An atom is a fragment of matter that uniquely defines achemical element. An atom is composed of a central nucleus that is usually surrounded by one or much more electrons. Every electron is negative charged. The cell nucleus is positive charged, and also contains one or an ext relatively heavy particles known as protons and neutrons.

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A proton is positively charged. The number of protons in the cell core ofan atom is the atomic number for the chemical element. A proton has actually a rest mass, denoted mp, of about 1.673 x 10-27 kilogram (kg). A ghost is electrically neutral and also has a remainder mass, denoted mn, of approximately 1.675 x 10-27 kg. The fixed of a proton or neutron increases when the bit attains excessive speed, for instance in a cyclotron or straight accelerator.

An beforehand model of the atom was occurred by the physicist ErnestRutherford in 1912. He to be the an initial to imply that atoms are favor miniature solar systems, except that the attractive force is not caused by gravity, but by opposing electrical charges. In the so-called Rutherford atom, electron orbit the cell core in one paths. Niels Bohr amendment Rutherford"s theory in 1913. In the Bohr atom,the negatively charged electrons orbit the cell core at details mediandistances. These distances are stood for by spheres, called shells, surrounding the nucleus. Electrons can move from shell to shell. Once an electron absorbs enough energy, it moves to a larger, or higher, shell. As soon as it loser a specific amount that energy, it drops to a smaller, or lower, shell.

The full mass of an atom, including the protons, neutrons andelectrons, is the atomic mass or atomic weight. Electrons contribute only a tiny component of this mass. Because that most handy purposes, the atom weight can be believed of together the variety of protons to add the variety of neutrons. Because the number ofneutrons in one atom have the right to vary, there have the right to be several different atomic weights because that mostelements.

Atoms having actually the same variety of protons, but different number ofneutrons, stand for the exact same element, however are recognized as different isotopes of that element. Theisotope for an element is mentioned by the amount of the number of protons andneutrons. Examples of different isotopes of an element are carbon 12(the most common, non-radioactive isotope that carbon) and also carbon 14 (a much less common, radiation isotope that carbon).

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Protons and also electrons have equal and also opposite charge, and normally anatom has equal number of both. Thus, atoms are usually neutral. Anion is one atomwith extra electrons or through a deficiency of electrons, causing itsbeing electrically charged. One ion with extra electron is negatively charged and is called an anion; an ion deficient in electron is positively charged and also is called a cation.