Atoms that have the same atomic number but different atomic masses are called isotopes. The difference in mass arises due to the atoms containing a different number of neutrons for the same number of protons.Continue Reading
The identity of an element is determined by the number of protons each of its nuclei contains. Protons are positively charged and held together in a small space. The electrostatic force of repulsion between the like charges is very high, but they are able to remain stable due to the presence of neutrons. Neutrons are neutral subatomic particles found within the nucleus of an atom. The protons and neutrons are the heaviest subatomic particles and constitute the entire atomic mass of an element.
When two atoms have the same number of protons, they are said to be from the same element. However, if they differ in atomic mass, it means that the number of neutrons in the nuclei is different for the two atoms. Since the number of neutrons does not change the electron configuration of the atoms, the two atoms have the same chemical properties. However, they have different physical properties, such as boiling point, melting point and density, because their atomic masses are different.
To account for the similarities in chemical properties but the difference in physical properties, the two atoms of the same element are called isotopes of that element. For example, hydrogen has two other isotopes, deuterium and tritium, caused by the addition of extra neutrons in the nucleus without a change in the number of protons or electrons.Learn more about Atoms & Molecules
The number next to isotopes signifies the sum of the number of protons plus the number of neutrons in the nucleus of an atom. For a particular element, the number of protons never changes, but the number of neutrons can vary.Full Answer >
All isotopes of the same element share a common number of protons and electrons, though they vary in their relative numbers of neutrons. All isotopes of a given element are chemically identical, and they form bonds with other elements in the same way regardless of their neutron count or intrinsic stability.Full Answer >
The atomic mass is not given as a whole number because it is a weighted average taken of all of an atom's isotopes found in nature relative to the mass of carbon-12. The measurement unit used for atomic mass is the unified atomic mass that has the symbol "u." This is a derived unit from the carbon-12 isotope, where 12 u is the atomic mass of carbon-12.Full Answer >
All isotopes of a given element must share the same atomic number, which equals the number of protons. An isotope is denoted by its atomic number in the lower left-hand corner next to its chemical symbol and its mass number in the upper left next to the symbol.Full Answer >