1. Electron cloud Nucleus consisting of protons and neutrons

2. Electron: It carries a negative charge. It has a mass only about 1/1850 of the proton. Nucleus consisting of protons and neutrons Electron cloud It is orbiting the nucleus at high speeds. Proton: It is found in the nucleus. It carries a positive charge.

3. Neutron: It does not carry any charge. It has about the same mass as a proton. Nucleus consisting of protons and neutrons Electron cloud

4. Atoms of different elements have different number of protons, electrons and neutrons. Example:

5. The atomic number is the number of protons in an atom.

6. Mass number: It is the total number of protons and neutrons in the nucleus of an atom.

7. For any neutral atom, the number of electrons is equal to the number of protons.

8. Data for atoms of the first 20 elements

9. Draw a labelled diagram to show the structure of an atom. Nucleus consisting of protons and neutrons Electron cloud

10. What is the charge of electron? What is the charge of proton? Compare the mass of electron and that of proton. Describe the movement of electron in an atom. Electron: It carries a negative charge. It carries a positive charge. It is orbiting the nucleus at high speeds. Electron has a mass only about 1/1850 of the proton.

11. What is the charge of a neutron? Compare the mass of neutron and that of proton. Neutron: It does not carry any charge. They have about the same mass. The atomic number is the number of protons in an atom. How do you know atomic number of an atom from the number of protons?

12. 1. Complete the following table.

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14. 2. Complete the following table for three element A, B and C

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16. 3. Complete the following table.

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18. It is the distribution of electrons in the various shells of an atom. 1st shell (energy level) 4th shell (energy level) 3rd shell 2nd shell nucleus

19. Energy of the electron in the first shell is lower

20. nucleus Energy of the electron in the third shell is higher

21. The first shell can hold a maximum of 2 electrons

22. The second shell can hold a maximum of 8 electrons

23. The third shell can hold a maximum of 18 electrons

24. The following rules can be applied to find out the electronic configuration of an atom. The first 2 electrons go into the first shell and complete it. The next 8 electrons go into the second shell and complete it. The next 8 electrons go into the third shell. The next 2 electrons go into the fourth shell. The next 10 electrons go into the third shell and complete it.

27. Electron diagrams also show the distribution of electrons in atoms. E.C.: 1 For example, hydrogen atom

28. E.C. : 2, 1 Lithium atom, atomic no. = 3

29. Sodium atom, atomic no. = 11 E.C. : 2, 8, 1

30. E.C. : 2, 8, 8, 2 Calcium atom, atomic no. = 20

31. Beryllium atom E.C. : 2, 2 Work out electronic configuration and electron diagram for beryllium, atomic no.=4

32. E.C. : 2, 7 Work out electronic configuration and electron diagram for fluorine atom, atomic no.=9

33. Work out electronic configuration and electron diagram for aluminium, atomic no.=13 E.C.: 2, 8, 3

34. Potassium atom, atomic no. = 19 E.C.: 2, 8, 8, 1

35. atomic number mass number

36. atomic number mass number

37. atomic number mass number

39. 3.5Isotopes Isotopes are atoms of a particular element with the same number of protons and electrons but a different number of neutrons. Three isotopes of hydrogen. 1 1 H 2 1 H 3 1 H

40. 3.5Isotopes Isotopes of an elements have the same number of electrons, therefore the same electronic configuration. Two isotopes of chlorine 35 17 Cl 37 17 Cl They have different mass numbers.

41. Which of the following are isotopes of the same element? Explain. A, C are isotopes of an element. B, D are isotopes of another element. Atoms A and atom C have the same number of protons but of different number of neutrons.