In fact, the periodic table is arranged in order of increasing atomic number. A second number is needed to fully describe an atom. This number is called the mass number. Since the mass of an atom ...

The Atomic Mass Data Center and its electronic bulletin are tools for the exchange of information on experimental masses, evaluation of masses, extrapolation of masses, and theoretical masses. One of ...

equivalent to the positive charge of the atom) was less than the atomic mass (average mass of the atom). For example, a helium atom has an atomic mass of 4, but an atomic number (or positive ...

Photo: Niels Bohr's research notes for his new atomic theory ... Rutherford deduced that the atom must have nearly all its mass, and positive charge, in a central nucleus about 10,000 times ...

Another frontier pursued by cutting edge research here is the crafting of atom-light interactions so precise that a new generation of atomic clocks can be envisioned, whose accuracy approaches 1 ...