Structure Of Atom - MCQ Test (22-11-2017) - Class 9 MCQ

Electrons are present in atoms of all the elements. They are distributed around the nucleus in an atom. The charge/mass (e/m) ratio of electrons is constant in all elements. Hence, an electron is regarded as a universal particle.

The main subatomic particles of a nucleus are protons and neutrons. These are collectively called nucleons.Electrons are located in different shells outside the nucleus of an atom.

The number of protons in the nucleus of an atom is equal to its atomic number (Z). The sum of the number of protons and neutrons present in a nucleus is called the mass number (A).

Protium - an isotope of Hydrogen - does not contain any neutron in its nucleus. The nucleus of protium contains only one proton. Deutrium - another isotope of Hydrogen - contains 1 neutron in its nucleus. Tritium - another isotope of Hydrogen - contains 2 neutrons. Helium nucleus also contains 2 neutrons.

Anode rays were discovered by E. Goldstein as canal rays. These rays consist of positively charged particles. Goldstein called these positive rays as "channel rays" or "canal rays" because they were produced by the holes or channels in the cathode.

Rutherford observed that some of the αα-particles were deflected from their path after hitting the gold foil while most of the particles went straight through the gold foil.

The mass number (A) of an atom is equal to the sum of the number of protons and neutrons present in the nucleus of the atom.So, the mass number (A) of the given element = number of protons + number of neutrons = 14 +13 = 27 u

Isotopes are atoms with the same number of protons but different number of neutrons. Since the atomic number is equal to the number of protons and the atomic mass is the sum of the number of protons and neutrons, it can also be said that isotopes are atoms of the same element with the same atomic number but different mass number. They have the same chemical properties.

In his model of atom, Rutherford stated that electrons present in the extra nuclear portions are not stationary; rather they revolve around the nucleus at high speed and follow a circular path.

An atom is the smallest unit of matter. Size of an atom is very large as compared to the size of the nucleus of the atom. In an atom, the number of protons is equal to the number of electrons. Atoms are stable particles.

Atomic mass (A) of Nitrogen is 14 u and number of protons (p⁺) in the nucleus is 7. So, number of neutrons (n⁰) = Mass number (A) – number of protons (p⁺) = 14 - 7 = 7

Helium (He) has two electrons in its atom. The cation (He²⁺) is formed through the loss of 2 electrons from the outer-most shell of the atom. Hence, the number of electrons in He²⁺ will be 0

Proton is not considered as a universal particle. An electron is considered as a universal particle.

β-particles are electrons. They are deflected towards the positive electrode.

Atomic number (Z) is defined as the number of protons present in the nucleus of an atom.

An anion is formed by gaining electron(s) from other atoms. Hence, an anion contains more electrons than protons. On the other hand, a cation is formed through the loss of electron(s). A neutral atom will have the same number of negatively-charged electrons as well as positively-charged protons.

The nuclear region is a small portion of the atom as compared to the space inside an atom.

The number of electrons required to complete the octet reprersents the valency of an atom with electronegative character. The element with electronic configuration 2,8,6 will require 2 electron to achieve a stable configuration.

Electronic configuration of element X (Atomic number 16) is 2, 8, 6 and that of element Y (Atomic number 16) is 2, 8, 7. Element Y requires only one electron to complete the octet but X requires 2 electrons. So, Y will be more reactive.

The nature of cathode rays does not depend on the nature of gas taken in the cathode tube. Cathode rays travel in straight path and have energy that can rotate a light paddle wheel placed in their path.

Neils Bohr received the Noble Prize in Physics in 1922 for his work on the structure of an atom. He proposed the Bohr model of atom having discrete shells in which the electrons are distributed.

The number of electrons present in the outermost shell of an atom is called the valence electrons. Chlorine atom contains 7 electrons in the outermost shell. Chlorine ion (Cl^-) will have (7+1) electrons or 8 electrons in the outermost shell.

Magnesium (Mg) contains 12 protons (Atomic number is 12) and the mass number is 24. Number of neutrons = Mass number (A) – number of protons (Z) present in the nucleus. So, the number of neutrons = A - Z = 24 - 12 = 12

Valency is the combining capacity of an element. If an element has 8 valency then it's outer most shell has 8 electrons or noble gas configuration.

The order of shells around the nucleus is K, L, M, N from the nucleus. So, L shell is nearer to the nucleus than M shell.

Atomic number of Chlorine (Cl) is 17. Electronic configuration is 2,8,7. So, 7 electrons are present in the valence shell of Chlorine.
Atomic number of Fluorine (F) is 9. Electronic configuration is 2,7. So, 7 electrons are present in the valence shell of Fluorine.
Atomic number of Nitrogen (N) is 7. Electronic configuration is 2,5. So, 5 electrons are present in the valence shell of Nitrogen.

Electronic configuration of Carbon (C) is 2, 4. The first shell contains 2 electrons and second shell contains 4 electrons. Hence, the number of electrons in its second shell is twice the number of electrons in its first shell.

The energy of the shells increases from the inner-most to the outer-most shell. So the correct order of the energy of energy shells is K < L < M < N < O 

In Rutherford's alpha particle scattering experiment, the source of alpha particles was a Helium nucleus.

The physical state of water at 10°C is the liquid state. Below 0°Cwater in solid state and above 100°C water in the vapour state.