When you compare the masses of electrons, protons, and neutrons, what you find is that electrons have an extremely small mass, compared to either protons or neutrons.
On the other hand, the masses of protons and neutrons are fairly similar, although technically, the mass of a neutron is slightly larger than the mass of a proton. Because protons and neutrons are so much more massive than electrons, almost all of the mass of any atom comes from the nucleus, which contains all of the neutrons and protons.
The third column shows the masses of the three subatomic particles in "atomic mass units. Negative and positive charges of equal magnitude cancel each other out. This means that the negative charge on an electron perfectly balances the positive charge on the proton.
In other words, a neutral atom must have exactly one electron for every proton. If a neutral atom has 1 proton, it must have 1 electron. If a neutral atom has 2 protons, it must have 2 electrons.
If a neutral atom has 10 protons, it must have 10 electrons. You get the idea. In order to be neutral, an atom must have the same number of electrons and protons. This page was constructed from content via the following contributor s and edited topically or extensively by the LibreTexts development team to meet platform style, presentation, and quality:. Learning Objectives Describe the locations, charges, and masses of the three main subatomic particles.
Determine the number of protons and electrons in an atom. Define atomic mass unit amu. Electrons Electrons are one of three main types of particles that make up atoms.
If an electron was the mass of a penny, a proton or a neutron would have the mass of a large bowling ball! Protons A proton is one of three main particles that make up the atom. Neutrons Atoms of all elements—except for most atoms of hydrogen—have neutrons in their nucleus. The element hydrogen has the simplest atoms, each with just one proton and one electron.
The proton forms the nucleus, while the electron orbits around it. All other elements have neutrons as well as protons in their nucleus, such as helium, which is depicted in Figure 2. The positively charged protons tend to repel each other, and the neutrons help to hold the nucleus together. The number of protons is the atomic number , and the number of protons plus neutrons is the atomic mass.
For hydrogen, the atomic mass is 1 because there is one proton and no neutrons. For helium, it is 4: two protons and two neutrons. For most of the 16 lightest elements up to oxygen the number of neutrons is equal to the number of protons. For most of the remaining elements, there are more neutrons than protons, because extra neutrons are needed to keep the nucleus together by overcoming the mutual repulsion of the increasing numbers of protons concentrated in a very small space.
For example, silicon has 14 protons and 14 neutrons. While a proton is made up of one down quark and two up quarks, the same accelerator tests found the proton was positively charged throughout, with the middle region possessing a stronger charge than the interior and exterior. Science Neutrons not so neutral after all, study says The neutron is more like an onion when it comes to electromagnetism, physicists say, with a negatively charged exterior and interior and a positively charged middle sandwiched between them.
Social Sharing. Similarly, a proton is made up of one down quark and two up quarks, not two down quarks and one up quark. Related Stories Can a new particle accelerator clear a stalemate in our understanding of the universe?
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