.Neutron. D.Electron.

12. 2.The element Cobalt has a relative atomic mass of 59 and an atomic number of 27. Which of these is a true statement about each neutral cobalt atom? A.It contains 59 neutrons. B.It contains 27 electrons. C.It contains 32 protons. D.It contains equal numbers of neutrons and electrons.

13. 3.The Periodic Table displays iron as shown below. This indicates that Fe atoms: A.contain 56 neutrons. B.contain 30 electrons. C.contain 26 protons. D.contains more protons than neutrons. 56 Fe 26

14. 4.Bromine consists of a mixture of two isotopes: Bromine-79 and Bromine-81 Which of the following is true: A.Both isotopes contain 35 protons. B.Bromine 79 contains 46 neutrons. C.Bromine 81 contains 44 neutrons. D.Bromine-81 is more reactive than bromine- 79. 80 Br 35

15. 5.Natural boron consists of approx. 20% boron-10 and 80% boron-11. What will the relative atomic mass of natural boron will be? A.10.0 B.11.0 C.10.5 D.10.8 ?B5?B5