Chapter 4 Structure of the Atom

 Chapter 4      Structure of the Atom                                                     

**Q: Who identified the sub-atomic particle known as the electron?**

A: The electron was identified by J.J. Thomson.

**Q: Who discovered canal rays and when?**

A: E. Goldstein discovered canal rays in 1886.

**Q: What are canal rays?**

A: Canal rays are positively charged radiations found in a gas discharge, which ultimately led to the discovery of the proton.

**Q: Who was the first scientist to propose a model for the structure of an atom?**

A: J.J. Thomson was the first to propose a model for the structure of an atom.

**Q: What real-world objects did Thomson use to describe his atomic model?**

A: Thomson compared his atomic model to a Christmas pudding and a watermelon.

**Q: What particles were used in Rutherford's scattering experiment?**

A: Fast-moving alpha ($\alpha$) particles were made to fall on a thin gold foil.

**Q: What exactly are alpha ($\alpha$) particles?**

A: Alpha particles are doubly-charged helium ions that have a mass of 4 u and a considerable amount of energy.

**Q: What major discovery resulted from Rutherford's alpha-particle scattering experiment?**

A: Rutherford's experiment led to the discovery of the atomic nucleus.

**Q: What was the main drawback of Rutherford's model of the atom?**

A: It could not explain the stability of the atom, because a revolving electron would undergo acceleration, radiate energy, and eventually fall into the nucleus.

**Q: Who discovered the neutron, and in what year?**

A: J. Chadwick discovered the neutron in 1932.

**Q: Which element's atom does not contain any neutrons in its nucleus?**

A: Hydrogen is the only element whose atoms do not contain neutrons.

**Q: What formula determines the maximum number of electrons present in a specific shell?**

A: The maximum number of electrons in a shell is given by the formula $2n^2$, where 'n' is the orbit number or energy level index.

**Q: What is the maximum number of electrons that the outermost orbit of an atom can accommodate?**

A: The outermost orbit can accommodate a maximum of 8 electrons.

**Q: What are valence electrons?**

A: Valence electrons are the electrons present in the outermost shell of an atom.

**Q: How is the atomic number of an element defined?**

A: The atomic number is defined as the total number of protons present in the nucleus of an atom.

**Q: What are "nucleons"?**

A: Protons and neutrons are collectively called nucleons because they are present in the nucleus of an atom.

**Q: How do you define the mass number of an atom?**

A: The mass number is the sum of the total number of protons and neutrons present in the nucleus of an atom.

**Q: What are isotopes?**

A: Isotopes are atoms of the same element that have the same atomic number but different mass numbers.

**Q: What are the names of the three isotopes of hydrogen?**

A: The three isotopes of hydrogen are protium, deuterium, and tritium.

**Q: What are isobars?**

A: Isobars are atoms of different elements with different atomic numbers, which have the same mass number.