Explore topic-wise InterviewSolutions in Current Affairs.

(a) 3rd period.

(b) Ionic compound .

(c) A and B.

(d) H.

(e) CG₃.

(b) Isotopes

To make the study of these elements easy, these elements have been divided into few groups in such was that elements ire the same group have similar properties

The element belongs to period 4.

The elements lithium, sodium and potassium form a Dobereiner’s triad. Lithium is the first element of this triad, sodium is the middle element whereas potassium is the third element of the triad. Sodium (middle element) has atomic mass 23. According to Dobereiner,

Atomic mass of Sodium = At. mass of Li + At. mass of K/2 = 7 + 39/2 = 23

(i) Non-metal .

(ii) 6 .

(iii) 2 .

(iv) Oxygen .

(v) Na 2 Y .

Endothermic reaction: The reaction in which heat is absorbed is called an endothermic reaction.

when KNO_3(s) dissolves in water, there is absorption of heat during the reaction and the temperature of the solution falls.

KNO_2(s) + H₂O_(l) + Heat → KNO_3(aq)

A) Both (A), (R) are correct, Assertion supports Reason.

At room temperature, the decomposition of hydrogen peroxide into water and oxygen takes place slowly. However, the same reaction occurs at a faster rate on adding manganese dioxide (MnO₂), powder in it.

A) combination

Correct option is B) Ca(OH)₂ 

(i) Electronic Configuration -2,8,2

Valency - 2.

(ii) Metal

There are two electrons in its outermost shell and it easily loses them to form a positive ion.

(iii) M -2

O-2

M₂O₂ = MO

It is a basic oxide.

EGckonic Configuration of 'P'-2,8,7

Group number - 17

Period number  3rd Period

Electronic Configuration of 'Q' - 2,8,8,1

Group number - 1

Period number - 4^th Period

(a) Configuration of X (19) = 2,8,8.1.
(b) It belongs to fourth period and its valency is 1.
(c) Basic oxide (X₂O)
(d) X₂O + H₂O  ------>  2XOH

Atomic number of X = 2 + 8 + 2 = 12

Atomic number of Y = 2 + 8 + 6 = 16

For group II elements, the group no. (2) is equal to the valency of the elements present in this group. So two such elements belonging to group II are Calcium and Magnesium.

(i) It is a metal.

Since it has two electrons in its outermost shell/two valence electrons, which it can lose easily.

(ii) K(19) is placed before Ca(20) in the same period/fourth period.

Since the atomic radius decreases along a period, the atomic radius of calcium is smaller than that of potassium.

(iii) The formula of oxide of calcium is CaO, because of the valency of calcium as well as that of oxygen is 2.

Lithium is present in the 1^st group and the 2^nd period. On moving along the period from left to right, the atomic number increases. The atomic number of Li is 3 so the atomic number of next element will be 4. Thus the next element to Li is Beryllium.

‘X’ has 1 valence electron and it belongs to a 4^th period so it is Potassium (K) and the ‘Y’ is of the 3rd period and it has 7 electrons in an outermost cell with atomic number 17 so it is Chlorine (Cl). We know that poopt5assium is a metal.

Hydrogen has one shell and one valence electron.

Fluorine is a most reactive element in group 17 because of its small size and high electronegativity by which it accepts electron easily and forms a bond with another element.

The electronic configurations of elements help us to explain the periodic recurrence of physical and chemical properties. Anything which repeats itself after a regular interval is called periodic and this behaviour is called periodicity

(i) Mg. 

(ii) Al. 

(iii) O and S. 

(iv) Most reactive non-metal of group 17 is fluorine because its electronegativity is more. Its symbol is F.

The most reactive metals belong to group IA.

• Elements of 1^st group are called alkali metals. Their electronic configuration is ns¹. 
• Elements of 2^nd group are called alkaline earth metals. Their electronic configuration is ns² .

(i) Two elements that can show a valency of two with respect to oxygen are calcium and barium. 

(ii) Two elements that can form oxides of type XO₃ are chromium (Cr) and sulphur (S). Formulae of their oxides are: CrO₃ and SO₃. 

(iii) The innermost shell is k shell, followed by L shell and then comes the M shell. We can write an electronic configuration which can satisfy the given condition as: 2,8,4. We can see that the number of electrons present in L shell is double of the electrons resent in M shell. This is possible for an element with atomic no.=14. Thus the element is Si.

The similarity is observed in valence electrons of these elements. The valence electron in these elements is one.

First group elements are also known as alkali metals. They possess the following properties :

(i) These elements exhibit +1 valency.

(ii) These are very reactive as they are not found freely in nature.

The two elements X and Y will show same chemical properties because they have same number of valence electrons in group. They form positively charged ions by losing one electron

• s-block elements : ns^1-2 where n = 2 – 7. 
• p-block elements : ns² np^1-6 where n = 2 – 6. 
• d-block elements : (n – 1) d^1-0 ns^0-2 where n = 4 – 7. 
• f-block elements : (n – 2) f^0-14 (n – 1) d^0-1 ns² where n = 6 – 7.

The metallic character of a metal increases with increase in the size of its atom.

(i) The electronic configuration of Q is :2,8,3. It has three valence electrons, so it has a valency of three. 

(ii) We can classify an element as a metal or non-metal by looking at its position in periodic table. Those lying on left side of periodic table are metals and those lying on right side are non-metals. 

(iii) The element P is most metallic because it can easily loose two electrons and lies on the left side of the periodic table. Metal oxides are basic in nature, therefore oxide of P will be most basic

X and Y will show similar chemical properties as these have same valence electrons.

x=2,(1)

Y = 2,8, (1)

(a) (i) Elements of 18 groups are noble gases. So Neon (Ne) with atomic number 10 and Argon (Ar) with atomic number 18 are the noble gases because these have complete octet.

(ii) Elements of 17 group are halogens. So Fluorine (F) with atomic number 9 and Chlorine (Cl) with atomic number 17 are halogens. 

(iii) Elements of 1 group are alkali metals except hydrogen (H). So Lithium (Li) with atomic number 3 and Sodium (Na) with atomic number 11 are alkali metals. 

(iv) Elements with valency 4 are elements of group 14. So Carbon (C) with atomic number 6 and Silicon (Si) with atomic number 14 are elements with valency 4. 

(b) Element with atomic number 3 is Li which has 1 valence electron and element with atomic number 17 is Cl has 7 valence electrons. Element with atomic number 17 wants one electron to complete its octet. So the formula will be LiCl. 

(c) The electronic configuration of element with atomic number 10 is 

10^Ne- 2, 8

(a) (i) All the elements of a group have similar chemical properties because they have same no. of valence electrons in their outermost shell.

(ii) All the elements of a period have different chemical properties because they have different no. of valence electrons in their atoms.

(b) Order of atomic numbers of elements: X < Z < Y. Because as the atomic number increases in a period from left to right, the size of atoms goes on decreasing

(a) On moving from left to right in a period of the periodic table, the atomic size decreases. As we move from left to right in a period, the atomic number of elements increases which means that the no. of protons and electrons in the atoms increases. Due to large positive charge on the nucleus, the electrons are pulled in more close to the nucleus and the size of atom decreases.

(b) On moving from left to right in a period, the metallic character of elements decreases.

(a) X₍₂₀₎-2,8,8,2

Valence electrons- 2

Hence valency is   2

(b) It is a metal

(c) XCl₂  

(d) It is more reactive than Mg as reactivity increases down the group Mg- III Period And X₂₀ (Ca)- IV Period

(a) Ionic compound.

(b) Yes .

(c) XY₂ .

(d) 2 .

(e) 7 .

K is more reactive than Li because the size of K is bigger than Li and due to this bigger size, the effective nuclear charge decreases so the attraction of nucleus on valence electrons also decreases. So K loses its valence electrons more easily than Li.

In a group atomic size: Increases down the group.

ln a period atomic size: decreases in moving from left to right.

It will be 7 in X as well as in Z

The reason being that number of electrons in the outermost shell in the elements in same group is same.

Electronic configuration of element 'y' with atomic number 3=2, 1 

Element 'A' with atomic number 17 = 2,8,7

The formula of the compound: YA.

Noble Gases

Noble gases are also known as inert gases and do not take part in chemical reactions. They have their outermost shell complete and thus remain stable. They do not generally combine with other substances, nor are they affected by oxidising agents or by reducing agents. They are placed in the 18 or VIIIA group. Since, the outermost shell is complete, the valency is zero, hence VIIIA group is also referred to as zero group.

This reaction shows double displacement. Here, silver displaces potassium to form silver chloride. On the other hand, potassium displaces silver to form potassium nitrate.

Liebig’s method.

Position of actinoids in the periodic table: 

i. Actinoids belongs to the third group of periodic table in the seventh period. 

ii. In the periodic table, as we move from one element to another, either from left to right or from top to bottom, the properties exhibit a gradual change. But these fifteen elements are so similar to one another, that they cannot be placed one after the other or one below the other. 

iii. As the fourteen elements i.e. Th(90) to Lr(103) are closely similar to Ac(89), the best place for them is alongwith actinium(89) i.e., third group (3^rd column) and seventh period in the periodic table. 

iv. In case these elements are give different positions in order of their increasing atomic numbers, the symmetry of the periodic table would be disrupted. Due to this reason, the actinoids are placed at the bottom of the periodic table with a reference to the third group in the seventh period i.e., the position of actinium.

Electronic configuration of actinium and 5f-series of f-block elements:

i. The 5f-series includes elements from thorium (Th) to lawrencium (Lr).

The electronic configuration of these elements can be expressed in terms of Rn (Z = 86).

ii. Electronic configuration of Rn (Z = 86) = 1s² 2s² 2p⁶ 3s² 3p⁶ 3d¹⁰4s² 4p⁶ 4d¹⁰5s² 5p⁶ 5d¹⁰5f¹⁴6s² 6p⁶ .

Therefore, General electronic configuration of actinoids : [Rn] 5f^1-14 6d^0-1 7s²

iii. The electronic configuration of actinium (Z = 89) is [Rn] 5f⁰ 6d¹ 7s² . It does not contain any 5f electron.

iv. Thorium (Z = 90) has expected electronic configuration [Rn] 5f¹ 6d¹ 7s² and observed electronic configuration [Rn] 5f⁰ 6d² 7s² . This can be explained on the basis of extra stability of empty 5f orbital. 

The electrons are successively added to 5f subshell.

The Effects of Oxidation Reactions in Every Day Life

Corrosion

Many metals are chemically active elements and get easily affected by substances like moisture, air, acids, etc. One must have observed iron articles that are shiny when new, but get coated with a reddish brown powder when left for some time. This process is commonly known as rusting of iron. The problem with iron (as well as many other metals) is that oxidation takes place and the oxide formed does not firmly adhere to the surface of the metal causing it to flake off easily. This eventually causes structural weakness and disintegration of the metal.

Hence metal is attacked by substances around it, it is said to corrode and this process is called corrosion. Corrosion causes deterioration of essential properties in a material.

Rancidity

Have you ever tasted or smelt the fat/oil containing food materials left for a long time? This unpleasant change in the flavor and odour of a food is called rancidity. The most important cause of rancidity is the deterioration in fats and fatty foods because of oxidation process. When an oxygen atom replaces hydrogen atom in the fatty acid molecule it destabilizes the molecule. Factors which accelerate fat oxidation include, salt, light, water, bacteria, moulds trace metals (iron, zinc, etc.).

Usually substances which retard fat oxidation or rancidity are called antioxidants (such as BHT, BHA, vitamin E, and vitamin C, and spices such as sage and rosemary). These are added to foods containing fats and oil to prevent such spoiling. Keeping food in air tight containers or air tight wrapping also helps to slow down oxidation.

Functional Groups :It is an atom or group of atoms bonded together ina unique manner which is usually the site of chemical reactivity in an organic molecule. e gCH₃OH

General formula of Carboxylic acids : CnH_2n+1COOH General formula of acid chlorides :RCOCl

Ferric Thiocynate [Fe(CNS)₃]