ATOMIC MASS UNIT
Nevertheless, the nucleus contains essentially all of the mass of the atom. In order to discuss the mass of an atom we need to define a new unit of mass appropriate to that of an atom. This new unit of mass is called the "atomic mass unit" or amu. The conversion between the amu and gram is
1 amu = 1.67x10-24 g
The mass, in amu, of the three particles is given in the table below:
Note that the mass of an electron is about 2000 times smaller than that of the proton and neutron. Also note that the mass of the proton and neutron is close to 1 amu. This is a useful fact to remember. If the number of electrons does not equal the number of protons in the nucleus then the atom is an ion:
cation: number of electrons < number of protons
anion: number of electrons > number of protons
Nevertheless, the nucleus contains essentially all of the mass of the atom. In order to discuss the mass of an atom we need to define a new unit of mass appropriate to that of an atom. This new unit of mass is called the "atomic mass unit" or amu. The conversion between the amu and gram is
The mass, in amu, of the three particles is given in the table below:
Note that the mass of an electron is about 2000 times smaller than that of the proton and neutron. Also note that the mass of the proton and neutron is close to 1 amu. This is a useful fact to remember. If the number of electrons does not equal the number of protons in the nucleus then the atom is an ion:
cation: number of electrons < number of protons
anion: number of electrons > number of protons
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