Atomic mass molecular masses by comparing the vapor density of a collection of gases with molecules containing one or more of the chemical element in question. In the 20th century, until the 1960s chemists and physicists used two different atomic-mass scales. The chemists used a "atomic mass unit" (amu) scale such that the natural mixture of oxygen isotopes had an atomic mass 16, while the physicists assigned the same number 16 to only the atomic mass of the most common oxygen isotope (O, containing eight protons and eight neutrons). However, because oxygen-17 and oxygen-18 are also present in natural oxygen this led
Given name a name is not assigned at birth, one may be given at a naming ceremony, with family and friends in attendance. In most jurisdictions, a child's name at birth is a matter of public record, inscribed on a birth certificate, or its equivalent. In western cultures, people normally retain the same given name throughout their lives. However, in some cases these names may be changed by following legal processes or by repute. People may also change their names when immigrating from one country to another with different naming conventions. In certain jurisdictions, a government-appointed registrar of births may refuse to