Chapter 2, Problem 1MC

Summary Introduction

Introduction:

The building blocks of all the elements present in the universe are known as atoms, which are invisible to the naked eye. An atom, in turn, is composed of much smaller particles known as subatomic particles. The atom is divided into two main regions, including nucleus and a peripheral region. The subatomic particles, electrons, protons, and neutrons, are distributed in these two regions inside the atom.

Answer to Problem 1MC

Correct answer:

The nucleus containing the subatomic particles determines the mass of the atom. These subatomic particles determine the atomic number of the atom.

Explanation of Solution

Explanation for correct answers:

Option (a) is given that the atomic nucleus contains the atom’s mass. The nucleus contains the neutrons and protons, which hold the majority portion of the weight of the atom. The negatively charged electrons that move around the nucleus in their respective orbitals are nearly massless. Hence, option (a) is correct.

Option (c) is given that the subatomic particles can be ejected from the nucleus. Two forces work within an atom: electromagnetic forces between the positively charged protons and negatively charged electrons and nuclear forces between the protons and neutrons. The nuclear forces are stronger than the electromagnetic forces, which leads to the confinement of the nucleons (protons and neutrons) within the nucleus. In case the electromagnetic forces exceed the nuclear forces, the nucleons can be ejected from the nucleus. Hence, option (c) is correct.

Option (d) is given that the atomic number is determined by the subatomic particles contained within the nucleus. The atomic number is denoted by the number of protons present within the nucleus, which is unique for each element. Hence, option (d) is correct.

Explanation for incorrect answers:

Option (b) is given that the negatively charged subatomic particles are present in the nucleus. The electrons that carry the negative charge move around the nucleus in fixed orbits. The number of protons is equal to the number of electrons present in the nucleus. So, it is an incorrect option.

Option (e) is given that the subatomic particles present within the nucleus interact with other atoms. The protons that are present within the nucleus are confined in their region and do not leave the nucleus unless there are strong nuclear forces. The electrons are mainly responsible for the interaction with other atoms by either sharing or transferring electrons. So, it is an incorrect option.

Hence, options (b) and (e) are incorrect.

Conclusion

Thus, the nucleus having the protons along with the neutrons makes up the mass of the atom. These subatomic particles can also be ejected from the nucleus under certain circumstances, which ultimately leads to the decay of the atom. The atomic number depends on the number of protons present within the nucleus.