Ernest Rutherford's gold foil experiment proved that atoms are mostly empty space. His experiment also helped to determine that the mass of an atom is highly concentrated in the nucleus of the atom. Which particle accounts for the least part of the mass of an atom? A. nucleon B. proton C. neutron D. electron

Protons are fundamental particles of an atom with a positive charge. They reside in the nucleus, the dense core at the center of an atom. Each proton has a mass of approximately 1 atomic mass unit (amu). This means that protons contribute significantly to the overall mass of the atom. The number of protons in an atom defines the element and is referred to as the atomic number. For example, hydrogen has one proton, carbon has six, and oxygen has eight. The more protons an atom has, the heavier it is. Protons also play a critical role in the structure of the nucleus, as their positive charge helps to keep the nucleus together despite the repulsive forces between the positively charged particles.

Neutrons are another key component of an atom, residing within the nucleus alongside protons. Unlike protons, neutrons have no electric charge; they are neutral. Despite this, neutrons have a similar mass to protons, approximately 1 atomic mass unit (amu). Their primary role is to add stability to the nucleus. Without neutrons, the repulsive forces between the positively charged protons would cause the nucleus to break apart. The number of neutrons can vary even among atoms of the same element, leading to different isotopes. Isotopes are variants of elements that have the same number of protons but different numbers of neutrons, resulting in differences in mass.

Electrons are much smaller particles compared to protons and neutrons and carry a negative charge. They orbit the nucleus at various energy levels, or shells, due to the attractive force from the positively charged nucleus. The mass of an electron is approximately 1/1836 of an atomic mass unit (amu), making it the least massive of the three main particles in an atom. Despite their small mass, electrons play a crucial role in chemical reactions and bonding, as they are the particles involved in interactions between atoms. The arrangement and behavior of electrons around the nucleus determine the chemical properties of an element.

The nucleus is the small, dense center of an atom, consisting of protons and neutrons. It contains nearly all the atom's mass despite occupying only a tiny fraction of the atom's volume. The nucleus is held together by the strong nuclear force, which is much stronger than the repulsive electrostatic force between protons. The number of protons in the nucleus, called the atomic number, defines the type of element. Adding up both protons and neutrons gives the atomic mass number, which influences the isotope of the element. The stability and behavior of the nucleus are central to understanding atomic structure and the properties of elements. Understanding the nucleus helps explain phenomena such as radioactivity and nuclear energy.