ICSE Class 10 Chemistry Chapter 01 Periodic Table

Chapter 1: Periodic Properties and Variations of Properties - Physical and Chemical

Important Points to Remember

1. Several attempts were made to classify elements, to arrange them systematically on the basis of their physical and chemical properties.

2. Dobereiner's Triads: According to this, the elements were placed in a group of three called triads. The atomic weight of middle element is the arithmetic mean of the other two. For example

This classification was discarded because many elements could not find their positions in the triad.

3. Newland's Octave Law: Like eight notes of an octave of music, the eighth element starting from one is a kind of repetition of the first element. However, this method of classification was discarded since it failed to accommodate heavier elements and there was no space left for the elements which were discovered later.

4. Mendeleev's Periodic Table: According to Mendeleev, the periodic properties of the elements are the periodic functions of their atomic weights. The arrangement of Mendeleev enabled him to place the elements in the vertical columns and horizontal rows which were called as groups and periods respectively.

5. The elements in the periodic table were arranged in the increasing order of their atomic weights.

6. Mendeleev's Periodic Table has the following main defects:

(a) Position of Isotopes.

(b) Position of Hydrogen.

(c) Position of Lanthanides and Actinides, i.e., rare earth elements.

7. The shortcomings of the Mendeleev's periodic table was overcome by Henry Moseley and he put forward the modern periodic table. In which the elements are arranged in the increasing order of their atomic number.

Modern Periodic Law: The physical and chemical properties of elements are the periodic functions of their atomic numbers.

8. The properties of the elements are repeated after the regular interval or the properties reoccur after the regular interval.

9. Later on Bohr worked on the Moseley's periodic table and Bury in the year 1921 gave the extended form of the periodic table known as the long form of the periodic table.

10. Periodic Table may be defined as the table in which the elements are arranged in the increasing order of their atomic numbers.

11. In the modern periodic table the vertical lines are called as Groups.

12. There are eighteen vertical columns in the periodic table. The order for the arrangement of the group is (from left to right) I A, II A, III B, IV B, V B, VI B, VII B, VIII (undivided), I B, II B, III A, IV A, V A, VI A, VII A and zero. But according to the latest recommendations of IUPAC the groups are numbered from 1 to 18.

13. The elements of group 1, 2, 13, 14, 15, 16 and 17 are called as normal elements or representative elements. These elements have incomplete outermost shell.

14. The elements of group 3, 4, 5, 6, 7, 8, 9, 11 and 12 are known as transition elements.

15. The elements of group 18 or zero group are called as inert gases or noble gases or rare gases as they have stable configuration following the octet rule.

16. Group 1 elements are called as Alkali metals.

17. Group 2 elements are called as Alkaline earth metals.

18. Group 17 elements are called as Halogens. (Salt producers).

19. Elements of group 18 are called as Inert gases or Noble gases.

20. The horizontal rows in the periodic table are called as Periods.

21. There are seven horizontal rows in the periodic table. The number of shells present in an atom determines its period. Elements in period 1 has one shell, elements in period 2 has two shells, elements in period 3 has three shells and so on. For example

22. First period is the shortest period containing only two elements, i.e. Hydrogen and Helium.

23. Second period is a short period containing eight elements (Li, Be, B, C, N, O, F and Ne).

24. Third period is also a short period containing eight elements (Na, Mg, Al, Si, P, S, Cl and Ar).

25. Fourth period is a long period containing eighteen elements.

26. Fifth period is also a long period with eighteen elements.

27. Sixth period is a very long period containing thirty two elements.

28. Seventh period is an incomplete period.

29. In group III B and sixth period, the elements from atomic numbers 57 to 71 are present which are called as Lanthanides

30. In group III B and seventh period, the elements from atomic numbers 89 to 103 are present which are called as Actinides.

31. The elements can be classified as:

1. Representative or Normal elements:

2. Transition elements

3. Inert gases or noble gases

4. Inner transition elements-which includes lanthanides and actinides.

32. The properties which reoccur after a regular interval in periodic table are called as Periodic properties and the phenomenon is called as periodicity.

33. The major cause for the periodicity is the recurrence of similar electronic configuration. In the particular group the valence electrons remains the same and thus the valency is also the same. Hence, the properties are same.

34. Electronic configuration of elements:

(a) Number of Shells

Group: As we move down the group the number of shells increases.

Example: Elements of Group 1 in the periodic table.

Period: As we move across the period the number of shells remain same.

Example: Taking the elements of 2nd period.

(b) Valence electrons: The electrons present in the outermost shell of an atom are called valence electrons.

Group: As we move down the group the number of valence electrons remain the same. Therefore the elements in same period have similar chemical properties.

Period: As we move across the period the number of valence electrons increases.

(c) Valency: The combining capacity of an element is called valency.

Group: As we move down the group the valency remain same as the number of valence electrons are same.

Period: As we move across the period the valency first increases and then decreases and finally becomes zero in case of inert gases.

Example: Elements of 3rd period.

35. According to the Modern Periodic Law the properties of an element depends upon:

(a) Atomic size

(b) Metallic character

(c) Non-metallic character

(d) Ionisation energy

(e) Electron affinity

(f) Electronegativity

(g) Atomic size: It is taken as the distance between the nucleus and the outermost shell of an atom.

Group: As we move down the group atomic size increases as the number of shells increases.

Period: As we move across the period atomic size decreases as the nuclear charge increases but the number of shells remain the same.

(b) Metallic character: It is the tendency to loose electrons easily.

Group: As we move down the group metallic character increases.

Period: As we move across the period metallic character decreases.

(c) Non-metallic character: It is the tendency to gain electrons.

Group: As we move down the group non-metallic character decreases.

Period: As we move across the period non-metallic character increases.

(d) Ionisation energy: It is the energy required to remove an electron from the outermost shell of an atom in its isolated gaseous state.

Group: As we move down the group ionization energy decreases.

Period: As we move across the period ionization energy increases.

- Inert Gases have maximum ionization energy.

- Metals have low ionization energy.

(e) Electron affinity: It is the energy released on adding an electron to the outermost shell of an atom in its isolated gaseous state.

Group: As we move down the group electron affinity decreases.

Period: As we move across the period electron affinity increases.

- Inert Gases have zero electron affinity.

- Non-metals have high electron affinity.

- Halogens have maximum electron affinity in their respective periods.

(f) Electronegativity: It is the tendency on the part of an atom to attract the shared pair of electrons towards its side.

Group: As we move down the group electronegativity decreases.

Period: As we move across the period electronegativity increases.

36. The acidic character of oxides increases as we move across a period.

Example: Na2O, MgO, Al2O3, SiO2, P2O5, SO3, Cl2O7

Basic Amphoteric Acidic Acidic Acidic Acidic

37. The basic character of oxides increases as we move down the Group.

38. The common feature seen at the end of every period is the presence of an inert gas with the complete octet or a stable configuration.

Teacher's Note

Understanding the periodic table helps us predict how substances will react with each other, such as why sodium reacts vigorously with water while argon remains inert in all conditions.

Striking Features of Alkali Metals and Halogens

39. The striking features of alkali metals are:

(i) Highly electropositive in nature.

(ii) Good reducing agents.

(iii) Valency is +1.

(iv) They have low ionization potential.

(v) They form ionic chlorides.

(vi) Good conductors of electricity

(vii) They have largest atomic size in their period

(viii) They react vigorously with dilute acids and cold water to liberate hydrogen. The reactivity decreases on moving down the group.

40. The striking features of halogens are:

(i) Highly electronegative in nature.

(ii) Good oxidizing agents.

(iii) Valency is -1.

(iv) They have high electron affinity.

(v) They undergo ionic bond formation with metals.

(vi) Poor conductors of electricity

(vii) They have smallest size in their period.

(viii) They do not react with dilute acids.

Variation of Periodic Properties Across the Group and the Period

Teacher's Note

When cooking, salt (sodium chloride) behaves so differently from chlorine gas because sodium eagerly donates electrons while chlorine desperately seeks them - opposite ends of the periodic table create opposite chemical personalities.

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