Explore topic-wise InterviewSolutions in .

The region of space around the nucleus where the probability of finding electron is maximum is called orbital. Whereas orbit is the path of the electron around the nucleus.

These two are differentiated like this

W= pxt 

W=25 x 1 J

 n = w/hc/ ʎ 

=25x 0.75 x10^-6 /6.626x 10^-34x 3x 10⁸ 

=7.18 x 10¹⁹

(i) It could not explain the spectrum of multi-electron atoms. 

(ii) It could not explain the splitting of spectral lines in the presence of magnetic field (Zeeman effect) and electric field (Stark effect)

1. Electrons revolve around the nucleus only in certain permissible circular orbits, (orbit is some times called a shell. The first 

2. shell nearest to the nucleus is called ‘K.’ shell. The subsequent shells as we move away from the nucleus are L, M, N, O,., respectively). 

3. Electrons in each shell have been associated with a definite amount of energy. Electrons in higher shell have more energy than those nearer to the nucleus. 

4. The energy of an electron remains constant so long as it revolves in its own shell. The shells also represent energy levels.

(a) For radius- r= 52.9 n² pm 

(b) Angular Momentum – mvr= nh/2π 

(c) Energy of photon- E= -2.18 x 10^-18 / n² j

1. Not explained spectra of atoms containing more than one electrons.

2. Not explained fine spectra (when spectroscopy of high resolving power is used, it is found that each line in the ordinary specrum spilts into number of components differing in frequency). 

3. Not given explanation regarding Stark effect (splitting of spectral line in electric field) and Zeeman Effect (splitting of spectral fine in magnetic field).

Correct option is b. \(\frac{2.5h}{\pi}\)

Black body: The ideal body, which emits and absorbs radiations of all frequencies, is called a black body 

Black body radiation: The radiation emitted by such a body is called black body radiation.

Quantisation refers to light behaving as quanta or photon, which is like a packet of energy. A quanta carries an energy that is dependent on frequency and Planck's constant.

The frequency of radiation absorbed or emitted when transition occurs between two stationary states that differ in energy by ∆E, is given by –

v = \(\frac{\Delta E}{h}=\frac{E_2-E_1}{h}\)

Where E₁ and E₂ are the energies of the power and higher allowed energy states respectively.

h = Planck’s Constant

Kinetic energy of electron moving at velocity (v)

= \(\frac{1}{2}\)mv²

Where m = mass of electron

i. It does not explain spectra of atoms having more than one electron.

ii. It does not explain Zeeman‟s effect (splitting of spectral lines in magnetic field) and Stark effect (splitting of spectral lines in electric field).

iii. It is contrary to Heisenberg‟s uncertainty principle.

iv. It could not explain the ability of atom to form molecules by chemical bonds.

i. Electrons revolve around the nucleus in certain circular paths called orbits or energy levels which are named as K, L, M, N etc.

ii. Only those orbits are possible in which angular momentum is an integral multiple of h/2πwhere h is Planck‟s constant.

iii. As long as electrons revolve in a particular orbit, it does not emit or absorb energy

 iv. If an electron jumps from higher to lower energy level, energy is emitted and when electron jumps from lower to higher energy level energy is absorbed. 

(i) The electron in the atom can move around the nucleus in a circular path of fixed radius and energy. These paths are called orbits, stationary states or allowed energy states. These orbits are arranged concentrically around the nucleus. Radiation can occur only when the electron jump from one orbit to another. The atom will be completely stable in the state with the smallest orbit, since there is not orbit of lower energy into which the electron can jump.

(ii) According to Bohr's model, radiation (energy) is absorbed if the electron moves from the orbit of smaller Principal quantum number to the orbit of higher Principal quantum number, whereas the radiation (energy) is emitted if the electron moves from higher orbit to lower orbit. It explains the origin of spectral lines in H-atom.

The postulates of Bohr’s atomic model (for the hydrogen atom) :

1. The electron revolves with a constant speed in a circular orbit around the nucleus. The necessary centripetal force is the Coulomb force of attraction of the positive nuclear charge on the negatively charged electron. 

2. The electron can revolve without radiating energy only in certain orbits, called allowed or stable orbits, in which the angular momentum of the electron is equal to an integral multiple of h/2π, where h is Planck’s constant. 

3. Energy is radiated by the electron only when it jumps from one of its orbits to another orbit having lower energy. The energy of the quantum of electromagnetic radiation, i.e., the photon, emitted is equal to the energy difference of the two states.

The reaction in which the attacking reagent adds up to the substrate molecule without elimination of any molecule are called addition reaction.

CH ≡ CH + H₂\(\frac{Ni}{14:C}\).CH₂ = CH₂

Procedure: A piece of dry sodium is introduced into a fusion tube and heated till it melts. A drop of few crystals of the organic compound is added to the fusion tube. The mixture is fused gently on a Bunsen flame initially. The tube is then heated until red hot and plunged into in a mortar containing distilled water. The contents are ground throughly and filtered. The filtrate is known as sodium fusin extract, stock solution or Lassaigne’s extract. The filtrate is divided into three parts, which are used for the detection of nitrogen, sulphur and halogen in organic compound.

Organic compound containing phosphorous is fused with sodium peroxide. The phosphorus of the compound is oxidised to phosphate. The fused mass is extracted with water and filtered. The filtrate containing sodium phosphate is boiled with nitric acid and then treated with ammonium molybdate. A yellow solution of precipitate indicates the presence of phosphorus.

When an organic compound is present in an aqueous medium it is separated by shaking it with organic solvent in which it is more soluble than in water. The aqueous solution is mixed with organic solvent in a separating funnel and shaken for sometimes and then allowed to stand for some time .when organic solvent and water form two separate layers the lower layer is run out by opening the tap of funnel and organic layer is separated. the process is repeated several times and pure organic compound isseparated.

Nitrogen, Chlorine, Bromine, Iodine and Sulphur.

Nitro compounds (R-NO₂) and azo (-N = N-) compounds.

Functional isomerism.

Electronic configuration of element configuration of the element with atomic number 10=2,8

Vatrency: Zero.

The valency of an element is determined by the number of electrons in the outermost shell.

(i) The position of elements X in the modern periodic table is group number 17 and period number 3. The position of element Y in the modern periodic table is group number 2 and period number 4. Electronic configuration of element X = 2, 8,7.

It has 3 shells so period number 3.

Halogens are kept in group 17.

Electronic configuration of element Y = 2,8,8,2

It has 4 shells so a period number is 4.

The valence shell has 2 electrons so the group number is 2.

(ii) The formula of the compound:

Valency of element Y =2

Valency of element X=1

YX₂

Types of Elements

On the basis of electronic configuration, the elements of the periodic table are classified into:

• Noble gases

• Normal elements

• Transition elements

• Inner-transition elements

• Alkali metals

• Halogens

(a) Most reactive metal is Z because size of atom increases down a group and effective nuclear charge decreases. The attraction of nucleus on valence electrons also decreases. So, the tendency of losing electrons increases. Hence reactivity increases. 

(b) We know that electronegativity of non-metals increases from left to right in a period due to the increment of effective nuclear charge and decreases down a group due to the increment of size of atom. So, the most reactive non-metal is L. 

(c) L, Q, R, T are the elements of the halogen family. 

(d) Group 2- Magnesium (Mg) 

Group 13- Boron (B) 

Group 15- Nitrogen (N)

(i) The valency of Q is 3 as its valence shell has three electrons in it.

(ii) Elements P and Q are metals as they have 2 electrons in their valence shell and they are positively charged ions whereas elements R and S are non-metals as they gain electrons to complete their octet.

(iii) P and Q will form basic oxides as they are metals.

(a) We know that metallic character decreases from left to right in a period and metallic character increases down a group. So element C is the most metallic. 

(b) We know that the size of atom decreases from left to right in a period and size of atom increases down a group. So atom C is the largest.

(i) Valence electrons,in 'D'. = 5 and Valency of 'D' =3.

(ii) 'A' will have largest atomic radii because atomic radius decreases across a period from left to right.

(iii) 'A' will form the most basic oxide as it is most metallic.

Period - 2, Group - 17.

(Electronic configuration of element = 2,7)

Group 1 elements have 1 valence electron while

Group 2 elements have 2 valence electrons.

Both Mg and Ca belong to the same group (group II) and are capable of losing electrons which is responsible for their reactivity. Mg lies above Ca in Group II. As we move down a group, the effective nuclear charge on valence shell electrons decreases due to which losing electrons become easier. Thus Ca is more reactive than Mg.

(i) Ca is a metal because it contains 2 valence electrons. So it will lose these electrons to acquire stable noble gas electronic configuration. 

Ca20- 2, 8, 8, 2 

(ii) Yes, Ca is more reactive than Mg because the size of Ca is bigger than Mg. Due to this bigger size, the effective nuclear charge decreases so the attraction of nucleus on valence electrons decreases. So Ca will lose its valence electrons more easily than Mg. 

(iii) Ca has two valence electrons so its valency will be 2. 

(iv) Ca has two valence electrons and it will lose these two electrons so the formula of its chloride will be CaCl₂. 

(v) Ca is smaller than K because effective nuclear charge increases from left to right in a period. Due to this effective nuclear charge, the electronegativity increases and the attraction of the nucleus on valence shell electrons also increases. So the size decreases.

(i) Na/Sodium. 

Reason: The atomic size decreases from left to right due to the increase in the nuclear charge.

(ii) AI/Aluminium.

Reason: The tendency to Iose electrons decreases from left to right.

Detailed Answer:

(i) Na will have the largest atomic radius as atomic size goes on decreasing along a period from left to right. It is due to increase in nuclear charge (number of protons in the nucleus) which pulls the electrons towards it, i.e., a force of attraction between nucleus and valence electrons increases, therefore atomic size decreases. 

(ii) Al is least reactive because the reactivity of an element depends upon the ability of its atoms to donate or accept electrons. Tendency to lose electrons along a period generally decreases with decrease in atomic size, i.e., the force of attraction between the valence electrons and the nucleus increases, therefore electrons cannot be removed easily.

Atornic number of X = 2,8,7 = 17

Atomicnumber of Y = 2,8,8,3 = 21

(i) Ca = 2,8,8,2

(ii) Valence electrons in Rb = 1

(iii) Five

(iv) Metal

(v) Rb is biggest in size

(vi) Be < Mg < Ca < Rb.

(i) Lithium and sodium contain only single electrons in their valence electrons which they can readily loose to react. Due to their high reactivity with water, they are considered as active metals.

(ii) Fluorine lies above chlorine in the 17^th group. This indicates that fluorine has much higher electronegativity than chlorine due to which it tends to gain electron more easily. That’s why fluorine is more reactive than chlorine.

(a) (i) K (Potassium-2,8,8,1)

(ii) Be and Ca in the same group because both have same number of valence electrons in their outermost shell.

(b) Ca     X

Valency 2    1

Ca₁X₂ =CaX₂

(i) The electronic configuration (2, 8, 2) of the element 'M'  suggests that it belongs to group 2 and period 3 of the modern periodic table and its valency is 2.

(ii) The chemical formula of the compounds are :

M(NO₃)₂ / Mg(NO₃)₂;MSO₄/MgSO₄;M₃(PO₄)₂/Mg₃(PO₄)₂.

(iii) 'M' will form ionic compounds by losing two electrons.

Similarity : Both NaOH and CaO, when dissolved separately in water, solid NaOH dissolves releasing heat, resulting in rise in temperature. This reaction is exothermic reaction. When solid CaO dissolves in water, Ca(OH)₂ is formed, large amount of heat is evolved. This reaction is also exothermic reaction. Both reactions are combination reactions and single product is obtained.

NaOH_(s) + H₂O → NaOH_(aq) + Heat

CaO_(s) + H₂O → Ca(OH)_2(aq) + Heat

Difference:

1. Aqueous solution of NaOH is considered as a strong alkali.

2. Aqueous solution of Ca(OH)₂ is considered as a weak alkali.

The main difference between the Mendeleev’s and modern periodic law is that Mendeleev considered the properties of elements as periodic function of their atomic masses while modern periodic law considers the properties of elements as periodic function of their atomic numbers.

(i) X is a metal. Nature of its Basic.

(ii) X (NO₃)₂, XSO₄

These compounds are Ionic/electrovalent.

when the elements are arranged in the order of their increasing atomic masses, Mendeleev found that the elements with similar physical and chemical properties repeat after a definite interval. On the basis of these finding Mendeleev stated the periodic law. The physical and chemical properties of elements are a periodic function of their atomic masses.

(a) Group 1 (2, 8, 8, 1).

(b) Oxygen (X is monovalent so Y has to be divalent to form the compound X₂Y)

1. b. Cl

2. c. 7

3. c. 3

4. a. 1

5. b. 35.4

The atomic mass of sodium is the average of the atomic masses or Li and K i.e., \(\frac{6.9+39.1}{2}\) = 23.

(1) In the modern periodic table, the elements are arranged in the order of their increasing atomic number. In the modern periodic table there are seven horizontal rows called periods and eighteen vertical columns (1 to 18) called groups. The arrangement or the periods and groups results into formation of boxes. Atomic numbers are serially indicated in the upper part of these boxes.

(2) Each box represents the place for one element. Apart from these seven rows, there are two rows of elements placed separately at the bottom of the periodic table. They are lanthanides and actinides series. There are 118 boxes in the periodic table including the two series that means there are 118 places for elements in the modern periodic table.

The formation of a few elements was established experimentally very recently and thereby the modern periodic table is now completely filled with 118 elements.

(3) On the basis of the electronic configuration, the elements in the modern periodic table are divided into four blocks, viz. s-block, p-block, d-block and fblock. The s-block constitute groups 1 and 2. The groups 13 to 18 constitute the p-block. Groups 3 to 12 constitute the d-block, while the lanthanide and actinide series at the bottom form the f-block. The d-bloclçelements are called transition elements.

A zig-zag line shown in the p-block of the periodic table. This zig-zag line shows the three traditional types of elements, i.e. metals, nonmetals and metalloids. The metalloid elements lie along the border of zig-zag line. All the metals lie on the left side of the zig-zag line while all the nonmetals lie on the right side.

Let the atomic mass of C be x. As (A, B, C) is a Dobereiner’s triad, \(\frac{x+10.08}{2}\) = 12.01

∴ x = 24.02 – 10.08 = 13.94

∴ atomic mass of C = 13.94.