1. Prepared by, THIRU KUMARI

2. Elements in Period 3 Electron arrangement Activity: Uses of semi-metals Trends of changes across the period 3 We will discuss about: Exercises 1Exercises 2

4. Elements in period 3 Chemical elements in the third period Group123456789101112131415161718 Name 11 Na Na 12 Mg Mg 13 Al Al 14 Si Si 15 P P 16 S S 17 Cl Cl 18 Ar Ar

5. Sodium Sodium in a paraffinSilvery white

6. Aluminium foil Large roll of Aluminium foil household aluminum foil

7. Aluminium foil Decorative aluminium foils, in bright colors

8. Sulfur Sulfur crystalites at Wai- o-tapu hot springs, New Zealand Sulfur Sulfur crystal

9. Argon Argon is a colourless gas

10. Chlorine yellowish green

11. Electron arrangement Magnesium, Electron arrangement = 2.8.2 shell electron

12. Electron arrangement electron shell Sodium, Electron arrangement = 2.8.1 No.of atom=no.of electron=proton number Remember!

13. Exercises 1 Make the electron arrangement for the following elements a) aluminium, b) phosphorus, c) sulphur, d) chlorine, e) argon, Answer: 2.8.3 Answer: 2.8.5 Answer: 2.8.6 Answer: 2.8.7 Answer: 2.8.8 answer

14. Properties of elements in Period 3 Element of period 3NaMgAlSiPSClAr Proton number1112131415161718 Electron arrangement2.8.12.8.22.8.32.8.42.8.52.8.62.8.72.8.8 Atomic radius (pm)18616014311811010410094 Physical state at room temperature Solid Gas Electronegativity0.91.21.51.82.12.53.0-

15. Trends of changes across Period 3 1.The atomic radius decreases across the period. a) all the elements in the Period 3 have three filled electron shells but the proton number increases by one unit across the period. b) the increases in the number of proton increases the electrostatic forces between the nucleus and the valence electrons. c) the valence electrons are pulled closer to the nucleus, causing the atomic radius to decrease.

16. Trends of changes across Period 3 2.The number of valence electrons increases across the period. a) proton number increases, the number of electrons increases. b) the number of valence electrons increases by 1 from one element to the next across the period.

17. Trends of changes across Period 3 3.The electronegativity increases across the period. Electronegativity is a measurement of the tendency of an element to attract electrons. a)The atomic radius decreases across the period. b)The proton number increases across the period. c)It will causes an increases in the force of attraction of the nucleus.

18. Trends of changes across Period 3 4. Melting points and boiling points increase from the left of the period to the middle of the period and then decrease again. a) Sodium, magnesium and aluminium are metals with strong metallic bonds between the metal atoms. Hence they have high melting and boiling points. b) Silicon has very high melting and boiling point. It has strong covalent bonds between atoms. What about melting and boiling points phosphorus, sulphur, chlorine and argon?

19. Trends of changes across Period 3 5. Oxide of the elements a)Elements on the left of the period, which are metals, form metal oxides. The metal oxides are usually basic oxides. b)Basic oxides react with acids to form salts and water. Example: MgO(s) + H 2 SO 4 (aq)MgSO 4 (aq) + H 2 o(l) c)Elements on the right of the period are non-metals. Non-metallic oxides are acidic oxides.

20. Acid-base properties of oxides of elements in Period 3 Na 2 OMgOCl 2 O 7 SO 2 P 4 O 10 SiO 2 Al 2 O 3 Across Period 3 Basic oxides Amphoteric oxide Acidic oxides *amphoteric oxide is one that shows some acidic and some basic properties

21. Think! What do you think will happen across the period 2 -Atomic radius -Number of valence electrons -Electronegativity -Oxides of the elements

22. Summary of trends of changes across the period The proton number increases by one unit from one element to the next element All the atoms of the elements have three shells occupied with electrons The number of valence electrons in each atom increases from 1 to 8 All the elements exist as solid except chlorine and argon which are gases The atomic radius of elements decreases. This due to the increasing nuclei attraction on the valence electrons

23. ACTIVITY Work in 5 group members. Try to find the uses of semi-metals in industry. Do a folio ( refer your Chemistry practical book)

24. Exercises 2 Which of the following elements form amphoteric oxides? A.SiliconSilicon B.CarbonCarbon C.AluminiumAluminium D.PhosphorusPhosphorus

25. Exercises 2 2. ElementXYZ Proton number121517 The above table shows the proton numbers of three elements represent by X,Y,Z. Which of the following statements is true? A.The atomic radius decreases in the order X>Y>ZThe atomic radius decreases in the order X>Y>Z B.The electronegativity decreases in the order X>Y>ZThe electronegativity decreases in the order X>Y>Z C.All the elements exist as diatomic moleculesAll the elements exist as diatomic molecules D.X,Y,Z are non-conductors of electricityX,Y,Z are non-conductors of electricity

26. Yess!! You’ve got the answer… QUESTION 1 QUESTION 2

27. Sorry!! You’re wrong… QUESTION 1 QUESTION 2