S & p block elements

The elements in which the valence electron enters the s orbital are called s block elements.
The elements in which the valence electron enters the p orbital are called p block elements.

1. s & p block elements CHAPTER 13 CHEMISTRY XII FDC SIDRA JAVED

2. Atomic Properties of Period 3 Elements Electronic Structure In Period 3 of the Periodic Table, the 3s and 3p orbitals are filling with electrons. Just as a reminder, the shortened versions of the electronic structures for the eight elements are:

3. Sodium Na 1s 2 2s 2 2p 6 3s 1 Or [Ne] 3s 1

4. Magnesium Mg [Ne ] 3s 2

5. Aluminium Al [Ne] 3s 2 3px 1

6. Silicon Si [Ne ] 3s 2 3px 1 3py 1

7. Phosphorous P [Ne ] 3s 2 3px 1 3py 1 3pz 1

8. Sulphur S [Ne] 3s 2 3px 2 3py 1 3pz 1

9. Chlorine Cl [Ne] 3s 2 3px 2 3py 2 3pz 1

10. Argon Ar [Ne] 3s 2 3px 2 3py 2 3pz 2

11. 1. Trends in Atomic Radius All these elements have only 3 shells as they belong to the period no 3. The effective nuclear charge increases from left to right with increase in the atomic number or number of protons in the nucleus. The increased nuclear charge pulls the electrons of the atoms nearer to the nucleus thus the size of the atoms go on decreasing from left to right Ionic radii of positive ions decreases from left to right due to same increase in effective nuclear charge Ionic radii of the negative ions starts from Si to Cl also decreases. Na Mg Al Si P S Cl Ar Atomic Radius 1.54 1.36 1.18 1.11 1.06 1.02 0.99 0.98 Ionic Radius 0.95 0.65 0.50 0.41 0.34 0.29 0.26 -

12. Thus in any period the alkali metals (that are present at the extreme left of the periodic table) have the largest size while the halogens ( that are present at the extreme right excluding VIII group) have the smallest size. The size of inert gas atom is larger than that of the preceding halogen atom. 1. Trends in Atomic Radius

13. 2. Trends in First Ionization Energy Energy required to remove the most loosely held electron from 1 mole of gaseous atoms to produce 1 mole of gaseous (+1) ion is called First Ionization Energy X 9  X g + + 1e - First Ionization energy depends upon following factors; Atomic size Nuclear charge Sheilding effect Nature of orbita l

14. Ionization energy increases from left to right due to successive increase in nuclear charge and decrease in atomic size. Certain elements show irregular trends e.g. Mg and P have higher Ionization energy values than Al and S Reason: In case of Mg ([Ne 3s 2 ) it is more difficult to remove an electron from the completely filled 3s orbital while in case of Al ([Ne 3s 2 3px 1 ) it is easier to remove the same from partially filled 3p orbital. Same is the case with P ([Ne 3s 2 3p 3 ) and S ([Ne 3s 2 3p 4 ) Period 3 Na Mg Al SI P S Cl Ar First Ionization Energies (KJ/ mol ) 496 738 578 786 1012 1000 1251 1520

15. 3. Trends in Electronegativity Electronegativity is a measure of the tendency of an atom to attract a bonding pair of electrons The P auling scale is the most commonly used Fluorine (the most electronegative element) is assigned as a value of 4.0 and values range down to Caesium and Francium which are the least electronegative elements at 0.7 In period 3, E.N values increase from left to right. Notice that Argon is not included since it does not form covalent bonds.

16. Increase in E.N values of period 3 can be explained as follows: On moving from left to right in a period there is a decrease in the size of the atoms. Smaller atoms have greater tendency to attract the electrons towards themselves i.e. smaller atoms have higher E.N values On moving from left to right in a period there is an increase of ionization energy and electron affinity of the elements. The atoms of the elements which have higher value of Ionization energies and electron affinities also have higher electronegativities. 3. Trends in Electronegativity

17. Physical Properties of Period 3 elements Structures of the elements T he structures of elements change as you go across the period. Na, Mg, Al  Metallic solids Si  Giant Covalent solid P, S, Cl , Ar  Molecular solids

18. Three Metallic Structures – Na, Mg, Al In Na, only one electron per atom is involved in metallic bond i.e. 3s 1 electron. In Mg, both of its outer electrons i.e. 3s 2 are involved and in Al all three valence electrons i.e. 3s 2 3p 1 are involved. The coordination number of atoms in the metal crystal is also different in these metals. Na is 8 coordinated i.e. each Na is touched by only 8 other atoms Mg and Al are 12 Coordinated This is a more efficient way to pack atoms leading to less wasted space in the metal structures and to stronger bonding. Sodium Aluminium Magnesium

19. A Giant C ovalent Structure – Si Silicon has a giant covalent structure just like diamond. A tiny part of the structure looks like this:

20. Four Simple Molecular Structures – P, S, Cl , Ar The structures of P (i.e. white, red etc.) and S (i.e. rhombic or monoclinic etc.) vary depending on the type of P or S . The atoms in each of these molecules are held together by covalent bonds. A rgon is a monoatomic molecule . In the liquid or solid state, the molecules are held close to each other by Van der Waals dispersion forces.

21. 4. Trends in Electrical Conductivity Sodium, magnesium and aluminium are all good conductors of electricity. These Metals conduct electricity because the delocalised electrons (the "sea of electrons") are free to move throughout the solid or the liquid metal. Conductivity increases as you go from sodium to magnesium to aluminium as they have more free electrons Silicon is a semiconductor. None of the rest conduct electricity because they are simple molecular substances. There are no electrons free to move around .

22. 5. Trends in Melting and Boiling Points The Melting and Boiling point values tells us about the strength of forces present in the atoms, ions and molecules. These values are according to the binding energies present in elements. Left to right in a period, the MP and BP increase up to group IVA and then decreases from group VA to VIIIA .

23. 5. Trend in Melting and Boiling Point Trend in MP and BP can be explained as follows: The MP and BP are governed entirely by the size of the molecules and intermolecular forces i.e. binding electrons present in the shell. The MP and BP are high up to group IVA because these elements contain increasing number of binding electron from I to IV and also have giant covalent structure. The MP and BP are lo from P to Ar because these elements exist in the form of diatomic molecules and have weak intermolecular forces up to Ar

24. Chemical Reactions of Period 3 Elements

25. Reaction with water a . Sodium Sodium has very exothermic reaction with cold water producing hydrogen gas and a colorless solution of sodium hydroxide. 2Na + 2H 2 O 2NaOH + H 2

26. b. Magnesium Magnesium has a very mild reaction with cold water, but burns in steam. A very clean coil of magnesium dropped into cold water eventually gets covered in small bubbles of hydrogen which float it to the surface. Magnesium hydroxide is formed as a very thin layer on the magnesium and this tends to stop the reaction. Mg + 2H 2 O(Cold) Mg(OH) 2 + H 2 Magnesium burns in steam with its typical white flame to produce white magnesium oxide and hydrogen. Mg + 2H 2 O(Steam) Mg(OH) 2 + H 2 Reaction with water

27. Reaction with water c. Aluminium Aluminium powder heated in steam produces hydrogen and aluminium oxide. The reaction is relatively slow because of the strong aluminium oxide layer on the metal, and the build-up of even more oxide during the reaction. 2Al + 3H 2 O(Steam) Al 2 O 3 + 3H 2

28. Reaction with water d. Silicon Monocrystalline silicon is fairly unreactive. Most sources suggest that its form of silicon will react with steam at red heat to produce silicon dioxide and hydrogen Si + 2H 2 O(Steam ) red hot SiO 2 + 2H 2 It is possible to make reactive form of silicon which will react with cold water to produce the same products. e. Phosphorus and Sulphur These have no reaction with the water.

29. f. Chlorine Chlorine dissolves in water to some extent to give a green solution. A reversible reaction takes place to produce a mixture of hydrochloric acid and chlorous (I) acid ( hypochlorous acid). Cl 2 + H 2 O HCl + HOCl In the presence of sunlight, the chloric(I) acid slowly decomposes to produce more hydrochloric acid, releasing oxygen gas. 2HOCl 2HCl + O 2 The over all change be expressed as: 2Cl 2 + 2H 2 O 4HCl + O 2 g. Argon These have no reaction with the water. Reaction with water

30. Reaction with Oxygen a. Sodium Sodium burns in oxygen with an orange flame to produce a white solid mixture of sodium oxide and sodium peroxide. For the simple oxide: 4Na + O 2 2Na 2 O For the peroxide 2Na + O 2 Na 2 O 2

31. b. Magnesium Magnesium burns in oxygen with an intense white flame to give while solid of Magnesium oxide. : 2Mg + O 2 2MgO Note: If Magnesium burns in air rather than in pure Oxygen, it also reacts with the Nitrogen in the air forming a mixture of Magnesium oxide and Magnesium nitride. 2Mg + N 2 Mg 3 N 2 c. Silicon Silicon will burn in oxygen if heated strongly. Silicon dioxide is produced. Si + O 2 SiO 2 Reaction with Oxygen

32. c. Phosphorus White phosphorus catches fire spontaneously in air, burning with a white flame and producing clouds of white smoke - a mixture of phosphorus (III) oxide and phosphorus (V) oxide. The proportions of these depend on the amount of oxygen available. In an excess of oxygen, the product will be almost entirely phosphorus (V) oxide. For the phosphorus (III) oxide: P 4 + 3O 2 2P 2 O 3 For the phosphorus (V) oxide: P 4 + 5O 2 2P 2 O 5 Reaction with Oxygen

33. Properties of the Oxides of Elements in Period 3

34. Reaction with Chlorine a. Sodium Sodium burns in chlorine with a bright orange flame. White solid sodium chloride is produced. 2Na+Cl 2 2NaCl b. Magnesium Magnesium burns with its usual intense white flame to give white magnesium chloride. Mg+Cl 2 MgCl 2

35. Reaction with Chlorine c. Aluminium Aluminium is often reacted with chlorine by passing dry chlorine over aluminium foil heated in a long tube. The aluminium burns in the stream of chlorine to produce very pale yellow aluminium chloride. This sublimes (turns straight from solid to vapour and back again) and collects further down the tube where it is cooler. 2Al+3Cl 2 2AlCl 3

36. Reaction with Chlorine d. Silicon When chlorine is passed over silicon powder heated in a tube, it reacts to produce silicon tetrachloride. This is a colorless liquid which vaporizes and can be condensed further along the apparatus. Si+2Cl 2 SiCl 4

37. Reaction with Chlorine e. Phosphorus White phosphorus burns in chlorine to produce a mixture of two chlorides, phosphorus(III) chloride and phosphorus(V) chloride (phosphorus trichloride and phosphorus pentachloride). Phosphorus(III) chloride is a colorless fuming liquid. P 4 + 6Cl 2 4PCl 3 Phosphorus(V) chloride is an off-white (going towards yellow) solid. P 4 + 10Cl 2 4PCl 5

38. Reaction with Chlorine f. Sulphur When a stream of chlorine is passed over some heated sulphur, it reacts to form an orange, evil-smelling liquid, disulphur dichloride, S 2 Cl 2 . 2S + Cl 2 S 2 Cl 2 g. Chlorine It obviously doesn't make sense to talk about chlorine reacting with itself. h. Argon Argon doesn't react with chlorine.

39. End of lesson [email protected]