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Q1. There are only 18 elements in the fifth period of the periodic table. Justify this statement.

Solution

The fifth period begins with the filling of 5f orbital and continues till the filling of sixth energy (6s) starts. The sub shells that follow up the filling pattern are 4d, 5p, 6s… So we can say that the elements which involve filling of 5s, 4d and 5p sub shell are accommodated in the fifth period .The total number of orbitals which these sub shell can have is nine and these orbitals  can accommodate 18  electrons. So there are 18 elements in the fifth period.

Q2. Give examples of three amphoteric oxides.

Solution

The examples of amphoteric oxides are Al₂O₃, ZnO, As₂O₃.

Q3. Differentiate between s and p block elements.

Solution

s block elements p block elements i) The general configuration of s-block elements is ns^1-2 i) The general electronic configuration of p block elements is ns²np^1-6 ii) They are soft metals. ii) Most of them are non-metals. iii) The compounds of s-block elements are predominantly ionic except lithium and beryllium which forms covalent compounds. iii) They form ionic as well as covalent compounds. iv) They show oxidation state of +1 and +2. iv) They show variable oxidation states.

Q4. The electronic configuration of an element is (n-1) d¹ ns² here n = 4. Find the position of the element in the periodic table?

Solution

The electronic configuration of the element is 3d¹4s². So, the element belongs to d-block, fourth period and group 3 of the periodic table.

Q5. Name the element which shows diagonal relationship with Beryllium (Be).

Solution

Aluminium shows diagonal relationship with Beryllium (Be).

Q6. Write the important uses of the Mendeleev's periodic table?

Solution

i) Classification of elements: In Mendeleev's periodic table the elements are classified into groups so it is easy to study the properties of elements. ii) Mandeleev left certain vacant spaces in his periodic table which provided a clue for the discovery of new elements. iii) With the help of Mendeleev's periodic table, doubtful atomic weights of certain elements can be determined.

Q7. What is the IUPAC name given to the elements present beyond fermium?

Solution

The elements beyond fermium (Z=100) are known as Trans fermium elements.

Q8. What are aerogens?

Solution

The elements of group 18, the last column of p-block are known as inert gasses or noble gases or aerogens.

Q9. Define valence. How does valence of an element vary along the period and group? Explain.

Solution

The combining capacity of an element is known as its valence. Variation of valence in a period – In a period, the number of valence electrons increases from 1 to 8 as we move across it. The valence to the elements with respect to hydrogen and chlorine increases from 1 to 4 and then decreases from 4 to 0.   Variation in a group – On moving down a group, the number of valence electrons remains same and, therefore, all the elements in a group exhibits same valence. For example, all the elements of group 1 have valence equal to 1 and those of group 2 have valence equal to 2.

Q10. From the given sets, choose the atom which has the largest ionisation enthalpy                 i)       F, O, N ii)      Mg, P, Ar iii)     B, Al, Ga

Solution

i) Among F, O and N, Fluorine has the highest ionisation enthalpy because it has smallest size and highest nuclear charge. In, general, ionisation enthalpy increases as we move from left to right in a period. ii) Among Mg, P and Ar, Ar has the highest ionisation enthalpy because Ar is a noble gas so it has stable electronic configuration and maximum nuclear charge. iii) Among B, Al and Ga, B has the largest ionisation enthalpy because on moving down a group, from top to bottom, the ionisation enthalpy decreases.

Q11. Halogens have the highest negative electron gain enthalpies in their respective periods. Explain.

Solution

Halogens have the highest negative electron gain enthalpies in their respective periods due to their small size and high effective nuclear charge.

Q12. What are magic numbers?

Solution

The physical and chemical properties of an element repeat themselves after the interval of 2, 8, 18 or 32 in their atomic number. So the numbers 2, 8, 18 and 32 are known as magic numbers.

Q13. Name two metals which have very low melting points?

Solution

Gallium and cesium have very low melting points.

Q14. Why noble gases have largest positive electron gain enthalpies in their respective periods? Explain.

Solution

The noble gases have a stable electronic configuration so they have largest positive electron gain enthalpies in their respective periods. 

Q15. Why do we call the d block elements as transition metals?

Solution

In the periodic table the left hand side of the d- block elements is occupied by the reactive metals of group 1 and 2 and towards the right hand side the less reactive elements of groups 13 and 14 are present. The d-block elements form a bridge or transition between the two so they are known as the transition metals.

Q16. The sixth period of the periodic table should have 32 elements. Explain this sentence on the basis of quantum numbers.

Solution

In the modern periodic table, each period starts with the filling of a new principal energy level. Thus, the sixth period begins with the filling of 6s orbital and continues till the filling of seventh energy level. According to the Aufbau rule the sub shell which follows 6s are 4f, 5d, 6p, and 7s. Therefore in the sixth period, electrons can be filled in only 6s, 4f, 5d and 6p sub shells. Now s sub shell has two, p sub shell has 3, d-sub shell has 5 and f-sub shell has 7 orbitals. Hence in all there are 16 orbitals that can be filled in this period which at the maximum can accommodate 32 electrons and therefore, sixth period has 32 elements.

Q17. Predict the formulae of the stable binary compounds that would be formed by the following pairs of elements i) Element 114 and fluorine ii) Element 120 and Oxygen

Solution

i) The element (M) with atomic number 114 belongs to group 14 of the periodic table so it will exhibit a valency of 2 (due to inert pair effect) and 4. The stable binary compound between this element and fluorine would have the formula MF₂. ii) The element (X) with atomic number 120 belongs to group2. Its valency would be 2. Thus, the formula of the compound between this element and Oxygen would have the formula XO.

Q18. Name the shortest and the longest periods of the periodic table?

Solution

The first period of the periodic table is the shortest period of the periodic table. The sixth period of the periodic table is the longest period of the periodic table. The seventh period is still incomplete.

Q19. Differentiate between Mendeleev's Periodic Law and Modern Periodic Law.

Solution

Mendeleev's periodic law Modern periodic law i) It states that the properties of elements are a periodic function of their atomic weights. i) It states that the properties of elements are periodic functions of their atomic numbers. ii) Mendeleev's periodic table is based on Mendeleev's periodic law. ii) Long form of periodic table is based on the modern periodic law.

Q20. The atomic number of an element A is 40. What are the group number, period and block of the element?

Solution

The electronic configuration of the element with atomic number 40 is: ⁴⁰X: 1s², 2s², 3s², 3p⁶, 4s², 3d¹⁰, 4p⁶, 5s², 4d² Since the last electron enters d sub shell, the element belongs to d- block. Since the outermost shell of the element is fifth, the element belongs to period 5 Group number of the elements of d-block is equal to sum of the electrons in outermost s-sub shell and d-sub shell of penultimate shell. Hence, group number of the element = 2 + 2 = 4. 

Q21. What is periodicity? Discuss its cause.

Solution

The periodical repetition of similar properties of the elements after certain regular intervals when the elements are arranged in order of increasing atomic number is called periodicity. This property is due to the recurrence of similar valence shell configuration after regular intervals.

Q22. Out of P, S, Cl and F which element has the most negative electron enthalpy. Also write the name of the element with least negative electron gain enthalpy.

Solution

Electron gain enthalpy generally becomes more negative across a period as we move from left to right. The order of negative electron gain enthalpy among P, S and Cl is Cl > S > P. The electron gain enthalpy becomes less negative as we move down the group. Adding an electron to the 2p orbital leads to greater repulsion than adding an electron to the larger 3p orbital. So, electron gain enthalpy of Cl is more negative than that of F. Hence the element with most negative electron gain enthalpy is Cl and the one with least negative electron gain enthalpy is P.

Q23. What is the relation between the number of elements present in each period and the number of atomic orbitals?

Solution

The number of elements in each period is twice the number of atomic orbitals available in the energy level.

Q24. i) Write the correct order of the chemical reactivity of F, Cl, O and N on the basis of their oxidizing power. ii) Explain the cause of diagonal relationship.

Solution

i) The oxidizing character increases across a period i.e. on moving from left to right. So, among F, O and N, oxidizing power decreases in the order F > O > N. However, with in a group, oxidizing power decreases from top to bottom. Thus, F is a stronger oxidizing agent than Cl. So, the overall decreasing order of oxidizing power is: F > Cl > O > N. ii) In the periodic table, along the period electro negativity increases and electropositivity increases along a group. As a result the two effects tend to cancel each other in moving diagonally from top left to bottom right. Therefore, the elements are diagonally related in this way tend to have similar properties.

Q25. Explain the nomenclature of an element according to the IUPAC system of nomenclature.

Solution

According to the IUPAC system the name of an element is derived directly from its atomic number by using the Latin words for their numbers. For example the word nil is used for 0,un for1, bi for2, tri for3, quad for 4,pent for 5, hex for 6, sept for 7, oct for 8 and enn for 9. The Latin words for various digits of the atomic number are written together in the order which makes the atomic number and ‘ium’ is added to the end. For example the IUPAC name of an element with atomic number 120 is 1 = un, 2 = bi and 0 = nil, so the IUPAC name of the element is un + bi + nil + ium = Unbinilium.

Q26. State modern periodic law:

Solution

The modern periodic law states that the physical and chemical properties of the element are periodic functions of their atomic number.

Q27. What is the relationship between the number of period and principal quantum number?

Solution

The main energy shell of the electrons is given by the principal quantum number. Each period in the periodic table begins with the filling of new energy shell. The number of period also states the principal quantum number.

Q28. Differentiate between lanthanide and actinide series.

Solution

Lanthanoid series Actinoid series i) The sixth period of the periodic table is known as the lanthanoid series. i) The seventh period of the periodic table is known as the actinoid series. ii) It involves the filling of 6s orbital. ii) It involves the filling of 7s orbital. iii) It contains 32 elements. iii) It is incomplete. iv) Due to the filling up of 4f orbitals it constitutes the first f transition series. iv) Due to the filling up of 5f orbitals it constitutes the second f transition series.

Q29. What were the main draw backs of the Mendeleev's periodic table?

Solution

The main draw backs of the Mendeleev's periodic table are as follows: i) The position of hydrogen in the periodic table was not certain, it was placed in first as well as eighth group. ii) Some elements of higher atomic weight were placed before the elements with lower atomic weight. iii) Lanthanides and actinides were not given a proper position. iv) Isotopes of elements were placed in the same position in the table. v) The noble gases were not given any space in the periodic table. vi) Some chemically similar elements were placed in different groups and some dissimilar elements were placed in the same group.

Q30. Differentiate between metals and non-metals. On the basis of atomic number and position in the periodic table arrange the following elements in increasing order of metallic character. Si, Be, Mg, P.

Solution

Metals Non-metal i) They have a strong tendency to lose electrons to form cations. i) They have a strong tendency to accept electrons to form anions. ii) They are highly electropositive. ii) They are highly electronegative. iii) They are good reducing agents. iii) They are good oxidizing agents. iv) Their oxides are of basic or amphoteric in nature. iv) Their oxides are acidic or neutral. Metallic character increases down a group and decreases along a period as we move from left to right so the increasing order of metallic character is: P < Si < Be < Mg < Na.

Q31. Write the general outer electronic configuration of s, p, d and f block elements. Also assign the position of elements having outer electronic configuration as i) ns² np⁴  for n=3 ii) (n-2) f⁷ (n-1) d¹ ns² for n=6, in the periodic table.

Solution

The general outer configuration of s block elements is ns^1-2 p block = ns² p^1-6 d block= (n-1) d^1-10ns^0-2 f block = (n-2) f^1-14 (n-1) d^0-1,ns²    i) ns² np⁴ for n=3 Ans) In this case the element belongs to third period of the periodic table as n=3. The group number of the element is 16 ii) (n-2)f⁷ (n-1) d¹ ns² for n=6 Ans)    In this case the element belongs to the sixth period of the periodic table. The group is lanthanoid. .

Q32. Among Na and Mg, which will have higher second ionisation enthalpy? Given that the atomic number of sodium (Na = 11) and magnesium (Mg = 12)

Solution

Among sodium and magnesium, sodium will have higher second ionisation enthalpy because in sodium the second electron has to be removed from second shell where as in the case of magnesium the second electron is removed from third shell.

Q33. Differentiate between electron gain enthalpy and electronegativity.

Solution

Electron gain enthalpy Electronegativity i) It is the property of an isolated atom of an element in gaseous state. i) It is the property of an atom of the element when it is bound to some other atom. ii) Its value can be determined experimentally. ii) The value of electronegativity can not be determined experimentally.

Q34. How can you predict the group, period and block of an element explain?

Solution

To know the group, period and block of an element first of all we write the electronic configuration of an element. The period is represented by the principal quantum number of the valence shell. Block is predicted on the basis of sub shell which receives the last electron. Group is predicted on the basis of the number of electrons in the penultimate or the outer most shell.

Q35. Find out the IUPAC name and symbol of an element .Given that the atomic number of the element (Z = 108)?

Solution

The roots for the numbers 1, 0 and 8 are Un, Nil and Oct respectively. So IUPAC name and symbol for the element are unnilotium and Uno respectively.

Q36. What are metalloids?

Solution

The elements which exhibit the properties of metals as well as non-metals are known as metalloids. For example silicon, germanium, arsenic, antimony and tellurium etc.

Q37. Why do halogens act as good oxidizing agents?

Solution

The halogens can gain electrons easily to form corresponding ions so they act as oxidizing agents.

Q38. An element A has atomic number (Z = 14) where would you locate it in the periodic table in terms of periods and group?

Solution

The atomic number of the element is 14 so its electronic configuration is 1s², 2s², 2p⁶, 3s², 3p². Since the last electron enters in 3p orbital so it belongs to third period and group number 14 of the periodic table.

Q39. In which period of the periodic table are the man made radioactive elements present? Why are the 4f and 5f transition series placed separately in the periodic table?

Solution

The man made radioactive elements are present in sixth period of the periodic table. The 4f and 5f transition series of elements are placed separately in the periodic table to maintain its structure and to preserve the principle of classification.

Q40. Among the following groups, select the species which has the smallest radius. Also give appropriate reasons to support your answer. i)      O, O^-, O^{2- ii)      K+, Sr2+, Ar iii)     Si, P, Cl}

Solution

i) Among O, O^-, O^2- the species O has the smallest radii because the radius of the anion is always larger than the radius of the atom from which it is formed. O^-and O^2- are anions of oxygen. ii) In K⁺ and Ar the outer most shell is third where as in Sr²⁺ it is fourth. Out of K⁺, Sr²⁺ and Ar, K⁺ has smaller size because it has greater nuclear charge. iii) Among Si, P and Cl, Cl has the smallest radius. Si, P and Cl belong to the same period. In a period the atomic radius decreases with increase in atomic number due to increase in the effective nuclear charge.