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 chemistry the language of chemistry percent composition percentage composition and empirical formula empirical formula, percentage composition and molecular formula water of crystallisation

From $\ 2 \ mg$ calcium $1.2\times 10^{19}$ atoms are removed. The number of $g$ - atoms of calcium left is $(Ca=40)$:

  1. $5\times 10^{-5}$
  2. $2\times 10^{-5}$
  3. $3\times 10^{-5}$
  4. $5\times 10^{-6}$
Reveal answer Fill a bubble to check yourself
C Correct answer
Explanation

$2\ mg$ Calcium moles $=\dfrac{2\times 10^{-3}}{40}=5\times 10^{-5}$


$1$ mole $=6.022\times 10^{23}$ atoms

$x=\dfrac{1.2\times 10^{19}}{6.022\times 10^{23}}$

$=1.99\times 10^{-5}$ moles removed
$\therefore$ Remaining moles $=5\times 10^{-5}-1.99\times 10^{-5}$
$=3.00\times 10^{-5}$ moles
$1\ g$ atom $=1$ mole
$\therefore$ Option $C$ correct.

Multiple choice chemistry atoms, molecules and radicals history of atomic model atomic theory of dalton daltons atomic theory

Dalton's theory of same element have same mass and properties was proved wrong with the invention of:

  1. molecules

  2. isotopes

  3. neutrons

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

According to Dalton Atomic Theory, atoms of an element are identical in mass, size and many other chemicals or physical properties. 


But, practically we observe that atoms of several elements differ in their densities and masses. 

These atoms with the different masses are known as isotopes. For example, Chlorine (Cl) has 2 isotopes with the mass numbers of 35 and 37.

Hence, the correct option is $\text{B}$

Multiple choice chemistry atoms, molecules and radicals history of atomic model atomic theory of dalton daltons atomic theory

Which of the following is not a postulate of Dalton's atomic theory? 

  1. Different elements have atoms of different masses.

  2. Atoms combine in simple whole number ratios to form compounds..

  3. Atoms are not created or destroyed in chemical change.

  4. Atoms of a single element can have different masses.
Reveal answer Fill a bubble to check yourself
D Correct answer
Explanation

Postulates of Dalton's atomic theory:

  • All matter consists of indivisible particles called atoms.
  • Atoms of the same elements are similar in shape and mass but differ from the atoms of other elements.
  • Atoms cannot be created or destroyed.
  • Atoms of different elements may combine with each other in a fixed, simple, whole number ratios to form compound atoms.
  • The atom is the smallest unit of matter that can take part in a chemical reaction.

Multiple choice gamma decay change in nucleus due to radioactive decay alpha, beta and gamma particles (rays) and their properties

The atomic masses of the hydrogen isotopes are
$m _1H^1=1.007825\ amu$
$m _1H^2=2.014102\ amu$
$m _1H^3=3.016049\ amu$
The energy released in the reaction
$ _1H^2+ _1H^2 \rightarrow _1H^3+ _1H^1$
is nearly:

  1. $1\ MeV$
  2. $2\ MeV$
  3. $4\ MeV$
  4. $8\ MeV$
Reveal answer Fill a bubble to check yourself
C Correct answer
Explanation
Mass defect: $\Delta M = 2m _1H^2 -(m _1H^1+m _1H^3)$
$\therefore$   $\Delta M = 2(2.014202)  -(1.007825+3.016049) = 4.33\times 10^{-3}$  amu
Energy released, $E = \Delta M\times 931$  $MeV$         
$\implies$   $E = 4.33\times 10^{-3}\times 931 \approx 4MeV$
Multiple choice introduction to mole gas laws and mole concept atoms and molecules chemistry mole concept chemical formula and mole concept

The number of electrons which will together weigh one gram is :

  1. $1.098 \times 10^{27}$ electrons
  2. $9.1096\times 10^{31}$ electrons

  3. 1 electrons
  4. $1\times 10^4$ electrons
Reveal answer Fill a bubble to check yourself
A Correct answer
Explanation

Mass of a electrons = $9.1096\times 10^{-31}Kg$
1g or $10^{-3}kg = \dfrac{1}{9.1096\times 10^{-31}}\times 10^{-3}$
=$1.098\times 10^{27}$ electons

Multiple choice chemistry what is inside atom discovery of neutrons structure of atoms discovery of subatomic particles

The mass of an atom is : 

  1. the sum of the masses of protons and electrons present in the nucleus.

  2. equal to the mass of neutrons in the nucleus.

  3. the sum of the masses of protons and neutrons present in the nucleus.

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

The mass of an atom is given by the sum of the masses of protons and neutrons present in the nucleus.

Multiple choice chemistry what is inside atom discovery of neutrons structure of atoms discovery of subatomic particles

A neutral atom of an element with nuclear charge 11 times and mass 23 times that of hydrogen. Find the ratio of electrons to protons present in its stable ion.

  1. 1:1

  2. 5:6

  3. 10:11

  4. 12:11
Reveal answer Fill a bubble to check yourself
C Correct answer
Explanation

Protons in neutral atom = nuclear charge = 11

Electrons in neutral atom = 11
Mass = 23 

Element = Sodium
Ion = $Na^+$
Electrons in ion = 11-1 = 10
Protons in ion = 11
Ratio of electron to proton = 10:11

Multiple choice chemistry what is inside atom discovery of neutrons structure of atoms discovery of subatomic particles

Who determined the mass of a neutron?

  1. John Dalton (early 1800's)

  2. Ernest Rutherford (1911)

  3. Niels Bohr (1913)

  4. James Chadwick (1932)
Reveal answer Fill a bubble to check yourself
D Correct answer
Explanation

The presence of neutron and its mass was determined by James Chadwick. Neutron was discovered by bombarding $\alpha-$particles on $Be$. On doing so, highly energetic beam of radiation was observed by Chadwick. Thus mass of neutron was determined by James Chadwick.

Multiple choice chemistry introduction to analytical chemistry interpreting a balanced chemical reaction percentage yield stoichiometric calculations

Percentage purity of a sample of gold is $$. How many atoms of gold are present in its $1$ gram
(Atomic mass of gold =$197 u.) 

  1. $2.6*{10^{21}}$
  2. $2.6*{10^{23}}$
  3. $3.0*{10^{21}}$
  4. $4.5*{10^{20}}$
Reveal answer Fill a bubble to check yourself
A Correct answer
Explanation

Assuming 100% purity, 1 g gold = 1/197 mol. Atoms = (1/197) * 6.022 * 10^23 = 3.05 * 10^21. The provided answer 2.6 * 10^21 implies a purity of ~85%.

Multiple choice physics some natural phenomena how lightning occurs? the story of lightning advanced of lightning

There are $4\times 10^{23}$ atoms in a metal sphere. If one electron is removed from 0.1% atom. what will be the charge on the sphere?

  1. $64C$
  2. $6.4C$
  3. $0.64C$
  4. $-6.4C$
Reveal answer Fill a bubble to check yourself
A Correct answer
Explanation

Total atoms = 4 x 10^23. Atoms with an electron removed = 0.1% of 4 x 10^23 = 4 x 10^20. Charge = (number of electrons) x (charge per electron) = (4 x 10^20) x (1.6 x 10^-19 C) = 64 C.

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.