Explore topic-wise InterviewSolutions in Current Affairs.

The maximum chemical reactivity at the extreme left (among alkali metals) is exhibited due to the loss of an electron leading to the formation of a cation due to low ionization enthalpy and at the extreme right (among halogens) shown by the gain of an electron forming an anion.

Conc. H₂SO₄ removes the moisture from gases and it can also remove water molecules from blue vitriol. So conc.H₂SO₄ is used as dehydrating as well as drying agent.

(a) 2.

For groups 1 and 2, the number of valence electrons is equal to the group number.

(b) 2 .

Valency is determined by the number of valence electrons present in the atom of the element.

(c) 5 .

For groups 13 to 18, the number of valence electrons is equal to (group no. – 10).

(d) 3 .

The number of electrons lost or gained by one atom of an element to achieve the nearest inert gas configuration, gives us the valency.

(a) Sodium hydrogen sulphate is not an acid but undergoes partial replacement of the ionisable hydrogen atom and behaves as an acidic salt to give H⁺ ions.

(b) As calcium chloride absorbs moisture and keeps the compound dry, so it is used in desiccators as a drying agent.

(a) The main characteristic of last elements in a period is that they all have 8 valence electrons in their atoms except helium. Such elements are called noble elements.

(b) (i) 2

(ii) 8.

The first elements in the periods of the periodic table have 1 valence electron. Such elements are called alkali metals.

(c) Cl > F > Br > I

(d) Ca < Al < C < O < F

1. O or F. Both O and F lie in 2e” period. As we move from O to F the atomic size decreases. Due to smaller size off nuclear charge increases. Further, gain of one electron by 

F → F^- 

F^- ion has inert gas configuration, While the gain of one electron by 

O → O^- 

gives O ion which does not have stable inert gas configuration. Consequently, the energy released is much higher in going from

F → F^- 

than going from O → O^- . In other words electron gain enthalpy off is much more negative than that of oxygen.-

2. The negative electron gain enthalpy of Cl (e.g. ∆H = – 349 mol^-1) is more than that of F (e.g. ∆H = -328 U mol^-1 ). 

The reason for the deviation is due to the smaller size off. Due to its small size, the electron repulsion in the relatively compact 2p-subshell are comparatively large and hence the attraction for incoming electron is less as in the case of Cl.

On going down in a group of the periodic table, the metallic character of elements increases.

On moving from left to right in a period, the atomic size decreases.

On going:

(i) From left to right across a period, atomic radius decreases as one proton and one electron are added continuously, therefore effective nuclear charge increases.

(ii) down a group in the periodic table, atomic radius increases because the number of shells goes on increasing, therefore, the distance between nucleus and valence shell increases

(i) Since each element contains the same number of valence electrons, n in the outermost shells of their atoms, therefore X, Y and Z, belong to the same group.

(ii) The atomic radii increase from X to Z so metallic character increases from X towards Z.  

(iii) X, Y and Z have melting points above 25^oC (room temperature). Therefore, X, Y and Z are solid at room temperature.

(iv) The ionization potential decreases from X to Z because they belong to the same group in the descending order.

It is a number assigned to express the acidity or alkalinity of a solution which varies from 1 to 14. The pH number less than 7 indicates acidity, while pH number more than 7 indicates alkalinity. The pH of pure water is 7 and it is neutral.

1. Size of the atom: 

The new electron which was added experiences stronger attraction to its nucleus if the atoms are smaller in size. 

Atomic size α \(\frac{1}{Electron\,gain\,enthalpy}\)

2. Nuclear charge: 

The new electron which was added experiences stronger attraction to its nucleus if the atom possess greater nuclear charge. Nuclear charge α Electron gain enthalpy 

3. Electronic configuration: 

An atom with stable electronic configuration has no tendency to gain an electron. Such atoms have zero or almost zero electron gain enthalpy.

(i) Nitrogen: K shell-2       L shell-5

Phosphorus: K shell-2      L shell - 8       M    shell-5

(ii) Phosphorus will be less electronegative because its elections are further away from the nucleus and thus nucleus can be easily lost.

The electron gain enthalpy of an element is the amount of energy released when an electron is added to the neutral gaseous atom. 

A + electron → A^- + energy (E.A) 

Unit of electron affinity is KJ mole^-1 .

1 pm =10^-12m.

Atomic radius: 37 x 10^-12m

To measure the degree of acidity or alkalinity .

(a) F < N < Be < Li 

(b) Cl < Br < I < At

The pH of pure water is equal to 7.

The name of the metals is

• Magnesium
• Sodium
• Chlorine
• Lithium

The atomic size increases on moving down the group. This is because of the increase in a number of shells due to which the distance between the outermost electron and the nucleus increases. 

The atomic size decreases on moving along a period. This is because of the increase in the effective nuclear charge on moving from left to right which tends to pull the electrons towards the nucleus.

Elements present in the same group have a same number of electrons in their valence shells. On moving down a group, the number of shells increases but the number of electrons in the valence shell remains the same. That’s why the elements of the same group have similar properties.

Lithium is an alkali metal in the second period.

Two elements of group 1 are Sodium (Na) and potassium (K).
Their electronic configurations: Na = 2,8,1; K : 2,8,8,1
Similarity: Both have one valence electron.
Formula of their oxides: Na₂O; K₂O.

Answer is Lithium.

pH of pure water is 7 at 25^oC. No, the pH does not change when common salt is added

Fluorine is the halogen in the second period.

Answer is Magnesium.

Right side of the period are the nonmetals.

The answer is (b) Na >Mg >Al >Si > Cl

• Na has 1, magnesium has 2 , aluminium has 3 and Chlorine has 7 electrons in its valence shells. 
• Hence Sodium shows maximum metallic characters followed by Magnessium, aluminium and chlorine shows non-metallic properties.

The answer is (c) E₂O₃

The answer is (b) Li < Be < C < O < F 

• Li is on the left of in the 2^nd period of modern periodic table followed by berrylium. 
• Fluorine is at right next to Neon. 
• Hence Fluorine shows maximum non-metallic characters followed by Oxygen, Berrylium, carbon and Lithium.

₁₁Na has the highest metallic character.

Eka-aluminium has the properties similar to the aluminium so it forms the same type of oxide as that of aluminium i.e. E₂O₃.

Answer is Chlorine.

The tendency of an element to form anion or electronegativity is the nonmetallic character of element.

Answer is Fluorine.

Some salts, while crystallizing out form their solutions, unite with definite quality of water which is known as water of crystallization.

Four substances which contain water of crystallization:

Na₂CO₃. 10H₂O Washing soda

MgSO₄. 7H₂O Epsom salt

K₂SO_4.Al2(SO₄)_{3 .} 24H₂O Potash alum

Na₂SO₄. 10H₂O Glauber's salt

(a) Na or K  

(b) Ca 

(c) Hg 

Hg < Ca < Na < K

Since, we know that elements in 16^th group have 6 electrons in their outer most shell i.e. the valence electrons are 6. Therefore, we can say that B has 6 valence electrons. 

(Note: For this case ignore the period.) 

(i) We know that element in lower period have smaller radius as compared other as they have less no. of shells. Also, going along period the size of atom decreases as the effective nuclear charge on outer electrons increases. So, B will have smallest size as it lies in 1st period and 16th group. 

(ii) We know that, the metallic character increases going down the group and decreases going right along the period. Thus C will be most metallic of all. 

(iii) Since C and A lie in 1^st and 2^nd group so these can readily lose electron and thus can form basic oxides. 

(iv) We know that elements of 15^th group need only three electrons to complete their octet configuration and thus show valency 3. So, D will show valency 3. 

(v) We know that tendency to gain electron or electron gain enthalpy increases going right along period and decreases going down the group. Thus, B will show highest tendency to gain electrons

(i) The element X has atomic number=20, it means that the element is Ca. It has electronic configuration as: 2,8,8,2. The number of valence electrons is 2 which it can lose easily. Thus element X (Ca) is a metal. 

(ii) Mg has atomic number 12 and electronic configuration as: 2, 8, 2. Also, it has a lesser number of shell and thus its valence electrons lie closer to nucleus as compared to X(Ca) which has its valence electrons in 4^th shell, so Mg is less reactive than X(Ca). Thus X(Ca) is more reactive than Mg. 

(iii) Since X contains 2 electrons in last shell and it can readily lose them so its valency is 2.

F has maximum non-metallic character.

(i) As we can see it is given that X is surrounded by all other elements given above and there are numbers given 34 and 36. So, X must have atomic number 35. And this can be verified with periodic table where atomic number 35 corresponds to Bromine. 

(ii) As atomic no. 36 corresponds to Neon (Ne) having noble gas configuration: 2, 8, 18, 8 which means 18^th group element so X (Br) with atomic no. 35 will lie in group just before this that is 17^th group. Also, X (Br) has electronic configuration: 2, 8, 18, 7 which means it has 4 shells or n=4 and lies in 4^th period. So X (Br) lies in 4^th period and 17^th group. 

(iii) Electric configuration of elements with given atomic numbers, 

Z=17: 2, 8, 7 

Z=34: 2, 8, 18, 6 

Z=36: 2, 8, 18, 8 

Z=53: 2, 8, 18, 18, 7 

It can be easily seen that elements with atomic number 34 and 36 lie in same period as have same number of shells n=4 and all other elements are from different periods.

(a) A is a non-metal because it can gain electrons easily, it has 7 valence electrons and form negative ions to become stable. 

(b) The atomic number of B is less than C, it has less nuclear charge, less force of attraction between protons in the nucleus and valence electrons, hence its size is bigger than C. 

(c) Element ‘C’ has 7 valence electrons, it can gain 1 electron to become stable so its valency is 1.

i. True.

ii. False. (Elements are classified on the basis of their electronic configuration.)

iii. True.

iv. False. (Lanthanides and actinides are also called the f-block elements.)

v. True.

vi. False. (In a period, atomic size decreases from left to right.)

vii. False. (In a period. the metallic character decreases from left to right.)

viii. False. (In a group, the metallic character increases from top to bottom.)

ix. True.

i. Octaves

ii. Atomic number

iii. Group 17

iv. Liquid

v. 2, 7

vi. Vertical columns

(i) As the effective nuclear charge acting on the valence shell increases across the period, the tendency to lose electrons decreases due to this metallic character decreases.

(ii) Atomic size increases in a group because new shells are being added as we go down the group. This increases the distance between the outermost shell and nucleus.

(iii) The reactivity of element depend upon their tendency to lose or gain electrons to complete their outermost shell, greater is the tendency to lose/gain electron greater is the reactivity

So, in a period first tendency to lose electron decreases so reactivity decreases and the tendency to gain electron increases so the reactivity increases.

When the elements are arranged in an increasing order of their atomic masses, the properties of the eighth element are similar to those of the first. It is found that Na is the eighth element from Li and both of them have similar properties.