Complete the following table.

[question] Question. [/question] [solution] Solution: [/solution]...

Which one of the following is a correct

[question] Question. Which one of the following is a correct electronic configuration of sodium? (a) 2,8 (b) $8,2,1$ (c) $2,1,8$ (d) $2,8,1$ [/question] [solution] Solution: (d) [/solution]...

Choose the correct answer :

[question] Question. Choose the correct answer : Number of valence electrons in $\mathrm{Cl}^{-}$ion are (a) 16 (b) 8 (c) 17 (d) 18 [/question] [solution] Solution: (b) [/solution]...

Choose the correct answer :

[question] Question. Choose the correct answer : Isotopes of an element have (a) The same physical properties (b) Different chemical properties (c) Different number of neutrons (d) Different atomic numbers [/question] [solution] Solution: (c) [/solution]...

Choose the correct answer :

[question] Question. Choose the correct answer : Rutherford’s alpha-particle scattering experiment was responsible for the discovery of (a) Atomic nucleus (b) Electron (c) Proton (d) Neutron [/question] [solution] Solution: (a) [/solution]...

For the following statements,

[question] Question. For the following statements, write T for ‘True’ and F for ‘False’. (a) J.J. Thomson proposed that the nucleus of an atom contains only nucleons. (b) A neutron is formed by an electron and a proton combining together. Therefore, it is neutral. (c) The mass of an electron is about $\frac{1}{2000}$ times that of proton. (d) An isotope of iodine is used for making tincture iodine, which is used as a medicine. [/question] [solution] Solution: (a) (F) (b) (F) (c) (T) (d) (F) [/so...

Composition of the nuclei of two atomic

[question] Question. Composition of the nuclei of two atomic species X and Y are given as under Give the mass numbers of X and Y. What is the relation between the two species? [question] [solution] Solution: Mass number of X = Number of protons + Number of neutrons = 6 + 6 = 12 Mass number of Y = Number of protons + Number of neutrons = 6 + 8 = 14 These two atomic species X and Y have the same atomic number, but different mass numbers. Hence, they are isotopes. [/solution]...

If Z = 3, what would be the valency of the element?

[question] Question. If Z = 3, what would be the valency of the element? Also, name the element. [/question] [solution] Solution: By Z = 3, we mean that the atomic number of the element is 3. Its electronic configuration is 2, 1. Hence, the valency of the element is 1 (since the outermost shell has only one electron). Therefore, the element with Z = 3 is lithium. [/solution]...

The average atomic mass of a sample of an element X is

[question] Question. The average atomic mass of a sample of an element $X$ is $16.2 \mathrm{u}$. What are the percentages of isotopes ${ }_{8}^{16} \mathrm{X}$ and ${ }_{8}^{18} \mathrm{X}$ in the sample? [/question] [solution] Solution: Suppose percentage of isotope ${ }_{8}^{16} \mathrm{X}=\mathrm{x}$ Then percentage of isotope ${ }_{8}^{18} \mathrm{X}=(100-\mathrm{x})$ $\therefore$ Average atomic mass $=\frac{16 \times x+18(100-x)}{100}$ $=\frac{1800-2 x}{100}=18-0.02 x$ $\therefore 18-0.02 \...

The average atomic mass of a sample of an element

[question] Question. The average atomic mass of a sample of an element $\mathrm{X}$ is $16.2 \mathrm{u}$. What are the percentages of isotopes ${ }_{8}^{16} \mathrm{X}$ and ${ }_{8}^{18} \mathrm{X}$ in the sample? [/question] [solution] Solution: Suppose percentage of isotope ${ }_{8}^{16} \mathrm{X}=\mathrm{x}$ Then percentage of isotope ${ }_{8}^{18} \mathrm{X}=(100-\mathrm{x})$ $\therefore$ Average atomic mass $=\frac{16 \times x+18(100-x)}{100}$ $=\frac{1800-2 x}{100}=18-0.02 x$ $\therefore ...

If bromine atom is available in the form

[question] Question. If bromine atom is available in the form of $\mathrm{Br}^{79}, \mathrm{Br}^{81}$, say, two isotopes $(49.7 \%)$ and $(50.3 \%)$, calculate the average atomic mass of bromine atom. [/question] [solution] Solution: It is given that two isotopes of bromine are $(49.7 \%)$ and $(50.3 \%) .$ Then, the average atomic mass of bromine atom is given by : $\therefore$ Average atomic mass of Br $=\frac{49.7 \times 79+50.3 \times 81}{100}=\frac{3926.3+4074.3}{100}$ $=39.263+40.743=80.00...

$\mathrm{Na}^{+}$has completely filled $\mathrm{K}$ and $\mathrm{L}$ shells. Explain.

[question] Question. $\mathrm{Na}^{+}$has completely filled $\mathrm{K}$ and $\mathrm{L}$ shells. Explain. [/question] [solution] Solution: An atom of Na has a total of 11 electrons. Its electronic configuration is $2,8,1 .$ But, $\mathrm{Na}^{+}$ion has one electron less than Na atom i.e., it has 10 electrons. Therefore, 2 electrons go to $\mathrm{K}$-shell and 8 electrons go to $\mathrm{L}$-shell, thereby completely filling $\mathrm{K}$ and $\mathrm{L}$ shells. [/solution]...

Explain with examples

[question] Question. Explain with examples (i) Atomic number, (ii) Mass number, (iii) Isotopes and (iv) Isobars. Give any two uses of isotopes. [/question] [solution] Solution: (i) Atomic number The atomic number of an element is the total number of protons present in the atom of that element. For example, nitrogen has 7 protons in its atom. Thus, the atomic number of nitrogen is 7. (ii) Mass numbers The mass number of an element is the sum of the number of protons and neutrons present in the at...

Define valency by taking examples of silicon and oxygen

[question] Question. Define valency by taking examples of silicon and oxygen [/question] [solution] Solution: The valency of an element is the combining capacity of that element. The valency of an element is determined by the number of valence electrons present in the atom of that element. If the number of valence electrons of the atom of an element is less than or equal to four, then the valency of that element is equal to the number of valence electrons. For example, the atom of silicon has fo...

Summarize the rules for writing of distribution

[question] Question. Summarize the rules for writing of distribution of electrons in various shells for the first eighteen elements. [/question] [solution] Solution: The rules for writing of the distribution of electrons in various shells for the first eighteen elements are given below. (i) The maximum number of electrons that a shell can accommodate is given by the formula $' 2 n^{2}$ ', where ' $n$ ' is the orbit number or energy level index $(n=1,2,3 \ldots)$ The maximum number of electrons p...

Compare all the proposed models

[question] Question. Compare all the proposed models of an atom given in this chapter. Thomson’s model Rutherford’s model Bohr’s model [/question] [solution] Solution: An atom consists of a positively charged sphere with electrons embedded in it. An atom consists of a positively charged particles concentrated at the centre known as the nucleus. The size of the nucleus is very small as compared to the size of the atom. The electrons revolve around the nucleus in well-defined orbits. There are onl...

Describe Bohr’s model of the atom.

[question] Question. Describe Bohr’s model of the atom. [/question] [solution] Solution: Bohr’s model of the atom Neils Bohr proposed the following postulates regarding the model of the atom. (i) Only certain orbits known as discrete orbits of electrons are allowed inside the atom. (ii) While revolving in these discrete orbits, the electrons do not radiate energy. These discrete orbits or shells are shown in the following diagram. The first orbit (i.e., for n = 1) is represented by letter K. Sim...

What are the limitations

[question] Question. What are the limitations of Rutherford’s model of the atom? [/question] [solution] Solution: A model of the atom was described by the British physicist Ernest Rutherford in 1911, and is known as the Solar System model. It is very simple, and is still used to teach elementary atomic structure to school children. • An atom consists of a central nucleus. This nucleus is composed of positively charged protons, and electrically uncharged (neutral) neutrons. • Negatively charged e...

What are the limitations of J.J

[question] Question. What are the limitations of J.J. Thomson’s model of the atom? [/question] [solution] Solution: According to J.J. Thomson’s model of an atom, an atom consists of a positively charged sphere with electrons embedded in it. However, it was later found that the positively charged particles reside at the centre of the atom called the nucleus, and the electrons revolve around the nucleus. [/solution]...

Compare the properties of electrons

[question] Question. Compare the properties of electrons, protons and neutrons. [/question] [solution] Solution: Electron (i) Electrons are present outside the nucleus of an atom. (ii) Electrons are negatively charged. (iii) The mass of an electron is considered to be negligible. Proton (i) Protons are present in the nucleus of an atom. (ii) Protons are positively charged. (iii) The mass of a proton is approximately 2000 times as the mass of an electron Neutron (i) Neutrons are present in the nu...

Write the electronic configuration

[question] Question. Write the electronic configuration of any one pair of isotopes and isobars. [/question] [solution] Solution: ${ }_{6}^{12} \mathrm{C}$ and ${ }_{6}^{14} \mathrm{C}$ are isotopes, have the same electronic configuration as $(2,4)$. ${ }_{20}^{40} \mathrm{Ca}$ and ${ }_{18}^{40} \mathrm{Ar}$ are isobars. They have different electronic configuration as given below: ${ }_{20}^{40} \mathrm{Ca}-2,8,8,2$ ${ }_{18}^{40} \mathrm{Ar}-2,8,8$ [/solution]...

For the symbol H

[question] Question. For the symbol H, D and T tabulate three sub-atomic particles found in each of them. [/question] [solution] Solution: [/solution]...

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