a)define the atomic mass unit.
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Answer:
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Explanation:
An atomic mass (symbol: ma) is the mass of a single atom of a chemical element. It includes the masses of the 3 subatomic particles that make up an atom: protons, neutrons and electrons. ... 1 atomic mass unit is defined as 1/12 of the mass of a single carbon-12 atom.
Answer:
Explanation:
➯Masses of individual atoms are very, very small. Using a modern device called a mass spectrometer, it is possible to measure such minuscule masses. An atom of oxygen-16, for example, has a mass of 2.66 × 10 -23 g. While comparisons of masses measured in grams would have some usefulness, it is far more practical to have a system that will allow us to more easily compare relative atomic masses. Scientists decided on using the carbon-12 nuclide as the reference standard by which all other masses would be compared. By definition, one atom of carbon-12 is assigned a mass of 12 atomic mass units (amu). An atomic mass unit is defined as a mass equal to one twelfth the mass of an atom of carbon-12. The mass of any isotope of any element is expressed in relation to the carbon-12 standard. For example, one atom of helium-4 has a mass of 4.0026 amu. An atom of sulfur-32 has a mass of 31.972 amu.
➯The carbon-12 atom has six protons and six neutrons in its nucleus for a mass number of 12. Since the nucleus accounts for nearly all of the mass of the atom, a single proton or single neutron has a mass of approximately 1 amu. However, as seen by the helium and sulfur examples, the masses of individual atoms are not whole numbers. This is because an atom’s mass is affected very slightly by the interactions of the various particles within the nucleus, and the small mass of the electron is taken into account.
⇒Carbon-12 is the reference for all atomic mass calculations.
⇒An atomic mass unit is defined as a mass equal to one twelfth the mass of an atom of carbon-12.
⇒The mass of an atom is affected by the interactions of particles within the nucleus.