Subatomic Particles Protons, Neutrons, and Electrons in Atoms

6 Subatomic Particles Protons, Neutrons, and Electrons in Atoms 

All atoms are composed of the same subatomic particles protons, nentrons, and electrons. Protons and nentrons, as we saw earher, have nearly identical masses. In SI units, the mass of the proton is 1.67262 X 10 kg, and the mass of the neutron is 1.67493 X 10 kg. A more common unit to express these masses is the atomic mass unit (amu), defined as 1/12 the mass of a carbon atom containing six protons and six nentrons. The mass of a proton or nentron is approximately 1 amu. Electrons, by contrast, have an almost neghgible mass of 0.00091 X 10 kg or 0.00055 amu. 

A sample of matter—even a tiny sample, such as a sand grain—composed of only protons or only electrons, would have extraordinary repulsive forces inherent within it and would be unstable. Luckily, matter is not that way. Table 2.1 summarizes the properties of protons, neutrons, and electrons. 

Each element, identified by its unique atomic number, is represented with a unique chemical symbol, a one- or two-letter abbreviation listed directly below its atomic 

Each element is defined by a unique atomic number (Z), the number of protons in the nucleus of every atom of that element. 

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