Chemistry · Physics

Atomic Structure and Mass

277 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

Write no. of protons in carbon?

  1. 7

  2. 6

  3. 9

  4. 8
Reveal answer Fill a bubble to check yourself
B Correct answer
Explanation

The atomic number of carbon is 6, which indicates that a neutral carbon atom has 6 protons in its nucleus.

Multiple choice

In case of the triad containing the elements Ba, Ca and Sr, which of the following statements is correct?

  1. The atomic mass of Ba is roughly the average of the atomic masses of the other two elements.

  2. The atomic mass of Sr is roughly the average of the atomic masses of the other two elements.

  3. The atomic mass of Ba is less than the average of the atomic masses of the other two elements.

  4. The atomic mass of Sr is more than the average of the atomic masses of the other two elements.
Reveal answer Fill a bubble to check yourself
B Correct answer
Explanation

According to the definition of Dobereiner's law of triads, (the atomic mass of the middle element was roughly the average of the atomic masses of the other two elements) the statement (2) is correct.  

Multiple choice

Which elementary particles are equal in mass?

  1. Neutron & proton

  2. electron & proton

  3. neutron & electron

  4. none
Reveal answer Fill a bubble to check yourself
A Correct answer
Explanation

Protons and neutrons are both nucleons and have nearly identical masses, approximately 1 atomic mass unit each, whereas electrons are significantly lighter.

Multiple choice

92X238 emits 5 α and 6 β particles, the product Y has the atomic number and mass number of _______ respectively.

  1. 90 and 218

  2. 82 and 218

  3. 88 and 218

  4. 88 and 230

  5. 84 and 222
Reveal answer Fill a bubble to check yourself
C Correct answer
Explanation

92X238 → 88Y218 Change in mass number = 238 - 218 = 20 The mass number changes only because of α-particle emission Hence, number of α-particles emitted = 20/4 = 5 After emission of 5 α-particles, the atomic number should change by 2 x 5 = 10 Actual change in atomic number = 92 - 88 = 4 Hence, number of β-particles emitted = 10 – 4 = 6 After emission of 5 α and 6β particles from 92X238, product formed is 88Y218. Atomic number of product = 88 Mass number of product = 218

Multiple choice

Mass number is the sum of ________ and ________ present in an atom.

  1. protons and electrons

  2. electrons and neutrons

  3. protons and neutrons

  4. electrons and positron

Reveal answer Fill a bubble to check yourself
C Correct answer
Explanation

The mass number of an atom is defined as the total number of protons and neutrons in its nucleus. Electrons have negligible mass compared to protons and neutrons.

Multiple choice

Atomic number is always _______ as that of atomic mass.

  1. same

  2. lesser than or equal

  3. greater

  4. lesser
Reveal answer Fill a bubble to check yourself
B Correct answer
Explanation

The atomic mass (protons + neutrons) is always greater than or equal to the atomic number (protons only). For hydrogen, they are equal; for all other elements, the mass is greater.