1. Periodic Table: The systematic arrangement of elements in different groups and periods according to their property is called periodic table.
2. Mendeleev’s Periodic Law: It states “Physical and chemical properties of elements are periodic function of their atomic weights.”
3. Advantage of Mendeleev’s periodic table:
i) Systematic study of the elements for 1st time.
ii) Prediction of new elements.
iii) Correction of certain doubtful atomic weights.
4. Draw backs mendeleev’s Periodic Table:
i) The position of hydrogen is not properly defined.
ii) Alkali and other metal like gold, silver, copper were in same group.
iii) Elements with more atomic weights come before less atomic weight element which violates law.
iv) No place for lanthanides and actinides.
5. Modern periodic law:
It state, “The physical and chemical properties of elements are periodic function of their atomic number.”
6. Characteristics of modern periodic table:
i. There are seven horizontal raws called period and eight groups. Group from I to VII has two sub groups A and B group VIII has three sub group and there is one zero group.
ii. The elements of group IB to VIIB are called transition element. Transition element are also called ‘d’ block element.
iii. Lanthanides and Actinides are two series of inner transition element with 14 elements each.
iv. Element belonging to group zero, He, Ne, Kr, Xe and Rn are called Nobel or inert gases as they do not take part in chemical reaction.
7. Some characteristics of group:
i. All elements in group have same number of valence electrons. Their valency is also same.
ii. Size of atoms increases on going top to bottom in group.
iii. The ionization energy of an atom decreases on moving from top to bottom in group.
iv. Electro negativity (tendency to attract electron) decreases ongoing top to bottom.
- Electro positivity (tendency to lose electron) increases on moving from top to bottom.
- Chemical reactivity increases on metal while going top to bottom but reactivity decreases from non-metals on going down.
REASONABLE FACTS
1. Lithium and sodium are kept in group IA.
Ans- Lithium and sodium are kept in group IA because both contain one valence electron and both of them react with water to produce corresponding alkali and hydrogen gas.
2. Sodium is more reactive than lithium.
Ans- Sodium is more reactive than lithium because the atomic size of sodium atom is larger than that of lithium atom so that sodium can easily lose its valence electron during a chemical reaction.
3. Sodium is a metal and chlorine is a non-metal.
Ans- Since sodium has a capacity to donate electron as well as possess metallic lusture, ductility and is malleable and also can conduct electricity but the chlorine can accepts electrons and cannot conduct electricity as well as it exist in gaseous state with no metallic lusture, ductility and malleable. Hence, sodium is a metal and chlorine is a non-metal.
4. Chlorine is more reactive than bromine.
Ans- Chlorine is more reactive than bromine because the atomic size of chlorine atom is smaller than that of bromine atom so that chlorine can easily gain its valence electron during a chemical reaction as the nuclear attraction is also greater on the vaience shell of chlorine.
5. Potassium is more reactive than sodium.
Ans- Postassium is more reactive than sodium because the atomic size of potassium atom is larger than that of sodium atom so that the valence electron of potassium fan more easily be taken by other reacting atoms as compared to that of sodium.
6. The valencies of both sodium and chlorine are one but they are kept in group IA and VIIA resp.
Ans- Sodium has one valence electron and chlorine has seven valence electrons. As group no. is equal to the no. of valence electrons, sodium and chlorine are kept in group IA and VIIA resp.
7. Sodium and chlorine are reactive in a chemical reaction.
Ans- Sodium has one electron in the outermost shell and can lose it easily but chlorine has seven electrons in its outermost shell and can gain one electron easily. So sodium and chlorine are reactive in a chemical reaction.
8. Fluorine is more reactive than chlorine. (Both are of group VIIA)
Ans- Fluorine is more reactive than chlorine because Fluorine can attract the electron more easily due to its smaller atomic size.
9. Chlorine is more reactive than nitrogen.
Ans- As chlorine needs one electron to be fulfilled but nitrogen needs three electrons to complete its outermost orbit. So it is easy to gain one electron than three electrons. Hence chlorine is more reactive than nitrogen.
10. Calcium is more reactive than magnesium.
Ans- Calcium can lose two valence electrons more easily due to its larger atomic size and the electron losing power increase in the atomic size. So calcium is more reactive than magnesium.
11. The valency of calcium is 2.
Ans- As calcium can lose its two valence electrons to complete its outermost orbit or to get octet configuration and so valency is equal to no. of losing or gaining or sharing electrons. Hence, the valency of Calcium is 2.
12. Calcium is smaller than potassium.
Ans- Due to the more nuclear charge to pull outer electrons more strongly, calcium is smaller than potassium
13. Potassium is more reactive than calcium although both lie in the same period.
Ans- Atomic no. of calcium is greater than atomic no. of postassium so nuclear charge of calcium is more than potassium. Due to greater nuclear charge, valence electrons of calcium do not readily involved in chemical reaction than potassium. Hence, the valence electrons of potassium are easily lost out so it is more reactive than calcium.
14. Argon atom can exist freely in nature.
Ans- The outermost orbit of Argon atom consists of eight electrons or the valence shell or argon is fulfilled by having eight electrons. Due to this, it does not take part in chemical reaction. Hence argon atom can exist freely in nature.
15. All the elements of a group have similar chemical properties.
Ans- Since, the chemical properties of elements depends upon valence electrons and due to the presence of same no. of valence electron in a group, the elements have similar chemical properties in a group.
16. The reactivity of group I elements
Ans- The reactivity of group I elements increases as we go down in the modern periodic table because of
– Increasing atomic radius
– Decreasing ionization potential
– Decreasing nuclear attraction towards outermost electrons
17. Elements of group IA, IIA, IIIA are more reactive as we go down in the group.
Ans- Elements of group IA, IIA, IIIA are more reactive as we go down in the group due to their increasing radius and decreasing lionization potential and can lose the electrons to be stable easily.
18. Elements of group VA, VIA, VIIA are less reactive as we go down in the group of the periodic table.
Ans- While going down the group VA, VIA, VIIA, there is increase in the radius which causes the less attracting capacity between proton and electron. So it is difficult for the elements of these groups to gain electrons. Hence such groups of elements are chemically less reactive as we go down in the group.
19. The elements of group VA, VIA and VIIA are electro-negative charge in periodic table.
Ans- The elements of group V,VIA and VIIA complete their valence shell by accepting electrons from other atoms and becomes octet. Hence, the elements of groups VA, VIA and VIIA are electro-negative charge in periodic table.
20. Neon and argon are inert or inactive gases.
Ans- Neon and argon are inert or inactive gases because their outermost orbit consists 8 electrons having stable electronic configuration so that they do not take part in chemical reaction.
21. Noble gases (He, Ne, Ar, and Kr etc.) are also represented as the inert gases.
Ans- Noble gases are also called as inert and non-reactive gases because their outermost shells are completely fulfilled.
They are placed in the extreme right side of the modern periodic table in the zero groups.
22. Na and K are called alkali metals.
Ans- Na and K are called alkali metals because they react with water to form an alkali.
23. Though atomic no. of carbon is 6 and silicon is 14 resp., they are placed in same group IVA.
Ans- Though atomic no. of carbon is 6 and silicon is 14 resp., they are placed in same group IVA because they have four valence electrons in the outermost shell so they can either lose or gain electrons equally.
24. The reactivity of group VA elements decreases as we go down the group.
Ans- Atomic size goes on increasing going down in a group which results in the decrement of effective unclear charge of the elements and due to massive electronic charge at the valence shell they do not allow any atoms to approach towards. So the reactivity of group VA elements (valence=3) decreases as we go down in the group.
25. Chlorine is placed in p-block element in the periodic table.
Ans- Chlorine is placed in p-block element in the periodic table because the last electron of chlorine enters to p-sub shell.
26. Atomic weight of Argon is greater than that of potassium but Argon comes before than Potassium in the periodic table.
Ans- Atomic weight of Argon is greater than that of potassium but Argon comes before than Potassium in the periodic table because of greater atomic no. of potassium. (i.e.at. no. of Ar=18 and at. No. of K=19).
27. The position of hydrogen in not satisfactory in Mendeleev’s periodic table.
Ans- It is said that the position of isotopes is not clear in Mendeleev’s periodic table because the elements are not classified on the basis of atomic weights in the periodic table.
28. It is said that the position of isotopes is not clear in Mendeleev’s periodic table.
Ans- It is said that the position of isotopes is not clear in Mendeleev’s periodic table because the elements are not classified on the basis of atomic weights in the periodic table.
29. The isotopes of every element are properly placed in modern periodic table.
Ans- In modern periodic table, all the isotopes of every element are kept in same position of the element so it is considered that the isotopes of every element are properly placed in it.
30. In modern periodic table, hydrogen is placed in group IA of alkali metals and VIIA of
halogen.
Ans.-Hydrogen resembles both alkali metals and halogens. So in modern periodic table,
Hydrogen resembles both alkali metals and halogens. So in modern periodic table, hydrogen is placed in group IA of alkali metals and VIIA of halogen.
31. the position of hydrogen is still controversial.
Ans- In modern periodic table, hydrogen is placed in group IA of alkali metals and VIIA of halogen. Since, the same element is placed in two different groups, the position of hydrogen is not satisfactory, Hence, the position of hydrogen is still controversial.
32. Though hydrogen is a non-metal, it is placed with alkali metals.
Ans-As hydrogen and alkali have one electron in the outermost orbit and can lose that electron to form monovalent cation and are also collected at cathode during the electrolysis process, it is placed with alkali metals though it is a non-metal.
33. Group IA elements are alkali metal.
Ans- Group IA elements are alkali metal because they reacts with water to form an alkali except hydrogen.
34. Alkali metals are highly reactive.
Ans- Since the alkali metals have single valence electron so they can easily lose the electron to achieve an octet state. Hence, they can readily participate in chemical reaction which proves that they are highly reactive.
35. Hydrogen is placed with halogens (Group VIIA)
Ans- Hydrogen is placed with holagens (group VIIA) because of the following reasons:
– Both hydrogen and halogens have one electron less than the nearest noble gas.
– Both are capable of gaining one electron to have stable state.
– Both are diatomic at room temperature such as H2, F2, CL2, Br2 and l2.
36. Lanthanides and actinides are placed at different positions in the periodic table.
Ans- Since Lanthanides and actinides are rare and artificial elements respectively and also have similar properties to the transitional elements and are kept in f-block because of the preferential filling of 4f and 5f sub-orbital’s. Hence they are placed separately below the transitional elements in f-block of modern periodic table.
37. Hydrogen is placed along with metals.
Ans-Hydrogen is placed along with metals due to the following reasons.
– Hydrogen contains only one electron in its outermost orbit like metals.
– Hydrogen forms singly charged electron by losing outermost electron.
38. Atomic size of Aluminium is smaller than that of Sodium.
Ans- Atomic size of Aluminum is smaller than that of sodium because the nuclear charge is more in aluminum than that of sodium. Similarly, the atomic radius is also decreased due to the increment of nuclear charge that attracts electrons in the outermost orbit with increasing force.
39. Sodium is more reactive than hydrogen.
Ans- Sodium is more reactive than hydrogen because atomic size of sodium is larger than that of hydrogen and ionization potential of sodium is less than that of hydrogen.
40. Be, Mg, Ca, Sr, Ba and Ra are called alkaline earth metals.
Ans- Be, Mg, Ca, Sr, Ba and Ra are called alkaline earth metals because of their oxides from in earth’s surface that reacts with water to produce alkalis.
They are more reactive metals of group IIA having two valence electrons.
41. Group IIA elements are alkaline earth metals.
Ans- Group IIA elements are alkaline earth a metal because they occur feely in nature in the form of oxides which when added in water dissolves and forms alkaline solution.
42. F, Cl, Br, I, Al are called halogens. (all are of group VIIA)
Ans- F, Cl, Br, I, Al are called halogens because they are the members of group VIIA having seven electrons in the valence shell which van react with hydrogen to form acids from which simple salts can be made.
43. Outermost electrons of an aton are called valence electrons.
Ans- Outermost electrons of an atom are called valence electrons, because the valency of an atom depends on the no. of valence electrons.
44. D- Block elements transition elements show variable valency.
Ans- D- Block elements transition elements have valence electrons both in their outermost and second outermost shell so the valence electron belonging to the outermost or both the outermost shell so the valence electron belonging to the outermost or both the outermost and penultimate (second outermost) shell may take part in chemical reaction. So transition elements show variable valency.
45. The concept of sub-orbital electronic configuration was developed.
Ans- Since the 2n2 rule of electronic configuration could not include the electronic configuration of all the elements; the concept of sub-shell electronic configuration was introduced.
The sub-shells are s, p, d and f which can fill in up to 2, 6, 10 and 14 electrons resp.
