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# Atomic structure

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• The relative mass of an electron is negligible.
• Emphasis should be on the proton number being unique for each element, like that of an identification (ID) number.
• Help students locate proton number from Periodic Table – bottom left corner.
• 1. (a) Nitrogen – 7; (b) Helium – 2; (c) Sulfur – 16.
2. ( a) 17 – Chlorine; (b) 3 – Lithium; (c) 20 – Calcium.
• They each have one proton.
They have different numbers of neutrons.
• Although the mass of an atom is determined by the sum of protons and neutrons, the mass of an atom of an element is not always a whole number (eg. Cl – 35.5). The mass of an atom of an element is an average mass of the isotopes that make up the element. The percentage abundance is used to calculate the average mass.
• Clicking on the URL button will link you to &lt;http://www.youtube.com/watch?y=zEX2aGpIDBY&gt;, a website with a video on protons, neutrons, electrons and isotopes. It reviews the chemical makeup of elements. (The video is approximately 4.5 minutes long.)
Clicking on the URL button will link you to &lt;http://www.youtube.com/watch?v=K5Ks2X5TphI&gt;, a website with a video on the uses of radioactive isotopes. It outlines the uses of common radioactive isotopes. (The video is approximately 3.4 minutes long.)
• To show the electronic structure of an atom:
Indicate the number of protons and neutrons.
Infer the number of electrons.
Fill electrons starting from the 1st shell.
• ### Atomic structure

1. 1. CHAPTER 5 Atomic Structure © 2013 Marshall Cavendish International (Singapore) Private Limited
2. 2. Chapter 5 Atomic Structure 5.1 Inside Atoms 5.2 The Proton Number and Nucleon Number 5.3 Isotopes 5.4 Arrangement of Electrons in Atoms 2
3. 3. 5.1 Inside Atoms Learning Outcomes At the end of this section, you should be able to: • state the relative charges and masses of a proton, a neutron and an electron; • describe the structure of an atom. 3
4. 4. 5.1 Inside Atoms What are Atoms Made up of? Atoms are made up of 3 sub-atomic particles: • protons; • neutrons; • electrons. 4
5. 5. 5.1 Inside Atoms Where are these Sub-Atomic Particles Found? Nucleus • protons (+ve) • neutrons (neutral) Shells around the nucleus • electrons (–ve) 5
6. 6. 5.1 Inside Atoms Proton • Represented by the letter, p • Found in the nucleus • Relative mass = 1 • Relative charge = +1 p 6
7. 7. 5.1 Inside Atoms Neutron • Represented by the letter, n • Found in the nucleus • Relative mass = 1 • Relative charge = 0 n 7
8. 8. 5.1 Inside Atoms Electro n • Represented by the letter, e e • Found in shells surrounding nucleus 1 • Relative mass = 1840 • Relative charge = –1 8
9. 9. 5.1 Inside Atoms Summary of Sub-Atomic Particles Particle Symbol proton p 1 +1 neutron n 1 0 e 1 1840 –1 electron Relative mass Relative charge 9
10. 10. Chapter 5 Atomic Structure 5.1 Inside Atoms 5.2 The Proton Number and Nucleon Number 5.3 Isotopes 5.4 Arrangement of Electrons in Atoms 10
11. 11. 5.2 The Proton Number and Nucleon Number Learning Outcomes At the end of this section, you should be able to: • define proton (atomic) number and nucleon (mass) number; • deduce the number of protons, neutrons and electrons in an atom; • interpret and use symbols that represent an A element’s nucleon and proton numbers (Z X ). 11
12. 12. 5.2 The Proton Number and Nucleon Number Proton Number (Z) The number of protons in an atom is called its proton number. It is also known as the atomic number. Since an atom is electrically neutral (i.e. has no overall charge), Proton number = number of electrons 12
13. 13. 5.2 The Proton Number and Nucleon Number Proton Numbers Each element has a unique proton number. Atoms of different elements have different proton numbers. Example Proton number of carbon = 6 Any atom with 6 protons must be a carbon atom. nucleus of a carbon atom 13
14. 14. 5.2 The Proton Number and Nucleon Number Where is the proton number of an element found in the Periodic Table? 23 Na Sodium 11 Proton number 14
15. 15. 5.2 The Proton Number and Nucleon Number Exercise 1. Find the proton number of the atoms of the following elements: (a) Nitrogen 7 (b) Helium 2 (c) Sulfur 16 2. Which element has a proton number of (a) 17? Chlorine (b) 3? Lithium (c) 20? Calcium 15
16. 16. 5.2 The Proton Number and Nucleon Number Nucleon Number (A) The total number of protons and number of neutrons in an atom is called the nucleon number. Nucleon number is also known as mass number. The mass of an atom depends on the number of protons and neutrons. Nucleon number (A) = number of protons + number of neutrons 16
17. 17. Chapter 5 Atomic Structure 5.1 Inside Atoms 5.2 The Proton Number and Nucleon Number 5.3 Isotopes 5.4 Arrangement of Electrons in Atoms 17
18. 18. 5.3 Isotopes Learning Outcome At the end of this section, you should be able to: • define isotopes. 18
19. 19. 5.3 Isotopes Isotopes of Hydrogen These are 3 atoms of hydrogen. Hydrogen-1 Hydrogen-2 Hydrogen-3 What are the similarities and differences of these 3 atoms? 19
20. 20. 5.3 Isotopes What are Isotopes? Isotopes are atoms of the same element with the same number of protons but different numbers of neutrons. Example 1 Chlorine gas consists of 75% chlorine-35, 25% chlorine-37. 20
21. 21. 5.3 Isotopes What are Isotopes? Example 2 14 6 C 13 6 C 12 6 C Carbon consists of 98.93% carbon-12, 1.07% carbon-13, and trace amounts of carbon14. 21
22. 22. 5.3 Isotopes Properties of Isotopes Isotopes have the same chemical properties but slightly different physical properties. Same chemical properties are due to • the same number of electrons; • only electrons involved in chemical reactions. 22
23. 23. 5.3 Isotopes Properties of Isotopes Different physical properties are due to • different relative atomic masses; • result in different densities, melting and boiling points. 23
24. 24. 5.3 Isotopes Uses of Isotopes Isotopes that emit high-energy radiation are called radioisotopes. They are radioactive substances. The radiation emitted is dangerous because it can damage living cells and cause cancer. 24
25. 25. 5.3 Isotopes Uses of Isotopes However, radioisotopes can have important applications and can be safely used if they are handled properly. For example, smoke detectors use a radioisotope. Smoke entering the smoke detector absorbs the radiation. This sets off an alarm in the smoke detector. 25
26. 26. 5.3 Isotopes Protons, Neutrons, Electrons and Isotopes Review Uses of Isotopes 26
27. 27. Chapter 5 Atomic Structure 5.1 Inside Atoms 5.2 The Proton Number and Nucleon Number 5.3 Isotopes 5.4 Arrangement of Electrons in Atoms 27
28. 28. 5.4 Arrangement of Electrons in Atoms Learning Outcome At the end of this section, you should be able to: • use diagrams to describe atoms as containing: – protons and neutrons in nucleus; – electrons arranged in the electron shells (energy levels). 28
29. 29. 5.4 Arrangement of Electrons in Atoms Electronic Structure Electrons move around the nucleus in regions known as electron shells. The 1st shell • is closest to the nucleus; • holds a maximum of 2 electrons; • is always filled first; • has the lowest energy level. 29
30. 30. 5.4 Arrangement of Electrons in Atoms Electronic Structure The 2nd shell • can hold up to 8 electrons; • has higher energy than 1st shell. The 3rd shell • can usually hold up to 8 electrons; • is filled up after the 2nd shell. 30
31. 31. 5.4 Arrangement of Electrons in Atoms Electronic Configuration/ Electronic Structure Electronic configuration/structure is the arrangement of electrons in an atom. Magnesium atom (Z = 12) 1st shell: 2 electrons 2nd shell: 8 electrons Nucleus 12p, 12n 3rd shell: 2 electrons Magnesium atom Electronic configuration = 2, 8, 2 31
32. 32. 5.4 Arrangement of Electrons in Atoms Valence Shell and Valence Electrons The valence shell or outer shell of an atom refers to the shell that is furthest away from the nucleus of the atom. Valence electrons are the electrons found in the valence shell. Valence shell/ outer shell Magnesium has 2 valence electrons Magnesium atom 32
33. 33. 5.4 Arrangement of Electrons in Atoms Valence Electrons The chemical properties of an element depend on the number of valence electrons. Example 1 Sodium (2, 8, 1) and Potassium (2, 8, 8, 1) • have similar chemical properties; • each has 1 valence electron. Example 2 Fluorine (2, 7) and Chlorine (2, 8, 7) • have similar chemical properties; • each has 7 valence electrons. 33
34. 34. 5.4 Arrangement of Electrons in Atoms The Periodic Table Elements are arranged in order of increasing proton number. 34
35. 35. 5.4 Arrangement of Electrons in Atoms The Periodic Table Horizontal rows of elements are called periods. Vertical columns of elements are called groups. 35
36. 36. 5.4 Arrangement of Electrons in Atoms Valence Electrons and the Periodic Table Elements with the same number of valence electrons belong to the same group in the Periodic Table. Sodium (2, 8, 1) and potassium (2, 8, 8, 1) belong to Group I. Fluorine (2, 7) and chlorine (2, 8, 7) belong to Group VII. Hence, elements in the same group of the Periodic Table have similar chemical properties. 36
37. 37. Chapter 5 Atomic Structure Concept Map 37
38. 38. Chapter 5 Atomic Structure The URLs are valid as at 15 October 2012. Acknowledgements (slide 1) © New Numerals CD (slide 25) heimrauchmelder © TDLacoste | Wikimedia Commons | CC BY-SA 3.0 (http://creativecommons.org/licenses/by-sa/3.0/deed.en) 38