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

The atoms of different element which have the same mass number but different atomic number are called

  1. Isotopes

  2. Isobars

  3. Isotones

  4. None of the above
Reveal answer Fill a bubble to check yourself
B Correct answer
Explanation

Isobars are atoms of different elements with the same mass number but different atomic numbers. This means they have the same total number of nucleons (protons + neutrons) but different numbers of protons. For example, 40Ar (Argon, Z=18) and 40Ca (Calcium, Z=20) are isobars. Isotopes have the same atomic number but different mass numbers, while isotones have the same number of neutrons.

Multiple choice

Atomic number of a light element = _____________ = ______________.

  1. atomic mass and number of electrons

  2. number of electrons and number of protons

  3. protons and neutrons

  4. atomic mass and number of neutrons

  5. number of electrons and number of neutrons
Reveal answer Fill a bubble to check yourself
B Correct answer
Explanation

Yes, atomic number of a light element is equal to the number of electrons and also number of protons.

Multiple choice

The atomic number of Li is

  1. 4

  2. 3

  3. 6

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

The atomic number of Lithium (Li) is 3, which means it has 3 protons in its nucleus. This places it as the third element in the periodic table, after Hydrogen (1) and Helium (2).

Multiple choice

Isotopes differ in

  1. atomic number

  2. mass number

  3. number of protons

  4. number of electrons
Reveal answer Fill a bubble to check yourself
B Correct answer
Explanation

Isotopes are variants of a particular chemical element which differ in the mass number, although all isotopes of a given element have the same number of protons in each atom.

Multiple choice

Atomic number of an element gives _____.

  1. the number of electrons in its atom

  2. the number of nucleons in its atom

  3. the weight of the atom of the element

  4. the total number of elementary particles in its atom
Reveal answer Fill a bubble to check yourself
A Correct answer
Explanation

The atomic number equals the number of protons in the nucleus, which in a neutral atom is also the number of electrons. It does not represent nucleons (protons + neutrons), atomic weight, or total particles.