Comparative chemistry of group 16 part 1

for undergraduate students

1. 4.2 Comparative Chemistry of Group 16 Part-1 Dr Sakina.Z.Bootwala Wilson College 1

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3. Polonium ( Po) atomic number 84. A rare and highly radioactive metal with no stable isotopes. polonium  is chemically similar to selenium and tellurium, though its metallic character resembles that of its horizontal neighbours in the periodic table: thallium, lead, and bismuth. Polonium was discovered in 1898 by Marie and  Pierre Curie ,  Polonium has few applications, and those are related to its radioactivity: heaters in space probes, antistatic devices, sources of neutrons and alpha particles. 3

4. Livermorium  ( Lv ) synthetic chemical element  and has an atomic number of 116. extremely radioactive element The element is named after the Lawrence Livermore National Laboratory , California  The name was adopted by IUPAC on May 30, 2012.  Four isotopes of livermorium are known, with mass numbers between 290 - 293 the longest-lived among them is livermorium-293 with a half-life of about 60 milliseconds. 4

5. Electronic Configuration of Group 16 Elements 5 Element Atomic number Atomic Electron Configuration Inner Shells Penultimate shell (n-1) Valance shell ns 2 np 4 Oxygen (O) 8 [He ] 2s 2  2p 4 Sulphur (S) 16 [Ne ] 3s 2  3p 4 Selenium (Se) 34 [ Ar ] 3d 10 4s 2  4p 4 Tellurium (Te) 52 [Kr ] 4d 10   5s 2  5p 4 Polonium (Po) 84 [ Xe ] 4f 14  5d 10   6s 2  6p 4 Livermorium  ( Lv ) 116 [ Rn ] 5f 14 6d 10 7s 2 7p 4

6. Group 16 elements Oxygen, Sulphur , Selenium, Tellurium, and Polonium are often called the Chalcogens . The name derives from the Greek word chalcos meaning ‘ ore formers’ as extensive number of metal ores are found in the earth's crust as sulfides or oxides 6

7. Physical properties : Atomic size, atomic volume, density & Melting and boiling point Atomic radii, atomic volume , density & Melting and boiling point are expected to increase gradually with increase in atomic number from oxygen to tellurium. polonium has low MP& BP . The huge distinction between the melting and boiling points of oxygen(MP:54K,BP:90K) and sulphur (MP:386K,BP:718K) is that oxygen exists as a diatomic atom while sulphur exists as polyatomic particle 7

8. Physical properties : Ionization energy, electropositive and electronegative character Ionization energy decreases with increase in atomic radii from O to Po Electropositive character increases and electronegative character decreases down the group. which indicates metallic character increases from O to Po. 8

9. Physical properties : Electron Gain Enthalpy: The electron gain enthalpy decreases with increase in size of the central atom moving down the group . Oxygen molecule has a less negative electron gain enthalpy than sulphur . From S to Po electron gain enthalpy becomes less negative because of increase in atomic size 9

10. Physical properties : Metallic and non-metallic character : Metallic character increases from O to Te. O and S shows strong non-metallic character than Se & Te. Po is distinctly a metal .(radioactive and short lived).. 10

11. Oxidation states: The oxidation state of elements is defined as the number of electrons gained or lost to form a bond and its sign is the indication of ionic charge on the element. Group 16, electronic configuration is ns 2 np 4 ,and hence it has 6 electrons in its outer most shell ,these elements gain or share two electrons to attain noble gas configuration. Group 16 elements show -2 ( by accepting 2 electrons), +2, +4, and +6 (by sharing electrons/ losing electrons ) oxidation state. 11

12. Oxidation states: Oxygen is the most electronegative element after fluorine . The difference in electronegativity between metals and oxygen is generally very high. Thus ionic bond is formed when the difference in electronegativity of any two elements is very high. Thus , metals and oxygen combine to form a metal oxide with oxygen attaining O 2-  form, so the oxidation state of oxygen is mostly (-2). 12

13. Oxidation states: Electronegativity of chalcogens decreases down the group. sulphur, selenium, and tellurium react with a more electropositive element of group 1, 2 and lanthanides to form sulphides, selenides , and tellurides . These compounds are the most stable and can be denoted as S 2- , Se 2- , and Te 2- . The electronegativity difference between the compounds (sulphides, selenides , and tellurides ) shows that they are on the borderline of 50% ionic and 50% covalent characters 13

14. Oxidation states: O does exhibit other oxidation states like -1 in H 2 O 2 , positive oxidation state like +2, +1 when it combines with more electronegative element eg . OF 2 , O 2 F 2. O has small atomic size, high ionization potential, and high electronegativity , unavailability of d orbital, and stable -2 oxidation state, thus it is different from other elements. 14

15. Oxidation states: S, Se, and Te show -2 oxidation states, Po show +2 oxidation state. Due to availability of d orbital S, Se, Te, and Po show +4 oxidation states when four unpaired electrons are involved in bonding and +6 oxidation states when all 6 valance electrons are involved in bonding. The compounds of fluorine shows +6 state. Element Oxidation States    8 O    Oxygen   -2,-1,+1,+2    16 S   Sulphur   -2,+2,+4,+6    34 Se   Selenium   -2,+2,+4,+6     52 Te   Tellurium   -2,+2,+4,+6     84 Po   Polonium   +2,+4    15