Chemistry · Physics

Atomic Structure and Mass

308 Questions

Atomic structure and mass focus on the composition of atoms, including protons, neutrons, electrons, and isotopes. This topic is essential for the chemistry sections in engineering and civil services competitive exams. Review these questions to practice calculating atomic mass, neutron count, and isotopic distributions.

Atomic mass unit calculationsNeutron and proton countsIsotopic distribution averagesLaw of triadsRest energy of atoms

Atomic Structure and Mass Questions

Multiple choice

According to Dobereiner’s law, the atomic masses of the middle elements were equal to the

  1. sum of the atomic masses of the other two elements

  2. arithmetic mean of the atomic masses of the other two elements

  3. atomic mass of the first element of the same group

  4. atomic mass of the last element of the same group
Reveal answer Fill a bubble to check yourself
B Correct answer
Explanation

The elements of the triads had similar properties and when arranged in the increasing order of atomic masses, the atomic mass of the middle element was roughly the arithmetic mean of the masses of the other two elements.

Multiple choice

The atomic and mass number of an atom of an element are 27 and 60 respectively. Which of the following statements are incorrect conclusions for the given data? (a) The name of the element is potassium. (b) It is a radioactive element. (c) The atom contains 33 neutrons in its nucleus. (d) It is a radioisotope of cobalt. (e) The ratio of neutron to the proton is less than 1.

  1. Both (a) and (b)

  2. Both (a) and (c)

  3. Only (a) and (e)

  4. Both (a) and (d)

  5. Both (b) and (c)
Reveal answer Fill a bubble to check yourself
C Correct answer
Explanation

Here, the ratio of number of neutrons to that of protons is greater than 1, which means that it is an unstable element. Hence, it is a radioisotope of cobalt.

Multiple choice

What is the valency of 52X24?
    • 2

  2. – 2
    • 1

  4. – 1
Reveal answer Fill a bubble to check yourself
A Correct answer
Explanation

Some elements, like the transition metals, have electronic configurations in which electrons from their inner shells can also be used as valence electrons; these elements can have several different oxidation states. Chromium can have a valency of +2, +3 or +6.

Multiple choice

Isotopes are

  1. atoms of the same element

  2. atoms of different elements

  3. molecules of the same element

  4. radicals of the same element

  5. atoms with the same atomic mass
Reveal answer Fill a bubble to check yourself
A Correct answer
Explanation

This is the correct answer as isotopes are atoms of the same element.

Multiple choice

Chemical identity of an atom can be changed by

  1. changing the number of protons in an atom's nucleus

  2. changing the number of neutrons in an atom's nucleus

  3. changing the number of neutrons and protons in an atom's nucleus

  4. chemical identity cannot be changed
Reveal answer Fill a bubble to check yourself
A Correct answer
Explanation

The chemical identity of an element is determined solely by its number of protons (atomic number). Changing the number of neutrons creates isotopes of the same element, while changing electrons creates ions. Only altering the proton count changes which element it is.

Multiple choice

Which of the following statements regarding helium is false?

  1. It is an inert gas.

  2. It was first discovered in the Sun then on Earth.

  3. It can form interstitial compounds.

  4. It does not have octet of electrons in its outermost shell.

  5. It is the most abundant inert gas in the atmosphere.
Reveal answer Fill a bubble to check yourself
E Correct answer
Explanation

Most abundant inert gas in the atmosphere is argon.

Multiple choice

Which of the folowing sets of quantum numbers belongs to highest energy ?

  1. n = 4 , l = 0 , m = 0 , s = + 1/ 2 .

  2. n = 3 , l = 0 , m = 0 , s = + 1/ 2 .

  3. n = 3 , l = 1 , m = 1 , s = + 1/ 2 .

  4. n = 3 , l = 2 , m = 1 , s = + 1/ 2 .
Reveal answer Fill a bubble to check yourself
D Correct answer
Explanation

this option is incorrect because , according to n+l rule , highest energy is possesed by that set which has highest value of n + l . so , in this case , n = 3 , l = 2 . hence n+l = 5 . which is not the highest among the options . hence this option is incorrect .

Multiple choice

The quantum number for the outer electrons of an atom are given by n = 2 , l = 0 , m = 0 , s = + 1 / 2 . ?

  1. lithium .

  2. beryllium .

  3. hydrogen .

  4. boron .
Reveal answer Fill a bubble to check yourself
A Correct answer
Explanation

this option is correct because , lithium has electronic configuration - 1s2 2s1 . hence according  to the question n = 2 means principle quantum number is 2  . l =0 means ' s ' orbital . s = + 1 / 2 means 1 electrons . all these characters are exhibited by lithium . therefore this option is correct .

Multiple choice

Two electrons in the same atomic orbital can be distinguished by their ?

  1. principal quantum number .

  2. orbital quantum number .

  3. magnetic quantum number .

  4. spin quantum number .
Reveal answer Fill a bubble to check yourself
D Correct answer
Explanation

this option is correct because , according to pauli exclusion principal - no two electrons in an atom can have same sets of 4 quantum number . this shows that no 2 electrons in an atom are alike or orbital can be accommodate a maximum of two electrons that too with opposite spin . hence this option is correct .

Multiple choice

The correct set of quantum number for 4d - electrons is ?

  1. n= 4 , l = 3 , m = 2 , s = +1 / 2 .

  2. n= 4 , l = 2 , m = 1 , s = 0 .

  3. n= 4 , l = 3 , m = - 2 , s = +1 / 2 .

  4. n= 4 , l = 2 , m = 1 , s = +1 / 2 .
Reveal answer Fill a bubble to check yourself
D Correct answer
Explanation

this option is correct because , l value 2 is shown by ' d ' orbital . this configuration represent an electron in 4d   orbital . hence this option is correct .