The atomic mass is carried by the atomic nucleus, which occupies only about 10 -12В of the total volume of the atom or less, but it contains all the positive charge and at least 99.95% of the total mass of the atom. Since the density (ПЃ) of a substance is the total mass (m) of that substance divided by the total volume (V) occupied by that substance, it is obvious, the density of a substance strongly depends on its atomic mass and also on the atomic number densityВ (N atoms/cm 3), Density вЂ“ Atomic Mass and Atomic Number Density The Standard English unit is pounds mass per cubic footВ ( lbm/ft 3). The standard SI unit is kilograms per cubic meterВ ( kg/m 3). In words, the density (ПЃ) of a substance is the total mass (m) of that substance divided by the total volume (V) occupied by that substance. It is an intensive property, which is mathematically defined as mass divided by volume: Typical densities of various substances are at atmospheric pressure.ДensityВ is defined as the mass per unit volume. For example, the neutron number of uranium-238 is 238-92=146. We can determine the neutron number of certain isotope. Therefore, we cannot determine the neutron number of uranium, for example. Each nuclide is denoted by chemical symbol of the element (this specifies Z) with tha atomic mass number as supescript. The various species of atoms whose nuclei contain particular numbers of protons and neutrons are called nuclides. Nuclides that have the same neutron number but a different proton number are called isotones. Neutron number is rarely written explicitly in nuclide symbol notation, but appears as a subscript to the right of the element symbol. The difference between the neutron number and the atomic number is known as the neutron excess: D = N вЂ“ Z = A вЂ“ 2Z.

NeutronВ number plusВ atomic numberВ equals atomic mass number: N+Z=A. The total number of neutronsВ in the nucleus of an atom is called the neutronВ numberВ of the atom and is given the symbol N. Mass numbers of typical isotopes of GoldВ are 197. See also: Atomic Mass Number вЂ“ Does it conserve in a nuclear reaction? According to the Einstein relationship ( E=mc 2), this binding energy is proportional to this mass differenceВ and it is known as the mass defect. The difference is a measure of the nuclear binding energyВ which holds the nucleus together. Mass was no longer considered unchangeable in the closed system. Note that, it was found the rest mass of an atomic nucleusВ is measurably smaller than the sum of the rest masses of its constituentВ protons, neutronsВ and electrons. For 63CuВ the atomic mass is less than 63 so this must be the dominant factor. A nucleus with greater binding energy has a lower total energy, and therefore a lower massВ according toВ EinsteinвЂ™s mass-energy equivalenceВ relation EВ = mc 2.

The nuclear binding energyВ varies between nuclei.

This increases the mass of nuclei with more neutrons than protons relative to the atomic mass unit scale based on 12C with equal numbers of protons and neutrons.

The neutronВ isВ slightly heavierВ than the proton.

There are two reasons for the difference between mass number and isotopic mass, known as theВ mass defect: For example, 63CuВ (29 protons and 34 neutrons) has a mass number of 63 and an isotopic mass in its nuclear ground state is 62.91367 u. For other isotopes, the isotopic mass usually differs and is usually within 0.1 u of the mass number. One unified atomic mass unit is approximatelyВ the mass of one nucleon (either a single proton or neutron) and is numerically equivalent to 1 g/mol.ДЇor 12C the atomic mass is exactly 12u, since the atomic mass unit is defined from it. One atomic mass unit is equal to 1.66 x 10 -24В grams. The unit of measure for mass is the atomic mass unit (amu). Units of measure have been defined for mass and energy on the atomic scale to make measurements more convenient to express. The size and mass of atoms are so small that the use of normal measuring units, while possible, is often inconvenient. Note that, each elementВ may contain more isotopes, therefore this resulting atomic mass is calculated from naturally-occuring isotopes and their abundance. The atomic mass or relative isotopic mass refers to the mass of a single particle, and therefore is tied to a certain specific isotope of an element.

Periodic table with molar mass