Final answer:
The subatomic particle with a mass of 1.67 x 10^-27 kg is the proton, which is significantly heavier than an electron and makes up a large part of an atom's mass.
Step-by-step explanation:
The subatomic particle that has a mass of 1.67 x 10-27 kg is the proton. This value corresponds to the mass of a single proton which is commonly expressed in atomic mass units (amu) as well. For comparison purposes, the mass of an electron is 9.11 x 10-31 kg, which is significantly lighter than that of a proton.
The mass of a neutron is very similar to that of a proton, but slightly heavier, at about 1.0087 amu. Both protons and neutrons make up the nucleus of an atom, while electrons orbit around the nucleus. The mass of protons and neutrons contributes almost all the mass of an atom because electrons have such a small mass.
The mass of the proton is a fundamental constant in physics and is crucial when calculating other properties of atoms and subatomic particles, such as kinetic energy and momentum.