The Periodic Table

1. The Periodic Table by Mr Victor Lee 30 Sep 2000 ? Click on the slide to proceed

2. Periodic Table The Periodic Table is a way of classifying elements. The elements in the periodic table are arranged horizontally, in increasing order of their atomic number.

3. Structure of the Periodic Table The Vertical Column = Group The Horizontal Row = Periods

4. The GROUP A vertical column in the periodic table is called a group. There are 8 Groups : I, II, III, IV, V, VI, VII and VIII. Transition Metals are grouped between Group II and III. They have no group numbers.

5. Group & Valence Electrons The electrons on the outermost shell is called the valence electrons. The no. of valence electrons = group number. Elements from the same group form ions with similar formulae, form compounds with similar formulae and undergo similar chemical reactions.

6. The PERIOD A horizontal row in the Periodic Table is called a period. Each period with the exception of the first begins with metals on the left-hand side and ends with non-metals on the right-hand side. In the first period there are only two elements : hydrogen and helium.

7. Period & Electron Shells The period number = the number of electronic shells the elements possess. For example, Sodium in the third period, would have 3 electronic shells. Elements in the same period have the same number of electronic shells.

8. Group I � alkali metals Valency = 1 Lithium, Sodium, Potassium Physical Properties Soft metals : Na can be cut with razor blade Low density : Na, density = 0.97 glcm3 => Sodium can float on water. Low m.p. and b.p. : Na, m.p. = 98?C

9. Group I � alkali metals all conduct electricity. all very reactive with the air and water. react with water to form an alkali & hydrogen: alkali metal + water ? alkali + hydrogen gas 2Na + H2O ? 2NaOH + H2

10. Group I � alkali metals burn readily in air to form oxides: alkali metal + oxygen gas ? metallic oxide 4K + O2 ? 2K2O The reactivity of the elements increases down the group (Li <Na < K < Rb < Cs).

11. Why does reactivty increases ? down the Group I ? Going down the group, the number of electrons increases and thus the number of electron shells and the atom size increases. The valence electron being further from the nucleus will experience weaker attraction force from the nucleus, thus easier to escape. Since reactivity of metals depends on the ability to lose its valence electrons, the reactivity increases down the Group I.

12. Group VII - Halogens Valency = -1. are non-metals. exist as diatomic molecules. are all volatile => low m.p. & b.p. are non-conductor of electricity. all can dissolve in organic solvents. colouration of the elements becomes darker further down the group.

13. Group VII - Halogens The reactivity of the elements decreases as you go down the group. A more reactive halogen will displace a less reactive one from its salt. 2KI (aq) + Cl2 (g) ? 2KCl (aq) + I2 (g) Observation: Yellow green gas of chlorine will disappear into the colourless solution of potassium iodide to produce a brown solution of Iodine in water, and colourless potassium chloride solution.

14. Why does reactivty decreases ? down the Group VII ? Going down the group, the number of electrons increases and thus the number of electron shells and the atom size increases. The increase in atomic size makes it more difficult for the nucleus to attract an electron to form an ion. Since reactivity depends on the ability to gain an electron to form ion, the reactivity decreases down the group.

15. Why does melting and boiling points increases ? down the Group VII ? Consists of small diatomic covalent molecules held together by strong covalent bonds within each molecules The intermolecular forces of attraction (van der Waals forces) between the covalent molecules are very weak. Since these weak intermolecular forces increases with the size of the molecules, the m.p. & b.p. increases down the group.

16. Group O or VIII � Noble Gas valency = 0 are all non-metals. exist as monatomic gases. Properties: very low m.p. & b.p. which increase down the group; do not conduct electricity very unreactive.

17. Transition Elements high densities : density of iron = 7.9 g/cm3 high m.p. & b.p. : m.p. of iron = 1535?C form coloured compounds iron(II) sulphate is pale green copper (II) sulphate is blue strong hard metals are good catalysts : iron in Haber Process, manufacture ammonia gas variable valencies : Fe2+ & Fe3+

18. Diatomic Diatomic molecules are molecules made up of 2 atoms