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 chemistry the structure of the atom discovery of charged particles the plum pudding atom discovery of electrons and protons

The volume $(V)$ of nucleus of an atom is expressed in terms of mass no. $(A)$ of atom as :

  1. $V\propto A$
  2. $V\propto A^{1/3}$
  3. $V\propto A^2$
  4. $V\propto A^3$
Reveal answer Fill a bubble to check yourself
A Correct answer
Explanation

As we know,

$r=r _0\times A^{1/3}$   

where. A is atomic mass no. and
$\displaystyle V _n=\frac{4}{3}\pi r^3$

So, $\displaystyle V _n=\frac{4}{3}\pi[1.33\times 10^{-13}\times A^{1/3}]^3$

$\therefore V _n\propto A\propto mass :no$.

Multiple choice chemistry the structure of the atom discovery of charged particles the plum pudding atom discovery of electrons and protons

Nuclides having the same atomic and mass numbers are known as :

  1. isotones

  2. isomers

  3. isobars

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

Nuclides having the same atomic and mass numbers are known as Isomers.

An atom that has an unbalanced ratio of neutrons to protons in the nucleus seeks to become more stable. The unbalanced or unstable atom tries to become more stable by changing the number of neutrons and/or protons in the nucleus. This can happen in several ways:

  • converting neutrons to protons
  • converting protons to neutrons
  • ejecting an alpha particle (two neutrons and two protons) from the nucleus.

 Isotones :any of two or more species of atoms or nuclei that have the same number of neutrons.

Isobars are atoms of different chemical elements that have the same number of nucleons.

Isotopes are variants of a particular chemical element which differ in neutron number, and consequently in nucleon number.

Multiple choice chemistry quantitative chemistry molecular mass relative formula mass masses of atoms and molecules

The relative atomic mass of $N$ and relative molecular mass of $N _2$ are:

  1. $14, 28$
  2. $7, 14$
  3. $14, 14$
  4. $7, 28$
Reveal answer Fill a bubble to check yourself
A Correct answer
Explanation
Relative atomic mass is the ratio of the average mass of one atom of an element to one-twelfth of the mass of an atom of carbon-12.

The relative atomic mass of N is 14  and relative molecular mass of $N _2$ is 28.

Hence, option A is correct.
Multiple choice chemistry quantitative chemistry molecular mass relative formula mass masses of atoms and molecules

The element chlorine consists of mixture of 75.53% $ _{17}$Cl$^{35}$ and 24.47% $ _{17}$Cl$^{37}$ having a mass of 34.97 amu and 36.95 amu, respectively. The atomic weight of chloride is:

  1. 35.25

  2. 35.45

  3. 36.25

  4. 36.45
Reveal answer Fill a bubble to check yourself
B Correct answer
Explanation

Given - $ _{17} Cl^{35} - 75.53$% and mass of $Cl$ 34.97 amu
$ _{17} C^{37} - 24.47$% and mass of $Cl$ 36.95 amu
$\therefore $ Atomic weight of chlorine
$= \displaystyle \frac{(75.53 \times 34.97)+(24.47 \times 36.95)}{100} = \frac{3545.45}{100}$
$=35.45$

Multiple choice chemistry quantitative chemistry molecular mass relative formula mass masses of atoms and molecules

What was the need for using relative atomic mass or relative molecular mass?

  1. To round off every atomic mass as a multiple of 2

  2. To create new terminologies

  3. As the mass of atoms or molecules were small

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

Relative atomic mass or relative molecular mass was used as the mass of the atoms or molecules were very small. Therefore there was a need to be taken relative to some other elements.

Multiple choice chemistry quantitative chemistry molecular mass relative formula mass masses of atoms and molecules

The atomic mass of sodium is 23. The gram-atomic mass of sodium is _______.

  1. 23 g

  2. 46 g

  3. 42 g

  4. 11.5 g
Reveal answer Fill a bubble to check yourself
A Correct answer
Explanation

Gram atomic mass is the mass, in grams, of one mole of atoms in a monoatomic chemical element. It is numerically equal to the relative atomic mass in grams. The atomic mass of an element expressed in grams is called gram atomic mass.

$\therefore$  gram atomic mass of sodium $=23gm$

Multiple choice chemistry quantitative chemistry molecular mass relative formula mass masses of atoms and molecules

How many gram atoms are present in $256 g$ of ${ O } _{ 2 }$?

  1. $16$ gram atoms
  2. $32$ gram atoms
  3. $14$ gram atoms
  4. $36$ gram atoms
Reveal answer Fill a bubble to check yourself
A Correct answer
Explanation

Given that, 
Mass of $O _2$ = 256 g


We know that, 
Number of moles = $[{Mass/Molar mass}]$

So, 
Moles of $O _2$ = $\dfrac {256}{32} =8$ 


Number of gram atoms = Number of moles$*$Numer of atoms 

                                        = $8 \times 2=16$ gram atoms 

Thus, option A is the correct answer.

Multiple choice chemistry atom fundamental particles of an atom the structure of atoms discovery of subatomic particles

If number of electrons in an atom is 8 and number of protons is also 8, then give the atomic number of atom and the charge on the atom.

  1. (i) Atomic number = 8, (ii) Charge = 0

  2. (i) Atomic number = 4, (ii) Charge = 0

  3. (i) Atomic number = 8, (ii) Charge = +1

  4. (i) Atomic number = 4, (ii) Charge = +1
Reveal answer Fill a bubble to check yourself
A Correct answer
Explanation

Atomic number is equal to number of protons i.e. 8. Since number of protons is equal to number of electrons i.e. 8, therefore charge on the atom is 0.