1. 4/2003 Rev 2 I.2.1 – slide 1 of 29 Session I.2.1 Part I Review of Fundamentals Module 2Basic Physics and Mathematics Used in Radiation Protection Session 1Basic Atomic Structure IAEA Post Graduate Educational Course Radiation Protection and Safe Use of Radiation Sources

2. 4/2003 Rev 2 I.2.1 – slide 2 of 29 Overview  In this session we will discuss the building blocks of the atom including the Neutron, Proton and Electron  We will also discuss how the Atomic Number specifies the elements and how they are arranged in the Periodic Table  Finally, we will discuss how Isotopes of an element have different Atomic Mass

3. 4/2003 Rev 2 I.2.1 – slide 3 of 29 Atom  positively charged (+) protons,  uncharged neutrons and  negatively charged (-) electrons The atom is composed of:

4. 4/2003 Rev 2 I.2.1 – slide 4 of 29 Atom Thomson’s Model Rutherford’s Model

5. 4/2003 Rev 2 I.2.1 – slide 5 of 29 Atom Bohr’s Model

6. 4/2003 Rev 2 I.2.1 – slide 6 of 29 Nucleus Protons and neutrons together form the nucleus of the atom. The nucleus determines the identity of the element and its atomic mass. Proton and neutrons have essentially the same mass but only the proton is charged while the neutron has no charge.

7. 4/2003 Rev 2 I.2.1 – slide 7 of 29 Protons Protons are positively charged particles found inside the nucleus of an atom. Each element has a unique atomic number (a unique number of protons). Proton number never changes for any given element. For example, oxygen has an atomic number of 8 indicating that oxygen always has 8 protons.

8. 4/2003 Rev 2 I.2.1 – slide 8 of 29 Neutrons Neutrons are the other particle found in the nucleus of an atom. Unlike protons and electrons, however, neutrons carry no electrical charge and are thus "neutral." Atoms of a given element do not always contain the same number of neutrons.

9. 4/2003 Rev 2 I.2.1 – slide 9 of 29 Electrons Electrons are negatively charged particles that surround the nucleus in “orbits” similar to moons orbiting a planet. The sharing or exchange of electrons between atoms forms chemical bonds which is how new molecules and compounds are formed.

10. 4/2003 Rev 2 I.2.1 – slide 10 of 29 ELECTRON BINDING ENERGY  Electrons exist in discrete “shells” around the nucleus (similar to planets around the sun)  Each shell represents a unique binding energy holding the electron to the nucleus  The shells are designated by letters (K, L, M, N …) where K, the shell closest to the nucleus, has the largest binding energy, so the K electron is the most tightly bound  Maximum number of electrons in each shell: 2 in K shell, 8 in L shell …

11. 4/2003 Rev 2 I.2.1 – slide 11 of 29 ParticleSymbol Mass (kg) Energy (MeV) Charge Protonp1.672E-27938.2+1 Neutronn1.675E-27939.20 Electrone0.911E-300.511 Summary of the Atom

12. 4/2003 Rev 2 I.2.1 – slide 12 of 29 Atomic Mass Unit (amu) Where 1 amu is approximately equal to 1.6605 x 10 -24 grams

13. 4/2003 Rev 2 I.2.1 – slide 13 of 29 Atomic Mass Unit (amu) The atomic mass of the proton and the neutron is approximately: Proton = 1.6726 x 10 -24 grams = 1.0073 amu Neutron = 1.6749 x 10 -24 grams = 1.0087 amu Thus, the neutron is just a little heavier than the proton.

14. 4/2003 Rev 2 I.2.1 – slide 14 of 29 Atomic Mass Unit (amu) The difference in the mass of the neutron and the proton can be understood if we assume that the neutron is merely a proton combined with an electron forming a neutral particle slightly more massive than a proton alone.

15. 4/2003 Rev 2 I.2.1 – slide 15 of 29 Atomic Mass Unit (amu) The atomic mass of the electron is approximately: Electron= 9.1094 x 10 -28 grams = 0.00055 amu Thus, the electron has a much smaller mass than either the proton or the neutron, 1837 times smaller or about 2000 times smaller.

16. 4/2003 Rev 2 I.2.1 – slide 16 of 29 Elements The number of protons in an atom dictate the element. For an uncharged atom, the number of electrons equals the number of protons.

17. 4/2003 Rev 2 I.2.1 – slide 17 of 29 10 Most Abundant Elements ElementSymbolProtons Relative % of Earth’s Mass OxygenO846.6 SiliconSi1427.7 AluminumAl138.1 IronFe265.0 CalciumCa203.6 SodiumNa112.8 PotassiumK192.6 MagnesiumMg122.1 TitaniumTi220.4 HydrogenH10.1

18. 4/2003 Rev 2 I.2.1 – slide 18 of 29 In 1869, Russian chemist Dmitri Mendeleev first described an arrangement of the chemical elements now known as the periodic table. The periodic table displays all chemical elements systematically in order of increasing atomic number (the number of protons in the nucleus). Periodic Table of the Elements

19. 4/2003 Rev 2 I.2.1 – slide 19 of 29 Rare Earth Elements Actinide Series Lanthanide Series Periodic Table of the Elements

20. 4/2003 Rev 2 I.2.1 – slide 20 of 29

21. 4/2003 Rev 2 I.2.1 – slide 21 of 29 Sample Element - Zirconium 40 Zr Zirconium 91.2 Electron Shell Configuration: K1s-22 L2s-22p-68 M3s-23p-63d-1018 N4s-24p-64d- 210 O5s-22 10 + 18 + 12 = 40 K L M N O

22. 4/2003 Rev 2 I.2.1 – slide 22 of 29 Sample Element - Zirconium Name: Zirconium Symbol: Zr Atomic Number: 40 Atomic Mass: 91.224 amu Melting Point: 1852.0 °C Boiling Point: 4377.0 °C No. of Protons/Electrons:40 No. of Neutrons: 51 Classification: Transition Metal Phase at Room Temperature:Solid Density @ 293 K: 6.49 g/cm 3 Color: Grayish Date of Discovery: 1789 Discoverer: Martin Klaproth

23. 4/2003 Rev 2 I.2.1 – slide 23 of 29 Isotopes Atoms of an element that have a different number of neutrons in the nucleus are called isotopes of each other. Xy Z A Xy = element symbol A = atomic mass (neutron + protons) A = atomic mass (neutron + protons) Z = atomic number (protons) Z = atomic number (protons) isotope notation typically written as:

24. 4/2003 Rev 2 I.2.1 – slide 24 of 29 Isotopes The number of protons and electrons remain the same. But the number of neutrons varies.

25. 4/2003 Rev 2 I.2.1 – slide 25 of 29 Isotopes There are many isotopes. Most have more neutrons than protons. Some are stable but most are unstable (radioactive). equal number of protons and neutrons

26. 4/2003 Rev 2 I.2.1 – slide 26 of 29 Stable Nuclides long range electrostaticforces short range nuclear forces p p n Line of stability

27. 4/2003 Rev 2 I.2.1 – slide 27 of 29 Stable and Unstable Nuclides Too many neutrons for stability Too many protons for stability

28. 4/2003 Rev 2 I.2.1 – slide 28 of 29 Summary

29. 4/2003 Rev 2 I.2.1 – slide 29 of 29 Where to Get More Information  Cember, H., Introduction to Health Physics, 3 rd Edition, McGraw-Hill, New York (2000)  Firestone, R.B., Baglin, C.M., Frank-Chu, S.Y., Eds., Table of Isotopes (8 th Edition, 1999 update), Wiley, New York (1999)  International Atomic Energy Agency, The Safe Use of Radiation Sources, Training Course Series No. 6, IAEA, Vienna (1995)