Question 1

Question 2Consider the section of the periodic table given below:Groupnumbers1A1IIA2IIIA13IVA14VA15VIA16VIIA17O18 Li D  OJNe AMgESi HK  BC FG  LSome elements are given in the above table in their own symbol and position in the periodic table, while others [shaded] are shown with a letter. With reference to the table:(i) Which is the most electronegative?(ii) How many valence electrons are present in G?(iii) Write the formula of the compound between B and H.(iv) In the compound between F and J, what type of bond will be formed?(v) Draw the electron dot structure for the compound formed between C and K.

Accepted Answer

(i) J is the most electronegative.(ii) G has 5 valence electrons.(iii) B2H is the name of the compound between B and H.(iv) Covalent bond will be formed between F and J.(v) Electron dot structure for the compound formed between C and K is shown below:

Question 2

Question 1Choose the correct answer :(i) Ionization potential increases over a period from left to right because the:Atomic radius and nuclear charge increasesAtomic radius and nuclear charge decreasesAtomic radius increases and nuclear charge decreasesAtomic radius decreases and nuclear charge increases(ii) An element A belonging to Period 3 and Group II will have :3 shells and 2 valence electrons2 shells and 3 valence electrons3 shells and 3 valence electrons2 shells and 2 valence electrons

Accepted Answer

(i) Atomic radius decreases and nuclear charge increasesReason — The ionization potential of element tends to increase across a period from left to right because the atomic size decreases due to an increase in nuclear charge and electrons in the outermost shell are more strongly held because of which greater energy is required to remove the electron.(ii) 3 shells and 2 valence electronsReason — Period of an element determines the number of shells and group determines number of valence electrons.

Question 3

Question 4Name the elements in correct order of their increasing atomic numbers present in the first, second and third short periods of the periodic table. State each elements electronic configuration.

Accepted Answer

Elements of first, second and third period in increasing order of their atomic number are mentioned below (atomic number of each element is mentioned in brackets):First period — H(1), He (2)Second period — Li (3), Be (4), B (5), C (6), N (7), O (8), F (9), Ne (10)Third period — Na (11), Mg (12), Al (13), Si (14), P (15), S (16), Cl (17), Ar (18)Electronic configuration of the above mentioned elements is as follows —H — 1He — 2Li — 2, 1Be — 2, 2B — 2, 3C — 2, 4N — 2, 5O — 2, 6F — 2, 7Ne — 2, 8Na — 2, 8, 1Mg — 2, 8, 2Al — 2, 8, 3Si — 2, 8, 4P — 2. 8, 5S — 2, 8, 6Cl — 2, 8, 7Ar — 2, 8, 8

Question 4

Question 5Give a reason why :(a) completion of each period is logical.(b) period-2 elements are called 'bridge elements'.

Accepted Answer

(a) Completion of each period is logical, since each period begins with an element having one electron in the outer most shell and ends with zero group element having completely filled outer shell.(b) The elements of the second period show resemblance in properties with the elements of the next group of third period, due to very less electronegativity difference. This leads to a diagonal relationship, viz. Li and Mg, Be and Al, B and Si. These elements are hence called Bridge elements.

Question 5

Question 6State the property trends in general on moving from left to right in a period of the periodic table.

Accepted Answer

The property trends in general on moving from left to right in a period of the periodic table are :Number of valence electrons — increases by oneAtomic radius — decreases.Ionization potential — increases.Electron affinity — increases (exception, electron affinity is zero for noble gases).Non-metallic character — increases.Metallic character — decreasesElectronegativity — increases (with the exception of noble gases, they have complete octet so do not attract electrons to itself).

Question 6

Question 7State :(i) the bonding and state of chlorides of period-3 — group 1 [IA], 15[VA], 16 [VIA] and(ii) the bonding and character of oxides of period-3 — group 1 [IA], 13[IIIA] and 16[VIA].

Accepted Answer

(i) The element of group 1 [IA] of period 3 is Na and it's chloride forms ionic bond and is in solid state.The element of group 15 [VA] of period 3 is P and it's chloride forms covalent bond and is in liquid / solid state.The element of group 16 [VIA] of period 3 is S and it's chloride forms covalent bond and is in liquid state.(ii) The element of group 1 [IA] of period 3 is Na and it's oxide forms electrovalent bond and is strongly basic in character.The element of group 13 [IIIA] of period 3 is Al and it's oxide forms electrovalent bond and is amphoteric in character.The element of group 16 [VIA] of period 3 is S and it's oxide forms covalent bond and is acidic in character.

Question 7

Question 9State the type of elements present in :(a) group 1[IA](b) group 2 [IIA](c) group 3 to 12 [IB to VIIB and VIII](d) group 13 to 16 [IIIA to VIA](e) group 17 [VIIA](f) group 18 [0].

Accepted Answer

(a) Group-1 [IA] — Alkali metals(b) Group-2 [IIA] — Alkaline earth metals(c) Group-3 to 12 IB to VII B, VIII — Transition elements - inner transitional elements.(d) Group 13-16 [III B to VI A] — Post Transition elements.(e) Group 17 (VII A) — Halogens.(f) Group 18 (0) — Noble / Inert gases.

Question 8

Question 10What are transition elements and inner transition elements. State the position of the inner transition elements. State why noble gases are considered unreactive elements.

Accepted Answer

Transition Elements — Elements belonging to Groups 3 to 12 are called transition elements. The valence electron of these elements is in d orbital. They are metals and lie between strongly electropositive metals on the left and least electropositive elements on the right. They all have similar properties.Inner Transition Elements — Elements belonging to Group 3 in 6th and 7th period are called Inner transitional elements. The valence electron of these elements is in f orbital. They consists of two horizontal rows of elements which are placed at the bottom of the table. These rows are called Lanthanides (rare earth) and Actinides (radio active). Each row has 14 elements.Noble gases are unreactive because their octet is complete and they have a stable electronic configuration.

Question 9

Question 11State the characteristics which remain similar and those which show a transition on moving down a sub-group.

Accepted Answer

Characteristics which remain similar on moving down a sub-group are as follows:Valency of electrons.Chemical properties.Characteristics which show a transition on moving down a sub-group are as follows:Metallic character increases down the sub-group.Number of electron shells increases by one as we move down each sub-group.

Question 10

Question 12Compare the properties of the elements of group 1[IA] i.e. alkali metals and group 17 [VIIA] i.e., halogens.

Accepted Answer

Below table shows the comparison of the elements of group 1[IA] i.e. alkali metals and group 17 [VIIA] i.e., halogens:PropertyGroup 1[IA]Group 17 [VIIA]ElementsLi, Na, K, Rb, Cs, FrF, Cl, Br, I, AtValencyUnivalent (1 valence electron)Univalent (7 valence electrons)NatureHighly reactive, highly electropositive, light soft metalsHighly reactive, highly electronegative, non - metalsConductivityGood conductors of heat and electricityBad or non conductors of heat and electricityReducing / Oxidizing natureStrong reducing agentsStrong oxidizing agentsElectronegativityLow electronegativityHigh electronegativity

Question 11

Question 13Explain the term:(a) periodicity in properties of elements(b) periodic properties(c) periodicity of elements

Accepted Answer

(a) Periodicity in properties of elements — The phenomenon of occurrence of characteristic properties of elements at definite intervals in the modern periodic table when elements are arranged in increasing order of their atomic numbers is called Periodicity in properties of elements.(b) Periodic properties — The properties which appear at regular intervals in the periodic table are called periodic properties. Periodic Properties are:Atomic radiiIonization potentialElectron affinityElectronegativityNon-Metallic and Metallic character.DensityMelting and boiling points.Nature of oxides, oxy-acids, hydrides.(c) Periodicity of elements — Gradual change in properties of elements when they are arranged in increasing order of atomic number in the periodic table is called the periodicity of elements.

Question 12

Question 14State the reasons for periodicity of elements in periods and groups.

Accepted Answer

Reasons for Periodicity in properties in periods and groups is as follows —After definite intervals of atomic number, similar valence shell electronic configuration occurs i.e., same number of electrons are present in the outermost orbit of the elements.Properties of elements depend upon the number and arrangement of electrons in various shells including valence shells.In the same period or sub-group, increase or decrease in a particular property is due to gradual change in electronic configuration in the arranged elements.

Question 13

Question 17Explain the trend in atomic radii on moving down a group, with reference to the alkali metals in Group 1 [IA].

Accepted Answer

Atomic radii of an atom increases on moving down a group. As we move down a group, the number of shells increases and the nuclear charge also increases. But increase in the number of shells dominates over increase in nuclear charge therefore, overall atomic size increases.For alkali metals in Group 1 [IA], Li which is at the top of the group has the smallest atomic radius whereas Cs at the bottom of the group has the largest atomic radius. The atomic radii of the elements has the following relation:Li < Na < K < Rb < Cs

Question 14

Question 19Explain the trend in general of ionization potential of elements :(a) on moving from left to right across a period(b) on moving down a group.Give reasons for the change in the periodic trend in each case.

Accepted Answer

(a) On moving from left to right across a period, the ionization potential increases.The ionization potential of element tends to increase across a period because the atomic size decreases due to an increase in nuclear charge and electrons in the outermost shell are more strongly held because of which greater energy is required to remove the electron.(b) On moving down a group ionization potential decreases.On moving down the group, atomic size, as well as, nuclear charge increases. Due to the increase in atomic size the ionization potential decreases and due to the increase in nuclear charge the ionization potential should increase However, the effect of increase in atomic size dominates over the effect of increase in nuclear charge. Hence, ionization potential decreases down the group.

Question 15

Question 22With reference to the alkali metals in Group 1 [IA] and the halogens in 17 [VIIA] explain the trend in ionization potential, electron affinity and electronegativity on moving down the groups in the periodic table.

Accepted Answer

Below table explains the trends in ionization potential, electron affinity and electronegativity on moving down the groups in the periodic table: Alkali MetalsGroup 1 [IA]HalogensGroup 17 [VIIA]IonizationPotentialOn moving down the group both atomic size and nuclear charge increases but atomic size increase dominates over nuclear charge increase hence Ionization Potential decreases down the group.∴ Li > Na > K > Rb > CsSimilarly for Halogens too Ionization Potential decreases down the group.∴ F > Cl > Br > IElectron AffinityOn moving down the group, electron affinity decreases as atomic size increase dominates over nuclear charge increase hence the atom attracts the electrons with a lesser force.∴ Li > Na > K > Rb > CsHere also electron affinity decreases in general on moving down the group but Fluorine is an exception here as it has lesser electron affinity than Chlorine due to its electronic configuration.∴ F < Cl > Br > IElectronegativitySimilar to electron affinity, electronegativity decreases on moving down the group.∴ Li > Na > K > Rb > CsElectronegativity decreases on moving down the group.∴ F > Cl > Br > I

Question 16

Question 24Explain the trends from metallic to non-metallic character of the different elements in the first three periods.

Accepted Answer

On moving across a period, nuclear pull increases due to increase in atomic number and thus the atomic size decreases. Hence, the elements cannot lose electrons easily. Therefore, metallic nature decreases across a period moving from left to right and non-metallic character increases.The alkali metals ( group 1 [IA]) and alkaline earth metals (group 2 [IIA]), placed on the left side of the table are most metallic in nature and the halogens (group 16 [VIA]) placed on the right side of the table are most non-metallic in nature.

Question 17

Question 25Explain with reasons the trends in metallic and non-metallic character down a group.

Accepted Answer

Metallic/Non-Metallic character depends on atomic size and nuclear charge. Increase in atomic size increases the Metallic nature and increase in nuclear charge decreases the metallic nature. On moving down the group both atomic size and nuclear charge increases. But the atomic size increase dominates over nuclear charge increase. Hence, tendency to lose electrons increases. Thus, metallic character increases as one moves down a group and non-metallic character decreases.

Question 18

Question 26State how density and melting points of elements varies across a period and down a group.

Accepted Answer

(i) Density — Density of elements across a period increases gradually to maximum and then it decreases slightly. Down a group density of elements increases gradually.(ii) Melting point — Across a period from left to right, melting point increase upto group 14(IV A) and then decreases. The melting point of metals decrease down the group. The melting point of non-metals increase going down a group

Question 19

Question 27State the general trend in periodicity in properties of oxides, hydroxides, oxy-acids and hydrides of compounds of elements across a period and down a group.

Accepted Answer

Below table shows the general trend in periodicity in properties of oxides, hydroxides, oxy-acids and hydrides of compounds of elements across a period and down a group: Across a periodDown a groupOxidesVaries from strongly basic to strongly acidicVaries from acidic to basicHydroxidesVaries from strongly basic to amphotericVaries from less basic to strongly basicOxy-acidsVaries from weak oxy-acids to strong oxy-acidsVaries from strong oxy-acids to weak oxy-acidsHydridesVaries from strongly basic to strongly acidicVaries from less acidic to more acidic

Question 20

Question 28State the relation between atomic number and atomic mass for light elements. State which elements are considered radioactive giving reasons.

Accepted Answer

Electronic configuration of lighter elements shows that the elements which have an even number of proton, for example, atomic numbers like 24He_2^4	ext{He}24​He, 612C_6^{12}	ext{C}612​C etc., have their mass numbers twice the atomic numbers except for 49Be_4^9	ext{Be}49​Be and 1840Ar_{18}^{40}	ext{Ar}1840​Ar.Elements which have an odd number of protons like 37Li_3^7	ext{Li}37​Li, 511B_5^{11}	ext{B}511​B etc., have their mass number twice the atomic numbers + 1 (A = 2Z + 1) except 714N_7^{14}	ext{N}714​N and 11H_1^1	ext{H}11​HElements with neutron:proton ratio 1.5 and above are considered as radioactive as the nucleus of such elements becomes unstable causing their radioactive decay. For example, in Uranium (92235U)(_{92}^{235}	ext{U})(92235​U):No. of protons (p) = 92No. of neutrons (n) = 235 - 92 = 143n : p = 14392\dfrac{143}{92}92143​ = 1.5543A neutron:proton ratio greater than 1.5 makes Uranium radioactive.

Periodic Table — Periodic Properties & Variation of Properties

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2014

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Unit Test Paper I — Periodic Table