The periodic table for grade 9 & 10

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1. THE PERIODIC TABLE

2. Importance of classification of elements Organization and relationship between elements are defined. Properties of elements can be correlated with properties of states of matter.

3. Basis of classification of elements: Early Chemists: based on properties, valencies & metallic and non-metallic nature of elements. The method was discarded since elements behave both as metals and non-metals, shows metallic and non-metallic nature and have variable valency.

4. Dobereiner's law of triads : ’Chemically analogous elements arranged in increasing order of atomic weights formed well marked groups of three called triads in which the atomic weight of the middle element was found to be generally the average of the atomic weights of the other two elements.’

5. Limitations of Dobereiner’s Triads: The identification of new elements made this model obsolete. Newly discovered elements did not fit into the triads. Only a total of 5 Dobereiner’s triads were identified. Even several known elements did not fit into any of the triads.

6. Newlands law of octaves: When the elements are arranged in increasing order of their atomic masses, the properties of the eighth element are like that of the first.

7. L imitations of Newlands ' law of octaves: It was applicable to only lighter elements having atomic masses up to 40, i.e., up to calcium. After calcium, the first and the eighth element did not have similar properties. It failed to leave spaces for undiscovered elements.

8. Mendeleev’s Periodic law : The Physical and Chemical Properties of the elements are periodic functions of their atomic weights.

9. Mendeleev’s contributions: Elements were arranged in increasing order of atomic weights in periods and groups. Elements with similar chemical properties are grouped together. Elements in the same group had the same valency. Gaps were left for undiscovered elements. The properties of the undiscovered elements were predicted. Incorrect atomic weights of some of the arranged elements were corrected.

10. Defects in Mendeleev’s periodic table: Anomalous pairs. Position of isotopes Position of rare earths and actinides

11. Modern Periodic Law: Moseley modified Mendeleev’s periodic law to form the modern periodic law – The physical and chemical properties of elements are the periodic function of their atomic numbers.

12. Periodicity of elements Gradual change in properties is seen with increase in atomic number Periodicity – recurrence in properties are seen in:- Elements belonging to the same subgroup After a difference of 2,8,18 or 32 in atomic numbers due to recurrence of similar valence electronic configuration.

13. Salient Features of modern periodic table 1. The modern periodic table has 7 horizontal rows called 'Period'. Elements of the same period have the same number of electron shells. Electrons in the outermost shell increases progressively for elements of the same period. Period number signifies the number of electron shells. Transition from metallic to non-metallic character. Separation of elements : => Reactive metals: group IA and 2A =>Transition metals: in the middle =>Non - Metals: upper right corner

14. 2.There are 18 vertical columns in the periodic table called ‘Groups’. 2.There are 18 vertical columns in the periodic table called ‘Groups’. Group 1-alkali metals Group 2- alkaline earth metals Group 3- 12 – transition elements Group 13-16 – post transition elements Group 17 –halogens Group 18 – noble / inert gases. Group 1,2,13,14,15,16,17 – normal elements/representative elements. Group number signifies the number of valence electrons of an element. Elements of the same group have the same number of valence electrons hence same valency and similar properties. Number of electron shells increases by one Metallic character increases down a group.

15. Period in a periodic table In the periodic table of the elements, each numbered row is a period. In the periodic table of the elements, elements are arranged in a series of rows (or periods) so that those with similar properties appear in a column. Number of electron shells remain the same from left to right of a period . Valance electrons increases by one from left to right of a period . The non - metallic character increases from left to right of a period .

16. Bridge elements They show similarities in properties diagonally with the period of the next group.

17. Group in a periodic table A group (also known as a family) is a column of elements in the periodic table of the chemical elements. There are 18 numbered groups in the periodic table, but the f-block columns (between groups 2 and 3) are not numbered.

18. Property trends – down a sub-group Valence electrons – Remain same Chemical properties - Remain same Metallic character/electro positive character – increases down No. of electron shells increases by one.

19. Group IA elements Group VIIA elements Elements Li, Na, K, rubidium, caseium, francium Fl, Cl, Br, I, astatine Valency 1 valence eˉ => Univalent 7 valence eˉ => univalent Nature Highly – reactive and electropositive ; light & soft metals – can be cut with a knife Highly – reactive and electronegative; Non - metals – some are gaseous, liquid and solid at room temp. Conductivity Good Bad or Non - conductors Reducing / oxi- dizing agents Strong reducing agents Strong oxidizing agents Reaction with Nonmetals Electrovalent compounds are formed Covalent compounds are formed Reaction with ‘H’ Ionic hydrides are formed Covalent hydrides are formed

20. Periodicity Periodicity: occurrence of characteristic properties of elements at definite intervals in the modern periodic table when elements are arranged in the increasing order of their atomic numbers. The cause of periodicity is the recurrence of similar electronic configuration.

21. Atomic radius/size .   Atomic radius: distance between the center of the nucleus and the outermost shell. U nit => A    

22. Factors affecting Atomic radius/size Number of shells increases & atomic size increases Reason – As the No. of shells increases – the distance between the nucleus and the outermost shell increases Nuclear charge increases and atomic size decreases Reason – Nuclear charge increases – the electrons of the outermost shell are attracted with increasing force Nuclear charge is the positive charge of the atom Nuclear charge is equivalent to the atomic number of the element

23. Trends in atomic size – from left to right of a period Number of shells – Remain the same and Atomic Size – Remains unaffected Nuclear charge – Increases and Atomic size – Decreases In Period 2 – Li – largest atomic Radius In period 2 – F - smallest atomic radius Neon has larger atomic radius as its outermost shell is completely filled The effect of nuclear pull over the valence shell electrons is not seen

24. Trends in atomic size ; down a group Number of shells increases and atomic size increases Nuclear charge increases and atomic size should decrease Atomic radius/size increases down a group

25. Ionization potential . Ionization potential : amount of energy required to remove an electron from the outermost shell of an isolated gaseous atom. Unit => eV

26. Factors affecting – ionization potential Atomic size increases and Ionization potential – Decreases Reason – Atomic size increases and the nuclear attraction on the outer electron - decreases Outer electrons are loosely held Nuclear charge increases and ionization potential – increases Reason – Nuclear charge increases and the nuclear attraction on the outer electron – increases Outer electrons are tightly held

27. Trends in ionization potential Helium has highest ionization potential while caesium has the lowest Metals lose electrons and so have low I.P. compared to non-metals I.P. increases across a period

28. Trends in I.P. – down a group Atomic radius increases and I.P. decreases Nuclear charge – Increases and so I.P. should decrease I.P. decreases down a group

29. Electron Affinity amount of energy released when an atom in the gaseous state accepts an electron to form an anion. Unit is eV

30. Factors affecting electron affinity Atomic size increases and Electron affinity decreases Reason: A small atom takes up electrons more readily than a large atom Because the nucleus has greater attraction on the electrons Nuclear charge increases and electron affinity increases Nuclear charge increases: Similarly increases the tendency of atom to accept electrons

31. Trends in electron affinity – across a period – from left – right Atomic radius decreases and electron affinity increases Nuclear charge increases and electron affinity increases Neon has electron affinity zero as its outermost shells are filled Electron affinity is highest for halogens group 17 and least for alkali metals group 1 More value of electron affinity more is the electronegativity Electron affinity increases across a period from left to right

32. Trends in electron affinity down a group Atomic radius increases and E.A. decreases Nuclear charge – Increases and so E.A. should decrease E.A. decreases down a group

33. Electro - negativity It is the tendency of an atom to attract itself in the gaseous state accepts an electron to form an anion

34. Factors affecting electro-negativity Atomic size increases and electro-negativity decreases. Nuclear charge increases and electronegativity increases Reasons – same as electron affinity

35. Trends in electro-negativity across a period from left to right Atomic radius decreases and electro-negativity increases Nuclear charge increases and electro-negativity increases Elements with high electronegativity are usually non-metallic Fluorine is the most electronegative element and caesium id the least Noble gases have complete octet and so they do not attract electrons electro-negativity increases across a period from left to right

36. Trends in Electro-negativity down a group Atomic radius increases and electro-negativity decreases Nuclear charge increases and electro-negativity should increase Electro-negativity decreases down a group

37. Features of long form of periodic table 1. 18 vertical columns known as groups. 2. 7 Horizontal rows known as periods.  3. Light metals These are elements of periodic table of group 1 and 2. 4. Heavy metals or Transition metals - These are elements of periodic table of group 3, 4, 5, 6, 7, 8, 9, 10, 11 and 12.     5. Non-Metals These are elements of periodic table of group 13, 14, 15, 16 and 17.  6. Zero group These are elements of periodic table of group 18.

38. Metallic and non metallic character - term Metallic character electro positive Non - Metallic character In terms of electron losing property – an atom is said to be a – Metal , if it loses one or more electrons when supplied with energy. In terms of electron gaining property – an atom is said to be a – Metal , if it gains one or more electrons when supplied with energy.

39. Factors affecting metallic and non- metallic character Atomic radius increases and metallic character increases , nonmetallic character decreases. I.P. increases and metallic character decreases , nonmetallic character increases. Metallic atoms are present on the left side of the periodic table have large atomic radius and low I.P. value and lend to lose – electrons Non - Metallic atoms are present on the right side of the periodic table have small atomic radius and high I.P. value and lend to gain – electrons Metals are good reducing agents Non – Metals are good oxidizing agents

40. Trends in character – across a period from left to right Atomic radius decreases and metallic character decreases ; non – metallic character increases I.P. increases and metallic character decreases ; non – metallic character increases Metallic character decreases across a period ; Non – metallic character increases across a period

41. Trends a character down a group Atomic radius increases and metallic character increases ; non – metallic character decreases I.P. decreases and metallic character increases ; non – metallic character decreases Metallic character increases across a period ; Non – metallic character decreases across a period

42. Physical properties - density and melting point Across a period – density and & melting points – increase gradually

43. Physical properties - density and melting point and boiling point Down a group density increases gradually & m.p & b.p. of elements decreases gradually

44. Chemical properties – periodicity in properties of compounds of elements Characteristics Varies across a period Varies down a group Oxides Strongly basic to strongly acidic Acidic to Basic Hydroxides Strongly basic to Amphoteric Less basic to Strongly basic Oxy-acids Weak oxy-acids to Strong oxy-acids Strong oxy-acids to Weak oxy-acids Hydrides Strongly basic to strongly acidic Less Acidic to More Acidic

45. Stable and unstable elements Elements arranged in the periodic table having n/p (neutrons/protons) ratio around 1 are stable Elements arranged in the periodic table having n/p (neutrons/protons) ratio above 1.5 are unstable stable E.g. – light – Na ; heavy – uranium.

46. Modern Periodic Table

47. About There are 18 vertical columns in the periodic table. Each column is called a group. All elements in a group have similar chemical and physical properties because they have the same number of outer electrons.  In periodic table elements are arranged in a series of rows. Elements of the same period have the same number of electron shells.

48. Modern Periodic Law The properties of elements are the periodic function of their atomic number i.e. number of protons.

49. Position of Elements in the Periodic Table

50. Location of Metals, Non-metals, Metalloids and Noble Gases are as follows: Elements on the left and middle are  Metals  Elements on the right are  Non-metals   Metalloids  form the narrow stair-step area between metals and non-metals The last group (18) to the right are  Noble gases

51. Periodic Table Chart The  Periodic Table  organizes the elements according to their similar chemical and physical properties. The Table has rows and columns. The vertical columns in the periodic table represent  Groups . The horizontal rows in table represents  Periods .

52. Determine the period number of elements All the elements in a period have the same number of atomic orbitals. For example, every element in the top row (the first period) has one orbital for its electrons. All the elements in the second row (the second period) have two orbitals for their electrons.

53. Determine the group number of elements The group number is an identifier used to describe the column of the standard periodic table in which the element appears. Groups 1-2 (except hydrogen) and 13-18 are termed main group elements. Groups 3-11 are termed transition elements. Electronic configuration of Sodium is 2, 8, 1. So the number of group is 1

54. Occurrence of alkali earth metals Alkaline earth metals are obtained in the form of their ore in earth's crust. Of the alkaline earth metals calcium and magnesium rank fifth and sixth in abundance respectively, in earth crust. Beryllium is rare and radium is rarest of all.

55. CHARACTERISTICS Alkali metals are highly reactive elements. They are soft, have low density, low melting point, low boiling point, give characteristic color to the flame, are strongly electro-positive character. They react with water liberating H2 and react with acids replacing hydrogen.

56. NOBLE GASES Noble gases are the gases present in group  VIIIA(18)  which has its outer shell completely fill. Some of the common properties of noble gases are: Almost Non-reactive  High ionization energies  Very low electronegativities  Low boiling points (all monatomic gases at room temperature)  No color, odor, or flavor under ordinary conditions  Non-flammable  At low pressure, they will conduct electricity