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Elizabeth Williams receives resources from the Australian research Council.

You are watching: How do isotopes of an element differ from one another



The regular table of elements. Cepheus/Wikimedia

Building block of matter

An atom is composed of an incredibly thick core (called a nucleus) that protons and also neutrons, surrounded by a diffuse cloud that electrons.

You have the right to think that protons and also neutrons as the exact same kind of fragment with one crucial difference: the protons space positively charged, when neutrons bring no charge. This way protons can “feel” electrical or magnetic fields, while neutrons cannot.

The electrons, i beg your pardon are lot lighter 보다 protons or neutrons, bring the same magnitude of fee as a proton yet with the contrary sign, an interpretation that each atom that has equal number of protons and electrons is electrically neutral.

It is the electron that identify the chemical behaviour of a details element.


The Map the Nuclides consists of information about all recognized isotopes. The limits of this map space constantly spreading, as new research help us uncover ways to make brand-new isotopes. Elements are assigned a heat on the chart according come the variety of protons lock have. Steady isotopes are displayed in black. National Nuclear Data facility / Wikimedia Commons

Isotopes that an facet share the same number of protons yet have different numbers the neutrons. Let’s use carbon together an example.

There are three isotope of carbon discovered in nature – carbon-12, carbon-13, and also carbon-14. Every three have actually six protons, but their neutron number - 6, 7, and also 8, respectively - all differ. This means that all 3 isotopes have different atomic masses (carbon-14 gift the heaviest), yet share the very same atomic number (Z=6).

Chemically, all three are indistinguishable, due to the fact that the number of electrons in every of these 3 isotopes is the same.

So different isotopes that the same facet are identical, chemically speaking. Yet some isotopes have actually the ability to circumvent this rule by transforming into another element entirely.


3 naturally occurring carbon isotopes. While each have the same variety of protons and also electrons, they different in the variety of neutrons. Tessa Koumoundouros

Marching towards stability

This transformative capacity some isotope have needs to do with the reality not every isotopes are stable, and also is what led Frederick Soddy to his Nobel Prize-winning discovery of isotopes in 1913.

Some isotopes - such together carbon-12 - will certainly happily continue to exist as carbon unless something particularly happens. Rather - carbon-14, to speak - will at some point decay into a secure isotope nearby.

In this case, among the neutron in carbon-14 changes into a proton, developing nitrogen-14. During this process, i m sorry is known as beta decay, the nucleus emits radiation in the kind of one electron and an antineutrino.


A carbon-14 ghost turns into a proton throughout beta decay. Tessa Koumoundouros

There are many factors the can reason a nucleus come decay. One of the most important is the proportion of protons to neutrons a particular nucleus has. If a nucleus has actually too countless neutrons (the definition of “too many” counts on how heavy the cell core is), over there is a possibility that that will degeneration towards stability.

The same is true if a nucleus has actually too plenty of protons. This is among the factors why some isotopes of a given aspect are radioactive, while others are not.

From the bellies of stars

By now, you might be wondering just how all these isotopes were produced in the first place. Together it transforms out, this concern is a facility one, yet lends some fact to the adage the we are all made of star dust.

Some that the lighter isotope were formed very early in the history of the universe, throughout the large Bang. Others result from procedures that happen within stars or together a an outcome of chance collisions in between highly energetic nuclei - recognized as cosmic rays - in ~ our atmosphere.

Most normally existing isotopes are the final (stable or long-lived) product result from a long series of atom reactions and also decays.

In most of this cases, light nuclei have had to smash in addition to enough energy to enable the solid force - a glue-like shortcut that develops when protons and also neutrons obtain close sufficient to touch - to get over the electromagnetic force – i beg your pardon pushes proton apart. If the solid force wins out, the colliding nuclei tie together, or fuse, to kind a more heavier nucleus.

Our sunlight is a great example that this. Among its main sources of power is a collection of combination reactions and beta degeneration processes the transform hydrogen into helium.


Isotopes degeneration towards what is sometimes referred to as the “valley of stability.” Araghu/Wikimedia

Transforming knowledge right into tools

Since the early 1900s, when the existence of isotopes was very first realised, atom physicists and also chemists have actually been seeking out ways to study how isotopes have the right to be formed, exactly how they decay, and how we might use them.

As it turns out, the nature of isotope – their chemical uniformity, their nuclear distinctiveness – provides them beneficial for a wide selection of applications in areas as diverse as medicine, archaeology, agriculture, strength generation and also mining.

If friend have ever before had a pets scan, you have actually benefited from a byproduct the the radioactive degeneration of details isotopes (often called medical isotopes). We create these clinical isotopes using our knowledge of how nuclear reaction proceed, v the help of nuclear reactors or accelerators dubbed cyclotrons.

But we have additionally found methods to make use of naturally emerging radioactive isotopes. Carbon dating, for example, provides use that the long-lived isotope carbon-14 come determine how old objects are.

Under typical circumstances, carbon-14 is produced in our setting via cosmic beam reactions v nitrogen-14. It has actually a half-life of about 5,700 years, which way that fifty percent of a quantity of carbon-14 will have actually decayed away in the time period.

within the Australian nationwide University’s 15 Million Volt accelerator. ANU

While a biological organism is alive, the takes in approximately one carbon-14 isotope for every trillion stable carbon-12 isotopes and also the carbon-12 come carbon-14 ratio stays about the exact same while the organism lives. Once it dies, new intake that carbon stops.

This way the proportion of carbon-14 to carbon-12 changes in the stays of this organism end time.

If us extract carbon using chemical techniques from a sample, we deserve to then apply a technique called accelerator fixed spectrometry (AMS) to separate out the individual carbon isotope by weight.

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AMS renders use of the reality that accelerated particles with the exact same charge however different masses monitor separate courses through magnetic fields. Through making use of these different paths, we can determine isotope ratios v incredible accuracy.

As you deserve to see from these examples, we apply our knowledge of isotopes in a range of ways. We produce them, finding them, extract them, and also study them with the double purpose of knowledge why the atomic nucleus behaves as it does, and also how we can harness its strength for ours benefit.