i. Identify the ion from the given figure.
ii. Write the electronic configuration of the ion and atom mentioned in the figure.
iii. How do we get the number of protons as 12?
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Answers
Answer:
Q1. Compare the properties of electrons, protons and neutrons.
Ans.
Q2. What are the limitations of J.J. Thomson’s model of the atom?
Ans. According to J.J. Thomson’s model of an atom, the electrons are embedded all over in the positively charged spheres. But experiments done by other scientists showed that protons are present only in the centre of the atom and electrons are distributed around it.
Q3. What are the limitations of Rutherford’s model of the atom?
Ans. According to Rutherford’s model of an atom the electrons are revolving in a circular orbit around the nucleus. Any such particle that revolves would undergo acceleration and radiate energy. The revolving electron would lose its energy and finally fall into the nucleus, the atom would be highly unstable.
But we know that atoms are quite stable.
Q4. Describe Bohr’s model of the atom.
Ans. Bohr’s model of the atom
(1) Atom has nucleus in the centre.
(2) Electrons revolve around the nucleus.
(3) Certain special orbits known as discrete orbits of electrons, are allowed inside the atom.
(4) While revolving in discrete orbits the electrons do not radiate energy.
(5) These orbits or shells are called energy levels.
(6) These orbits or shells are represented by the letters K, L, M, N or the numbers n = 1, 2, 3, 4
Q5. Compare all the proposed Bohr’s models of an atom given in this chapter.
Ans.
Q6. Summarise the rules for writing of distribution of electrons in various shells for the first eighteen elements.
Ans. The rules for writing of distribution of electrons in various shells for the first eighteen elements are:
(i) The maximum number of electrons present in a shell is formula—2n2
n = orbit number i.e., 1, 2, 3
Maximum number of electrons in different shells are:
K shell n = 1 2n2 ⇒ 2(1)2 = 2
L shell n = 2 2n2 ⇒ 2(2)2 = 8
M shell n = 3 2n2 ⇒ 2(3)2 = 18
N shell n = 4 2n2 ⇒ 2(4)2 = 32
(ii) The maximum number of electrons that can be accommodated in the outermost orbit is 8.
(iii) Electrons are not accommodated in a given shell unless the inner shells are filled. (Shells are filled step-wise).
Q7. Define valency by taking examples of silicon and oxygen.
Ans. Valency is the combining capacity of an atom.
Atomic number of oxygen = 8
Atomic number of silicon = 14
K L M
Electronic configuration of oxygen = 2 6 –
Electronic configuration of silicon = 2 8 4
In the atoms of oxygen the valence electrons are 6 (i.e., electrons in the outermost shell). To fill the orbit, 2 electrons are required. In the atom of silicon, the valence electrons are 4. To fill this orbit 4 electrons are required.
Hence, the combining capacity of oxygen is 2 and of silicon is 4.
i.e., Valency of oxygen = 2
Valency of silicon = 4
Q8. Explain with examples:
(i) Atomic number (ii) Mass number,
(iii) Isotopes and (iv) Isobars.
Give any two uses of isotopes.
Ans. (i) Atomic number: The atomic number of an element is equal to the number of protons in the nucleus of its atom.
e.g., Oxygen has 6 protons hence atomic no. = 6.
(ii) Maas number: The mass number of an atom is equal to the number of protons and neutrons in its nucleus.
Nucleons = number of protons + number of neutrons
Example: Protons + Neutrons = Nucleus = Mass number
6 + 6 = 12
(iii)Isotopes: Isotopes are atoms of the same element which have different mass number but same atomic number.
(iv)Isobars: Isobars are atoms having the same mass number but riifteren atomic numbers.
Both calcium and argon have same mass number but different storm number.
Two uses of isotopes are:
(i) An isotope of iodine is used in the treatment of goitre.
(ii) An isotope of uranium is used as a fuel in nuclear reactors.
Answer:
1.Mg has a 12 atomic number, hence there are two 2, 8, 2 is how the electronics are set up.
It gives up two electrons and creates the Mg cation in order to acquire a stable electrical configuration of eight.
Hence, ion's electrical configuration would be 2, 8 in this case.
3. The atomic number of the element is the same as the number of protons.
The distribution of electrons within an atom, molecule, or other physical structure in their respective orbitals is known as the electron configuration in atomic physics and quantum chemistry.
As an illustration, the neon atom's electron configuration is 1s2 2s2 2p6, which means that 1, 2 and 6 electrons, respectively, are present in each of the subshells of the first two atoms.
Each electron is said to move independently in an orbital, in electronic setups.
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