Which particles have approximately the same size and mass as each other?
A. Neutrons and electrons
B. Electrons and protons
C. Protons and neutrons
D. None – they are all very different in size and mass
The correct answer and explanation is:
The correct answer is C. Protons and neutrons.
Protons and neutrons are subatomic particles found in the nucleus of an atom. They have very similar masses and sizes compared to electrons, which are much smaller and lighter. Protons carry a positive electrical charge, neutrons are electrically neutral, and electrons carry a negative charge.
The mass of a proton is approximately 1.67 × 10⁻²⁷ kilograms, and the mass of a neutron is very close to this, about 1.68 × 10⁻²⁷ kilograms. Their masses are nearly equal, with the neutron being just slightly heavier. This similarity in mass is important because protons and neutrons together make up nearly all the mass of an atom’s nucleus.
On the other hand, electrons are much smaller and lighter. The mass of an electron is approximately 9.11 × 10⁻³¹ kilograms, which is about 1/1836 the mass of a proton or neutron. This huge difference in mass means electrons do not significantly contribute to the overall mass of an atom, but they are essential for chemical properties and interactions.
Regarding size, protons and neutrons are roughly the same size, around 1 femtometer (1 × 10⁻¹⁵ meters), while electrons are considered point particles with a size much smaller than protons and neutrons, effectively treated as having negligible size in most models.
Therefore, while electrons are fundamentally different in both mass and size, protons and neutrons are similar to each other in both respects. This similarity is why protons and neutrons together form the dense central nucleus, while electrons move around in a much larger volume around the nucleus.