Structure Of Atoms - Class 9 MCQ

As the configuration of ion is asked, Mg forms ion Mg²⁺ after losing 2 electrons and so its electronic configuration is 2, 8.

The Plum Pudding Model:
The Plum Pudding Model, also known as the Thomson Model, was proposed by J.J. Thomson in the early 20th century to explain the structure of atoms. Here is a detailed explanation of the model:
1. Background:
- Before the Plum Pudding Model, the prevailing theory was the Rutherford Model proposed by Ernest Rutherford.
- According to Rutherford's model, atoms consisted of a small, dense, positively charged nucleus surrounded by orbiting electrons.
2. Description of the Plum Pudding Model:
- J.J. Thomson proposed an alternative model based on his experiments on cathode rays.
- According to Thomson's model, an atom is a positively charged sphere with negatively charged electrons embedded in it.
- The positive charge is distributed uniformly throughout the atom, similar to the distribution of raisins in a plum pudding or chocolate chip cookies.
3. Key Points of the Plum Pudding Model:
- The atom is electrically neutral because the positive and negative charges balance each other out.
- The electrons are distributed throughout the atom, providing stability to the structure.
- The positive charge is spread out, preventing the electrons from being pulled into the nucleus.
- This model provided an explanation for the observed stability and lack of collapse of the atom.
4. Experimental Evidence and Challenges:
- Thomson's model was based on his experiments on cathode rays, which showed that electrons were negatively charged particles.
- However, later experiments performed by Rutherford and his colleagues disproved the Plum Pudding Model.
- The Rutherford Scattering Experiment showed that the positive charge of an atom was concentrated in a small, dense nucleus, rather than being spread out.
Conclusion:
- The Plum Pudding Model proposed by J.J. Thomson was an important step in the development of atomic theory.
- While it was eventually disproven, it provided insights into the distribution of charge and the stability of atoms.
- The model was an important stepping stone towards the understanding of atomic structure that we have today.

Bohr proposed the 2n^2 rule.
Explanation:
- The 2n^2 rule, also known as the Bohr's rule, was proposed by Niels Bohr, a Danish physicist, in 1913.
- The rule states that the maximum number of electrons that can occupy a specific energy level or shell is given by the formula 2n^2, where 'n' represents the principal quantum number of the energy level.
- The principal quantum number represents the energy level or shell number, starting from 1 for the innermost shell.
- According to the 2n^2 rule, the first energy level or shell (n=1) can hold a maximum of 2 electrons, the second energy level (n=2) can hold a maximum of 8 electrons, the third energy level (n=3) can hold a maximum of 18 electrons, and so on.
- This rule is a simplified way to understand the electron configuration and distribution in atoms, providing a framework for the periodic table and chemical bonding.
- The 2n^2 rule is a fundamental concept in atomic physics and is still used today to explain the behavior of electrons in atoms.

It emmits gamma rays which destroys cancer cells

Isobars are atoms (nuclides) of different chemical elements that have the same number of nucleons. Correspondingly, isobars differ in atomic number (or number of protons) but have the same mass number