WORLD OF ATOMS - "Structure of nucleus"

atoms

particles properties

quantum mechanics

nucleus

radioactivity

nuclear energy

elementary particles

Nucleus
Structure
history

Library
Credits
Interactive
Guestbook

Sitemap

Structure of nucleus

History.
The Dalton atomic model suspected no nucleus. It assumed that atoms were the fundamental building blocks of nature and no particles exist that are smaller than atoms. However, Rutherford's Gold-foil experiment led him to to suspect that atoms had nuclei where most of its mass was located, and that the nucleus was positive. Bombarding Nitrogen with alpha particles, he noticed that the disintegration of the nucleus produced a positive particle equal to the mass of a hydrogen atom. He called this particle the proton and postulated that they made up the nucleus.
But a lot of positive charge concentrated in a small region would cause a lot of repulsion forces. So when Chadwick discovered the neutron in 1932, Heisenberg created the proton-neutron model of the nucleus. It also successfully explains isotopes.

The proton.
The proton is the nucleon that has a positive unit chage. Its mass is one atomic mass unit (amu, or 1.67 * 10^-27 kg, 1,836 times the mass of an electron). It is present in the nucleus of every element. Protons are responsible for the nuclear charge, the positive charge of the nucleus that deflected Rutherford's alpha particles. This charge also corresponds to the atomic number, which determines what kind of element the atom belongs to, and where on the periodic table the element belongs.

The neutron.
THe neutron is an electrically neutral particle slightly heavier than the proton. They are present in numbers greater than or equal to the number of protons in every element except Hydrogen (whose nucleus is a single proton), and variations in the number of neutrons of elements accound for isotopes.
The neutron has a maganetic moment, which suggests that its internal structure is made up of electrically charged components whose net charge is zero. The neutron is actually the fusion of a proton and an electron (since in beta decay a neutron is turned into a proton and an electron) and a neutrino.

Isotopes.
Isotopes are atoms of the same element that have differenet mass. This is explained by the proton-neutron model of the nucleus. The number of protons account for which element it is and thus how it behaves, but the number of neutrons there are determines which isotope it is, and there can be more neutrons than there are protons.
For example, elemental Hydrogen has one proton (H-1) and a mass of one amu. But an isotope of Hydrogen, deuterium, has a proton and a neutron, and a mass of two amu. As another example, Carbon-12, Carbon-13 and Carbon-14 all have 6 protons (this determines that it is Carbon atom) but have 6, 7 and 8 neutrons, respectively.
Sometimes there are too many neutrons in the nucleus. When this happens, the neutron goes under beta decay, a type of radioactive decay. The neutron splits into a proton, an electron (beta particle) and a neutrino. The proton stays in the nucleus, but the beta particle and the neutrino(an electrically neutral, light or massless particle) are emitted, and energy is released, carried by the electron (when the electron doesn't carry all the energy, the rest is carried by the neutrino).

Classification.
Nucleons are generally knoen as a baryon. Baryons are elementary particles consisting of three quarks and no antiquarks. They obey the Fermi-Dirac statistics, which encompass all elementary particles that obey the Pauli Exclusion Principle. The proton is the lightest baryon and is made of two up-quarks and one down-quark. The neutron is made of two down-quarks and one up-quark.
Nucleon's antiparticles are the antiproton and the antineutron, which have the same mass as the corresponding nucleons but opposite electric charge and magnetic moment.

ïback nextð

©ThinkQuest Team C0122360, 2001