Previous year Atomic structure questions: ssc, rrb

Table of Contents

Introduction of Atomic strcture:-

  • Atomic structure is a fundamental concept in chemistry that forms the basis for understanding the behavior of matter at the molecular and atomic levels.
  • Knowledge of atomic structure is crucial for various competitive exams, including chemistry, physics, and engineering.

Key Concepts :


    • An atom is the smallest unit of an element that retains its chemical properties.
    • Atoms are composed of three subatomic particles: electron, proton, and neutron.

Proton(p) :-

    • Positively charged subatomic particles found in the nucleus of an atom.
    • Protons determine the element’s identity and contribute to its atomic mass.
    • Each element has a unique number of protons, known as the atomic number.

Neutron(n) :-

    • Neutrally charged subatomic particles also located in the nucleus.
    • The number of neutrons can vary within the same element, leading to isotopes with different atomic masses.

Electron(e-) :-

    • Negatively charged subatomic particles found in electron shells or energy levels surrounding the nucleus.
    • Electrons are involved in chemical reactions and determine an atom’s chemical behavior.
    • The distribution of electrons in different energy levels follows specific rules and patterns.

Atomic Number (Z):

    • The number of protons in an atom, which is unique to each element.
    • Elements are arranged in the periodic table based on their atomic numbers.

Mass Number (A):

    • The sum of protons and neutrons in the nucleus of an atom.
    • Isotopes of the same element have different mass numbers due to varying numbers of neutrons.

Electron Configuration:

Describes the arrangement of electrons in an atom’s energy levels.

Follows the Aufbau principle, Pauli exclusion principle, and Hund’s rule.

Atomic Mass:

The weighted average mass of all naturally occurring isotopes of an element.

Expressed in atomic mass units (amu) or unified atomic mass units (u).

Bohr Model:

A simplified atomic model that represents electrons in specific energy levels or orbits around the nucleus.

    • Useful for understanding atomic emission spectra.

Quantum Mechanical Model:

A more modern and accurate model that describes electrons as wave-like entities occupying orbitals in three-dimensional space.

Explains the probability of finding an electron in a specific region around the nucleus.

Periodic Table:

Organizes elements based on their atomic number and chemical properties.

Elements in the same group have similar electron configurations and exhibit similar chemical behavior.

Most important SSC atomic structure questions:

Understanding atomic structure is crucial for explaining the behavior of matter, chemical reactions, and the properties of elements.

Which among the following is present inside the nucleus of an atom?

Protons and Neutrons

just like helium nuclei

Explain- Alpha (α) particles are mainly helium
(2He4) nuclei. They are formed by two protons and
two neutrons.


Explanation: The solution of two or more components is

called homogeneous mixture. There are three types of
solution, 1- Gaseous solution 2- Liquid solution, 3-
Solid solution.

The number of protons in a Lithium nucleus is:

Lithium (Li) is a s-block element. Its atomic
number is 3. It has 3 protons in its nucleus.

The mass of an electron is nearly one upon
_ times that of a proton.

mass of electron = 1/1837 times of proton

Cathode rays are a ray of __.

Cathode rays are the stream of electrons
which move from cathode electrode to anode electrode
in the discharging tube, hence cathode rays are the
group of highly moving negative particles and these
negative particles are electrons.

The first electron shell which is the nearest to
the nucleus never holds more than ‘n’ electrons,
where ‘n’ is equal to:

The electrons in the atom revolve in different
orbits around the nucleus. Niels Bohr Bury devised
some rules to find the number of electrons in different
orbits, called as Bohr-Bury Rule. According to the Bury
rule, the number of given by electrons in an orbit is the
maximum 2n2
, where n is the number of orbitals,
For, n = 1,
⇒ 2 × (1)2
= 2

for n=2; 2n2=8
Hence, the number of electron for first shell is 2.

The size of the nucleus is approximately—-

The size of the nucleus of an atom is 10–15
meter (approximately)

What is the atomic mass of oxygen (expressed
in ‘u’)?

The atomic number of oxygen is 8 having
atomic mass of 16 u or amu.

What is the atomic number of nitrogen?

The atomic number of oxygen is 7 having
atomic mass of 14 u or amu.

The general electronic configuration ns2 np3 fits which of the following elements?

Nitrogen (N2)

Protium, deuterium and tritium are the
naturally occurring isotopes of:

Atoms having same atomic number but different mass number are known as isotopes.
Isotopes of hydrogen are protium (1H1) ,Deuterium (1H2) and Tritium (1H3) .

How many types of isotopes does Scandium

Scandium (Sc) is the element of the p-block of the periodic table, its atomic number is 21 and its
atomic weight is 44.95u It has 13 isotopes whose atomic weight varies from 40 to 52.

The existence of isotopes was first suggested in
1913 by the radiochemist ………?

Frederick Soddy

All isotopes of the same element have ——–?

Atoms of the same element whose atomic
number is similar but mass number is different, is
called as isotopes.

Atoms of different elements with different
atomic numbers, having same mass number is
known as ––––.

Elements having same mass number but
different atomic number are known as isobars.
e.g. 19K40 and 20Ca40.

Isobars have……… ?

Same mass numbers but different atomic

Which of the following is an example of pair of
Isobars ?
(a) Hydrogen and Helium
(b) Calcium and Argon
(c) Chlorine and Oxygen
(d) Oxygen and Carbon

Elements which have different atomic number but same mass number are called isobars. Since
the mass number of Argon and Calcium are same they are isomeric pairs. Both of these mass number is 40 u.

Becquerel is the unit(SI unit) of measurement of


Why do atoms make bond?

The atom make bonds to reduce potential
energy and gain stability.

……… a polar covalent bond.
(a) H-Cl (b) Ne-Ne
(c) Cl-Cl (d) Ca-Cl

Polar Covalent Bond–When covalent bond
is formed between two different atoms, e.g. HF, HCl
and the shared pair of electrons between them get
displaced more towards higher electronegativity atom.
The resultant bond is known polar covalent bond.
The shared pair of electron gets displaced move
towards chlorine since electronegativity of Cl is greater
than H.

The manufacturing of iron from iron-ore involves
the process of

The production of iron from its ore involves the process of reduction.

Sulphur and Chlorine have what type of bond?

Sulphur and Chlorine has polar covalent bond. Since electronegativity of Cl is greater than S,
the shared paired of electrons get displaced, move towards Cl.

Which of the following is a property of
(a) Forms ionic compounds
(b) Has a low melting and boiling point
(c) Reacts with water
(d) Forms covalent compounds

Ans. (d) Among the following forming covalent compounds in an appropriate property of Beryllium.

What is the net charge on Calcium fluoride?

Calcium fluoride is an inorganic element, its
chemical formula is CaF2. Its charge is 0. but individually ca and cl has +2 and -1 charge respectively.

What happens in an oxidation reaction?
(a) Protons are lost
(b) Electrons are lost
(c) Neutrons are lost
(d) Electrons are gained

Oxidation is the process of removal of electron,
hydrogen and electro positive element or group and
additon of oxygen and electro negative element or

Which among the following will be a negative
(a) If it has more electrons than protons
(b) If it has more electrons than neutrons
(c) If it has more protons than electrons
(d) If it has more protons than neutrons

(a) If it has more electrons than protons

What must be the condition for rusting in iron?
(a) Absence of O2 (b) Presence of CO2
(c) Absence of H2O (d) Presence of O2

(d) : Corrosion of iron is called rusting. Corrosion
occures when metal formed metal oxide. Thus oxygen
gas must need for rusting. Corrosion accelerated due to
the presence of moisture in atmosphere, Hydrated iron
oxide is known as rust.

Which among the following is a cation ?
(a) Aluminium (b) Iodide
(c) Chloride (d) Fluoride

Ans(a) aluminium

Cation:- The ions have positive charge is
called as “cation”.
Eg- NH4+, Ca++, Al3+, H3O+
Anion:– The ions have negative charge is called as
“anions”. Eg- Br–, I–, Cl–, OH–


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