Explore topic-wise InterviewSolutions in .

a) NH₃ will have larger value of a because of H – bonding. 

b) NH₃ will have larger value of b due to larger molecular size.

(a) 1^st element of 1^st group = H

Binary compound = HI

(b) 2^nd element of 2^nd group = Mg

1 ^st element of 17^th group = F

Binary compound = MgF₂

A) decreases

The horizontal rows in periodic table are called as periods. The atomic sizes decrease in a period with an increase in atomic number.

(i) ₁₂Mg = 2, 8,2 = 1s² , 2s²2p⁶ , 3s² It belongs to 3rd period and s-block.

(ii) ₂₆Fe = 2, 8, 14, 2 = 1s₂ , 2s²2p⁶ , 3s² , 3s² , 3p⁶ 3d⁶ , 4s² It belongs to 4th period and dblock.

(iii) ₂₉Cu = 2,8,18,1 = 1s² , 2s²2p⁶ , 3s²3s⁶3^d6 , 4s¹ It belong to 4th period and d-block

(iv) ₁₃Al = 2, 8, 3 = 1s² , 2s²2p⁶ , 3s² , 3p¹ It belongs to 3rd period and p-block.

A) K > Ca > Na > CZ

(a) (i) Mg is group 2 element with a valence of 2; N belongs to group 15 with a valence of 3. So, the formula of the compound formed would be Mg₃N₂.

(ii) Si is group 14 element with a valence of 4; O belongs to group 16 with a valence of 2. So, the formula of the compound formed would be SiO₂.

(b) (n-1) d^1-10 , ns^0-2

Correct option is  D) 18

(a) Halogens act as good oxidising agents on account of their high value of reduction potential, they have more tendency to attract electrons.

(b) It is due to increase in effective nuclear charge due to decrease in number of electrons but protons remain the some.

Halos – sea salt, genus – produced. So VII A (17) are obtained from nature as sea salt. So they are called halogen family.

Correct option is  A) 16

17 =halogen 

16=chalcogens

Chalcogeneous = Ore product. As the elements in group 16 (VI A) form ores with metals, they are called chalcogeneous family.

Alkali metal family, because aliquili = plant ashes. Na, K, etc. were obtained from plant ash.

Mendeleeff’s periodic table depends upon atomic weight.

Horizontal rows are periods and vertical columns are groups.

Leucippus and Democritus were the first to propose, in the fifth century B.C., that all matter is made of tiny units called atoms. The two philosophers held that these were solid particles without internal structure, and came in a variety of shapes and sizes. Intangible qualities such as taste and color, according to this theory, were made of atoms. However, Aristotle strongly opposed this idea, and the scientific community failed to pay serious attention to it for centuries.

1. In an attempt to account for the structure of line spectra, Sommerfeld modified Bohr’s atomic model by adding elliptical orbits.
2. While retaining the first of Bohr’s circular orbit as such, he added one elliptical orbit to Bohr’s second orbit, two elliptical orbits to Bohr’s third orbit etc.
3. Nucleus of the atom is one of the principal foci of these elliptical orbits because periodic motion under the influence of a central force will lead to elliptical orbits with the force situated at one of the foci.
   Merit: Bohr - Sommerfeld model successful in accounting for the fine line structure of hydrogen atomic spectra.
   Limitations :
4. This model failed to account for the atomic spectra of atoms of more than one electron.
5. It did not explain Zeeman and stark effects.

Bohr’s Model of an Atom :

Niels Bohr proposed that electrons in an atom occupy ‘stationary’ orbits (states) of fixed energy at different distances from the nucleus.
When an electron ’jumps’ from a lower energy state (ground state) to higher energy states (excited state) it absorbs energy or emits energy when such a jump occurs from a higher energy state to a lower energy state.
The energies of an electron in an atom can have only certain values E₁, E₂, E₃; that is, the energy is quantized. The states corresponding to these energies are called stationary states and the possible values of the energy are called energy levels.

J. J. Thomson described the arrangement of electrons in an atom.

Correct option is (B) \(3.0 × 10^8 m s^{-1}\)

In vacuum , the speed of all types of electromagnetic radiation is equal to \(3.0 \times 10^8 \ m/s\).  The speed of radiation depends on the medium.

Option : (B) 3.0 × 10⁸ m s^-1

The two results utilized by Neils Bohr to overcome the drawbacks of Rutherford model were :

• Wave particle duality of electromagnetic radiation
• Line emission spectra of hydrogen

The splitting of spectral lines in the presence of magnetic field is called Zeeman effect.

Modern periodic law : 

The physical and chemical properties of the elements are periodic functions of their electronic configurations.

First iron turns into red (lower energy corresponding to higher wavelength) and as the temperature rises it glows and turns into orange, yellow, blue or even white respectively (higher energy and lower wavelength).

Option : (C) Fractional distillation

When electric field and magnetic fields are perpendicular to each other and at right angles to the direction of propagation of wave is formed. Such a wave is called electromagnetic wave.

Wave particle duality of light (electromagnetic radiation) :

• Light has both particle and wave like nature. Phenomena such as diffraction and interference of light could be explained by treating light as electromagnetic wave.
• However, the black-body radiation or photoelectric effect could not be explained by wave nature of light. This could be accounted for by considering particle nature of light. Thus, both phenomena could be explained only by accepting that light has dual behaviour.
• When light interacts with matter it behaves as a stream of particles (called photons) and when light propagates, it behaves as an electromagnetic wave.

1. How is nl^x method useful. 

2. Explain the nl^x method with an example.

Azimuthal quantum number (l) :

• Azimuthal quantum number is also known as subsidiary quantum number and is represented by letter l.
• It represents the subshell to which the electron belongs. It also defines the shape of the orbital that is occupied by the electron.
• Its value depends upon the value of principal quantum number ‘n’. It can have only positive values between 0 and (n – 1).
• Atomic orbitals with the same value of ‘n’ but different values of ‘l’ constitute a subshell belonging to the shell for the given ‘n’ The azimuthal quantum number gives the number of subshells in a principal shell. The subshells have l to be 0, 1, 2,3 … which are represented by symbols s, p, d, f, … respectively

A) Pauli’s exclusion principle

1) 3d 

⇒ n + l 

⇒ 3 + 2 

⇒ 5 (energy) 4s

⇒ n + l 

⇒ 4 + 0 

⇒ 4 (energy) 

2) Hence, ‘3d’ has more (n + l) value than ‘4s’.

Number of protons in He = 2

Charge of proton is same as that of an electron

\(\therefore\) Charge on the nucleus of He-atom

= (+2) × 4.0 × 10⁻¹⁰

= 8.0 × 10⁻¹⁰ esu

Correct option is c. 6.62 x 10^-36 m

A) [Ar] 4s¹ 3d⁵ 

Correct option is c. 4, 0, 0, 1/2

Correct option is b. Directly proportional to its velocity

(i) H₂⁺ = 1,O₂⁻ = 17

(ii) (a) 3p_y 

(b) 1s

Correct option is c. 9.3 x 10^-8 m

The hydrogen bond is a weak bond. The strength of a hydrogen bond is 20–40 kJ mol^-1 as compared with strength of 200–400 kJ mol^-1 for normal covalent bonds.

Correct option is a. 89° , 117°

Whenever a substance contains a hydrogen atom linked to a highly electronegative atom N, O or F, the latter attracts the pair of electrons more and becomes slightly negative whereas the hydrogen atom becomes a slightly positive end. The negative end of the molecule is attracted by the positive end (i.e., Hydrogen atom) of the other molecule and in this way a bond is formed. Such a bond is called a hydrogen bond and is represented by a dotted line. Thus the hydrogen bond between the hydrogen atom bonded to the electronegative atom X may be represented as follows:

– – – X – H – – – X – H – – – X – H – – –

In this situation the hydrogen atom is attached simultaneously to two electronegative atoms. Hence it acts as a bridge between the two and is, therefore, called the hydrogen bridge.

In case of metals, the electrons in the outermost shell (valence electrons) are loosely bound, hence they are also called as free electrons. The remainder portion of the atom is known as Kernel (which is positively charged sphere). These positively charged spheres are packed in a regular fashion. The free electrons are mobile in nature and move from one kernel to another throughout the metal lattice. Thus the metal crystal may be pictured as an arrangement of positive ions immersed in a ‘Sea of mobile electrons’. The electrons move in such a way that they are simultaneously near to two or more kernels and bind them together. The bond thus formed between the metal atoms is known as Metallic bond. Hence a metallic bond may be defined as the bond formed as a result of simultaneous attraction of an electron by two or more than two positive ions of the metal.

(b) momentum

As both electron and photon have same deBroglie wavelength (λ = h /p), so they have the same momentum P.

(b) momentum 

Momentum, p = \(\frac{h}{λ}\) 

As both electron and proton have same λ, so they have the same momentum

(a) \(\frac{hc}{λ}\)

E = hυ = \(\frac{hc}{λ}\)

(a) 2

\(\frac{E_1}{E_2}\) = \(\frac{λ_2}{λ_1}\) = \(\frac{300}{150}\)= 2

(a) 1.4 V

eV₀ = hu – W₀ = 2eV – 0.6 eV = 1.4 eV

∴ V₀ = \(\frac{1.4eV}{e}\) = 1.4eV

The solubility of a saturated solution can be increased by increasing the temperature.

A solution in which no more solute can be dissolved at a given temperature is called saturated solution, and the amount of solute present in a saturated solution at a given temperature is called solubility. Solubility is directly proportional to temperature. So, when temperature decreases (i.e., when the saturated solution is cooled), solubility also decreases. Therefore, the solution becomes supersaturated.