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Learning Objectives

define what isotope are and how an isotope affect an element"s atomic mass. Identify the variety of protons, electrons, and neutrons that an facet with a offered mass number.

You are watching: How do two isotopes of the same element differ?

All atoms of the same aspect have the same variety of protons, but some may have various numbers the neutrons. Because that example, every carbon atoms have six protons, and also most have six neutrons as well. But some carbon atoms have actually seven or eight neutrons instead of the normal six. Atoms of the same aspect that different in their numbers of neutrons are referred to as isotopes. Countless isotopes happen naturally. Typically one or 2 isotopes that an element are the most stable and also common. Different isotopes that an element generally have actually the very same physical and also cg-tower.comical properties because they have actually the very same numbers of protons and electrons.

An Example: Hydrogen Isotopes

Hydrogen is an instance of an facet that has actually isotopes. Three isotopes of hydrogen room modeled in figure (PageIndex1). Many hydrogen atoms have actually just one proton, one electron, and lack a neutron. These atoms space just referred to as hydrogen. Some hydrogen atoms have actually one neutron together well. This atoms room the isotope named deuterium. Various other hydrogen atoms have actually two neutrons. These atoms are the isotope named tritium.

Figure (PageIndex1): The three many stable isotope of hydrogen: protium (A = 1), deuterium (A = 2), and also tritium (A = 3). (CC SA-BY 3.0; Balajijagadesh).

For most elements other 보다 hydrogen, isotopes are called for your mass number. For example, carbon atoms v the usual 6 neutrons have a mass number of 12 (6 proton + 6 neutron = 12), therefore they are called carbon-12. Carbon atoms with 7 neutrons have actually an atom mass that 13 (6 proton + 7 neutron = 13). These atoms space the isotope dubbed carbon-13.

Stability of Isotopes

Atoms require a specific ratio of neutrons to protons to have actually a stable nucleus. Having too many or too few neutrons family member to protons outcomes in one unstable, or radioactive, nucleus that will sooner or later malfunction to a more stable form. This procedure is dubbed radioactive decay. Plenty of isotopes have radioactive nuclei, and also these isotope are referred to as radioisotopes. Once they decay, they release particles that might be harmful. This is why radiation isotopes are dangerous and also why working v them requires special suits because that protection. The isotope the carbon recognized as carbon-14 is an instance of a radioisotope. In contrast, the carbon isotopes called carbon-12 and also carbon-13 are stable.

This whole discussion of isotopes brings us earlier to Dalton"s atom Theory. Follow to Dalton, atoms of a given facet are identical. Yet if atom of a given aspect can have different numbers the neutrons, then they deserve to have different masses as well! just how did Dalton miss this? It turns out that elements found in nature exist as consistent uniform mixture of their naturally occurring isotopes. In other words, a piece of lithium constantly contains both varieties of naturally arising lithium (the type with 3 neutrons and also the type with 4 neutrons). Moreover, it always contains the two in the very same relative quantities (or "relative abundance"). In a chunk of lithium, (93\%) will always be lithium v 4 neutrons, while the remaining (7\%) will always be lithium v 3 neutrons.

Dalton constantly experimented with huge chunks of an element—chunks that contained all of the naturally developing isotopes of that element. Together a result, when he carry out his measurements, he was actually observing the averaged properties of all the various isotopes in the sample. For many of our functions in cg-tower.comistry, us will perform the exact same thing and deal with the median mass that the atoms. Luckily, as well as having various masses, most other nature of various isotopes are similar.

There space two key ways in i beg your pardon scientists commonly show the mass number of an atom they space interested in. That is essential to keep in mind that the mass number is not provided on the periodic table. These two ways include writing a atom symbol or by giving the surname of the aspect with the massive number written.

To compose a nuclear symbol, the massive number is inserted at the top left (superscript) of the cg-tower.comical symbol and the atomic number is inserted at the lower left (subscript) the the symbol. The complete nuclear symbol for helium-4 is drawn below:


The complying with nuclear symbols space for a nickel nucleus through 31 neutrons and a uranium nucleus through 146 neutrons.

< ce ^238_92U>

In the nickel nucleus stood for above, the atom number 28 shows that the nucleus contains 28 protons, and therefore, it need to contain 31 neutron in stimulate to have actually a mass number of 59. The uranium nucleus has actually 92 protons, as all uranium nuclei do; and this specific uranium nucleus has actually 146 neutrons.

See more: What Is The Least Common Multiple Of 7 And 8 ? Least Common Multiple Of 7 And 8

Another means of representing isotopes is by including a hyphen and the massive number come the cg-tower.comical name or symbol. For this reason the two nuclei would certainly be Nickel-59 or Ni-59 and Uranium-238 or U-238, where 59 and 238 room the mass numbers of the two atoms, respectively. Note that the mass number (not the number of neutrons) are provided to the side of the name.


Exercise (PageIndex3)

How countless protons, electrons, and neutrons room in each atom?

(^60_27ceCo) Na-24 (^45_20ceCa) Sr-90 Answer a: 27 protons, 27 electrons, 33 neutrons Answer b: 11 protons, 11 electrons, 13 neutrons Answer c: 20 protons, 20 electrons, 25 neutron Answer d: 38 protons, 38 electrons, 52 neutrons