Atomic number, atomic mass, and isotopes (article) | Khan Academy
The number of electrons in a neutral atom is equal to the number of protons. The only difference between these isotopes is the number of neutrons in the. Atoms and isotopes are identified by the numbers of protons, neutrons and What is the relationship between the number of protons and the number of. An atom is a nucleus with bound electrons, and an isotope is a way to distinguish between different types of nuclei. The main difference is the weight and so some physical and chemical properties depending only on weight are effected.
The relative atomic masses given in periodic table entries—like the one for hydrogen, below—are calculated for all the naturally occurring isotopes of each element, weighted by the abundance of those isotopes on earth.
What is the difference between an atom and isotope?
Extraterrestrial objects, like asteroids or meteors, might have very different isotope abundances. Isotopes and radioactive decay As mentioned above, isotopes are different forms of an element that have the same number of protons but different numbers of neutrons. Many elements—such as carbon, potassium, and uranium—have multiple naturally occurring isotopes. A neutral atom of Carbon contains six protons, six neutrons, and six electrons; therefore, it has a mass number of 12 six protons plus six neutrons.
Neutral carbon contains six protons, eight neutrons, and six electrons; its mass number is 14 six protons plus eight neutrons. These two alternate forms of carbon are isotopes.
Structure of the Atom
Some isotopes are stable, but others can emit, or kick out, subatomic particles to reach a more stable, lower-energy, configuration. Such isotopes are called radioisotopes, and the process in which they release particles and energy is known as decay. Radioactive decay can cause a change in the number of protons in the nucleus; when this happens, the identity of the atom changes e.
The ratio of the original isotope to its decay product and to stable isotopes changes in a predictable way; this predictability allows the relative abundance of the isotope to be used as a clock that measures the time from the incorporation of the isotope e. For example, carbon is normally present in the atmosphere in the form of gases like carbon dioxide, and it exists in three isotopic forms: As plants pull carbon dioxide from the air to make sugars, the relative amount of carbon in their tissues will be equal to the concentration of carbon in the atmosphere.
As animals eat the plants, or eat other animals that ate plants, the concentrations of carbon in their bodies will also match the atmospheric concentration.
After a half-life of approximately 5, years, half of the carbon that was initially present will have been converted to nitrogen This property can be used to date formerly living objects such as old bones or wood. By comparing the ratio of carbon to carbon concentrations in an object to the same ratio in the atmosphere, equivalent to the starting concentration for the object, the fraction of the isotope that has not yet decayed can be determined.
On the basis of this fraction, the age of the material can be calculated with accuracy if it is not much older than about 50, years.
Other elements have isotopes with different half lives, and can thus be used to measure age on different timescales. The atomic nucleus is made up of electrically positive protons and electrically neutral neutrons. Surrounding the atomic nucleus are the electrically negative electrons.
- Atomic number, atomic mass, and isotopes
The masses and charges of these three fundamental constituents of atoms are given below: This number of protons is called the atomic number. The mass of the atom, its atomic mass, depends upon both the number of protons and upon the number of neutrons present in the nucleus remember that the mass of an electron is so small that it is simply ignored for the purpose of establishing the atomic mass. Before moving further into this unit, link to: This is not easy.
For many of the chemical elements there are several known isotopes. Isotopes are atoms with different atomic masses which have the same atomic number. The atoms of different isotopes are atoms of the same chemical element; they differ in the number of neutrons in the nucleus.Atomic number, mass number, and isotopes - Chemistry - Khan Academy
Most elements as they occur naturally on earth are mixtures of several isotopes. For example, the element hydrogen has atoms that have one proton in the nucleus.
This is the most common form of hydrogen. Most of the atoms of hydrogen found in the Universe are 1H. Occasionally, one finds and atom of hydrogen in which a neutron has been incorporated into the nucleus. This isotope of hydrogen is characterized by an atomic number of one only one proton; hydrogen can only have one proton in the nucleusbut an atomic mass of two one proton plus one neutron. This isotope of hydrogen is known as "deuterium" or heavy hydrogen. Finally, even rarer is the third isotope of hydrogen [3H].
It has a mass of three which can only occur from the presence of two neutrons in the nucleus. Remember, that if there was another proton in hydrogenit would not be hydrogen.
This final isotope of hydrogen is known as "tritium" and it is radioactive. Later, we shall consider isotopes again when we consider the important question of atomic mass Moles of Atoms Historical background. The atomic mass of an element is a relative quantity. Originally the atomic mass of hydrogen, the lightest of the elements, was taken to be one and the atomic masses of all other elements were measured in relation to the atomic mass of hydrogen.
This later proved to have been a poor choice. Not only does hydrogen naturally consist of more than one isotope, but there was the additional question particularly among early chemists as to whether monatomic hydrogen or diatomic hydrogen should be taken as having atomic mass one.