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

Electron affinity is positive when

  1. O- is formed from O

  2. O2- is formed from O

  3. O+ is formed from O

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

Oxygen needs two electrons to complete its octet. So, electron affinity is positive when O2- is formed from O.

Multiple choice

An element with atomic number 13 has

  1. 13 neutrons in the nucleus

  2. three valence electrons

  3. 13 electrons in the valence shell

  4. three unpaired electrons
Reveal answer Fill a bubble to check yourself
B Correct answer
Explanation

An element with atomic number 13 has electronic configuration as 1s2, 2s2, 2p6, 3s2, 3p1. So it has 3 electrons in the valence shell.

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.

Multiple choice

Which of the following does not admit any division?

  1. Atom

  2. Molecules

  3. Compounds

  4. All of these
Reveal answer Fill a bubble to check yourself
A Correct answer
Explanation

According to Dalton's atomic theory, the atom is the smallest indivisible unit of matter that cannot be divided further by chemical means. While modern physics has identified subatomic particles like protons and electrons, in the context of basic chemical units, the atom is considered the fundamental building block. Molecules and compounds are composed of multiple atoms and can be divided.

Multiple choice

Which of the statements is/are correct? A. Cr2+ ions are unstable in aqueous solution. B. Energy of 3d and 4s orbitals are the same for a hydrogen atom. C. Degenerate orbitals possess different energies.

  1. Only A

  2. Only B

  3. Only C

  4. Only A and B

  5. Only A and C
Reveal answer Fill a bubble to check yourself
D Correct answer
Explanation

Cr2+ ions are unstable in aqueous solution, i.e highly reactive in aqueous solution. It is a correct statement. Energy of 3d and 4s orbitals are the same for a hydrogen atom.

Multiple choice

The atomic number of an element is equal to the

  1. number of neutrons in its nucleus

  2. number of protons in its nucleus

  3. relative atomic mass

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

The atomic number is defined as the number of protons in the nucleus of an atom, which uniquely identifies the element.