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 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.

Multiple choice

Isobars are elements with

  1. same mass number and different atomic number

  2. same atomic number and different mass number

  3. different number of protons

  4. different number of neutrons
Reveal answer Fill a bubble to check yourself
A Correct answer
Explanation

Isobars are atoms of different chemical elements that have the same mass number but different atomic numbers. This means they have a different number of protons but the same total number of nucleons.

Multiple choice

According to Dalton

  1. molecule is indivisible

  2. atom is indivisible

  3. atoms contains charged particules

  4. atoms have mass
Reveal answer Fill a bubble to check yourself
B Correct answer
Explanation

Ans : 2.

Multiple choice

The atomic mass of an element expressed in grams is known as

  1. gram atomic mass

  2. molecular mass

  3. gram molecular mass

  4. none of these
Reveal answer Fill a bubble to check yourself
A Correct answer
Explanation

It is the quantity of an element  whose mass in grams is numerically equal to its atomic mass. In simple terms, atomic mass of an element expressed in grams is the gram atomic mass or gram atom.For example, the atomic mass of oxygen = 16 amu therefore gram atomic mass of oxygen = 16 g. The gram atom should not be confused with the mass of one atom of the element in grams, which is the actual mass of the atom.

Multiple choice

Atoms may be regarded as comprising of protons neutrons and electrons. If the mass attributed to a neutron were halved and that attributed to the electron were doubled, the atomic mass of 6C12 would

  1. remain approximately the same

  2. be approximately doubled

  3. be approximately halved

  4. be reduced approximately by 25%
Reveal answer Fill a bubble to check yourself
D Correct answer
Explanation

In 6C12 number of neutrons = 6 and protons = 6. If mass of neutron is halved, the atomic mass will now be 9, in place of initial mass 12 and reduction of 25% will be there.

Multiple choice

The atomic weight of an element is 52 and the atomic number is 24. The number of electrons, protons and neutrons in an atom of this element will be, respectively,

  1. 24, 24 and 28

  2. 24, 28 and 24

  3. 28, 24 and 24

  4. 52, 24 and 28
Reveal answer Fill a bubble to check yourself
A Correct answer
Explanation

Atomic number = Number of electrons = Number of protons Atomic weight = Number of protons + Number of neutrons The number of electrons, protons and neutrons in an atom of this element will be, respectively, 24, 24 and 28