by Ron Kurtus (revised 15 September 2015)
An element is defined as an atom with a specific number of protons in its nucleus, determining its atomic number and chemical characteristics. There are usually several possible number of neutrons for the specific element. Each element typically has several isotopes, as determined by the number of neutrons in its nucleus.
Typically, one amount of neutrons is most stable for an element and is the most abundant atom in the element. Special characteristics of the rare or unstable isotopes allow for applications of them.
Questions you may have include:
- How many neutrons are in a nucleus?
- What are some examples of isotopes?
- How are isotopes used?
This lesson will answer those questions.
Each element has isotopes
An element is defined as an atom with a specific number of protons in its nucleus, determining its atomic number.
Protons have a positive (+) electrical charge. The number of protons in a nucleus results in an equal number of electrons in orbits around the nucleus. Electrons have a negative (-) charge and determine the chemical characteristics of the atom.
Since the electrical charge of protons tend to push them apart, neutrons are included in the nucleus to help hold it together. There is no firm formula to determine how many neutrons are required in a nucleus, but it seems that one value results in a more stable atom than others.
The element will primarily consist of atoms with the most stable number of neutrons in their nuclei. But there will also be atoms of that element with other numbers of neutrons. Atoms with the various numbers of neutrons are called isotopes of the element. Although all combinations are isotopes, usually the most stable is called the element and the less common atoms are called the isotopes.
Examples of isotopes
Each element has at least several isotopes. Here are a few examples:
Carbon typically has 6 protons and 6 neutrons in its nucleus. Although it is not as common, there is an isotope of Carbon with 7 neutrons. It is called Carbon-13 and consists of 1% of all Carbon atoms. Another isotope is Carbon-14, which has 8 neutrons and is radioactive. Carbon-14 consists of less than one-billionth of Carbon in nature.
Oxygen has 8 protons in its nucleus. But its nucleus may contain 8, 9 or 10 neutrons and still be stable. There there other numbers of neutrons possible, but they are unstable and decay into something else within a fraction of a second. The atom with 8 protons and 8 neutrons is the most common and makes up 99% of all Oxygen.
Often the isotopes are written according to the total number of protons and neutrons in their nuclei (nuclei is plural of nucleus, from Latin). Thus, we would have Oxygen-16, O-17 and O-18.
Uses of isotopes
The less common isotopes of an element have a different atomic weight than the common form of the element. They may also be unstable and radioactive.
Hydrogen usually has a nucleus consisting of only one proton. An isotope of Hydrogen--called Deuterium--has a nucleus consisting of one proton and one neutron. When Deuterium combines with oxygen, it forms what is called "heavy water" because the Deuterium component of the water is twice as heavy as if it was simple hydrogen.
Although the amount of heavy water molecules in nature is very small (1 part in 3200), it has been concentrated for use in the development of nuclear weapons. Also, when concentrated, it can be poisonous to plants and animals.
Since the Carbon-14 (C-14) isotope is radioactive, the amount of it in an object that was once living can be used to approximate the date of death. While living, a plant or animal renews carbon in its system. Once the object dies, the amount of C-14 only changes as it decays into some other material. Since C-14 decays at a rate where half of it has changed in about 5600 years--known as its half-life--the years since death can be calculated.
Thus, if the object or fossil has only 1/4 of the C-14 in it as compared with living objects, it died around 11,200 years ago.
Of course, since C-14 normally consists of 1/1,000,000,000 of the carbon found in nature, the measurements can be difficult to make and certainly aren't exact.
An element is an atom with a specific number of protons in its nucleus and several possible numbers of neutrons. Each of these atoms is called an isotope of the element. Typically, one amount of neutrons is most stable for an element and is the most abundant atom in the element. Special characteristics of the rare or unstable isotopes allow for various applications.
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