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 nuclear reactions nuclear structure nuclei atomic nuclei physics

The binding energy of  $ _ { 17 } \mathrm { CI } ^ { 35 }$  nucleus is  $298\ \mathrm { MeV }.$  Find its atomic mass. The mass of hydrogen atom  $({ _{ 1 }{ H } }^{ 1 })$  is  $1.008143\  \mathrm { amu }$  and that of a neutron is  $1.008986\  \mathrm { amu }.$  Given  $1\  \mathrm { amu } = 931\  \mathrm { MeV }.$

  1. $148$
  2. $298$
  3. $340$
  4. $348$
Reveal answer Fill a bubble to check yourself
D Correct answer
Multiple choice nuclear reactions nuclear structure nuclei atomic nuclei physics

The atomic mass of $7 ^ { N ^ { 15 } }$ is 15.000108 a.m.u. and that  is of $8 ^ { \bigcirc ^ { 16 } }$ 15.994915 a.m.u. If the mass of a proton is 1.007825 a.m.u. then the minimum energy provided to remove the least tightly bound proton is

  1. 0.0130181 MeV

  2. 12.13 MeV

  3. 13.018 MeV

  4. 12.13 eV
Reveal answer Fill a bubble to check yourself
B Correct answer
Explanation

$\begin{array}{l} \left( { { M _{ n } }+{ M _{ H } }-{ M _{ 0 } } } \right) \times 431.5 \ =\left[ { 15.000108+1.007827-15.994915 } \right] \times 431 \ =12.13\, Mev \end{array}$

Multiple choice nuclear reactions nuclear structure nuclei atomic nuclei physics

$1$ $a.m.u$ is equivalent to 

  1. $931$ $MeV$
  2. $139$ $MeV$
  3. $93$ $MeV$
  4. $39$ $MeV$
Reveal answer Fill a bubble to check yourself
A Correct answer
Explanation

$m=1\ a.m.u.=1.66\times10^{-27}kg$

Its energy equivalent, using $E=mc^2$ is $E=1.49\times10^{-10}\ J$.
or $E=1.49\times10^{-10}/1.6\times10^{-13}\ MeV=931\ MeV$

Multiple choice nuclear reactions nuclear structure nuclei atomic nuclei physics

The mass and energy equivalent to $1 amu$ are respectively

  1. $1.67\times { 10 }^{ -27 }gm$, $9.30 MeV$
  2. $1.67\times { 10 }^{ -27 }kg$, $930 MeV$
  3. $1.67\times { 10 }^{ -27 }kg$,$ 1 MeV$
  4. $1.67\times { 10 }^{ -34 }kg$, $1 MeV$
Reveal answer Fill a bubble to check yourself
B Correct answer
Explanation

1 amu
It is defined as one twelfth of the mass of an unbound neutral atom of carbon-12 in its nuclear and electronic ground state.


Mass of 1 mole C atoms $= 12 gms$
$1\ amu = $$ \cfrac{12}{12 \times 6.023 \times 10^{23}} = 1.66 \times 10^{-27} kg$

Energy equivalent, $E = mc^2 =1.66 \times 10^{-27} kg \times (3 \times 10^8)^2$$ = 930\ MeV$

Multiple choice nuclear reactions nuclear structure nuclei atomic nuclei physics

The mass equivalent of 931.5 MeV energy is

  1. $1.66 \times 10^{-27} kg $
  2. $6.02 \times 10^{-24}kg$
  3. $1.66 \times 10^{-20} kg$
  4. $6.02 \times 10^{-27} kg$
Reveal answer Fill a bubble to check yourself
A Correct answer
Explanation
According to Einstein, mass energy equivalence is represented by
$E=m{ C }^{ 2 }$
Taking $m=1a.m.u$
$=1.66\times { 10 }^{ -27 }㎏$
and $C=3\times { 10 }^{ 8 }㎧$
We get $E=1.66\times { 10 }^{ -27 }\times { (3\times { 10 }^{ 8 }) }^{ 2 }J$
$=1.49\times { 10 }^{ -10 }J$
As $1MeV=1.6\times { 10 }^{ -13 }J$
$\therefore E=\cfrac { 1.49\times { 10 }^{ -10 } }{ 1.6\times { 10 }^{ -13 } } $
$E=931.25MeV$
Hence the mass equivalent of $931.25MeV$ energy is $1.66\times { 10 }^{ -27 }㎏$
Multiple choice

What is the overall charge of an atom?

  1. +5

  2. -5

  3. 0

  4. it depends on the atom
Reveal answer Fill a bubble to check yourself
C Correct answer
Explanation

A neutral atom has an equal number of positively charged protons and negatively charged electrons. These charges cancel each other out, resulting in a net overall charge of 0.

Multiple choice

Where is most of the mass of an atom found?

  1. electron cloud

  2. empty space

  3. nucleus

  4. protons
Reveal answer Fill a bubble to check yourself
C Correct answer
Explanation

The nucleus contains protons and neutrons, which are nearly 2000 times more massive than electrons. Consequently, virtually all of an atom's mass is concentrated in this tiny, dense central region.

Multiple choice

What does the atomic number of an atom tells you?

  1. the number of electrons

  2. the number of protons

  3. the number of neutrons

  4. the number of nucleuses
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. This number uniquely identifies the element.

Multiple choice

The number of protons in the nucleus of an atom.

  1. Atomic Number

  2. Atomic Nucleus

  3. Atomic Mass Number

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

The atomic number is the number of protons found in the nucleus of every atom of an element. It uniquely identifies a chemical element.