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Differences in the atoms of the same element

Atoms belonging to the same element have the same nucleus charge (identical number of protons) and the same number of electrons moving around the nucleus. However, as it turns out, these atoms can differ in mass. The reason for this phenomenon is the possibility that different numbers of neutrons occurs in the nucleus of atoms of the same element. Those atoms that have more neutral particles have a larger mass.

The atoms of the element with the same number of protons, and different number of neutrons in the nucleus are called isotopesisotopesisotopes.

The element with several isotopes is nitrogen. There are seven neutrons in the nucleus of one of them, and in the nucleus of the other – eight neutrons. Each of these isotopes has the same number of protons that can be found in the periodic table.

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Ilustracja przedstawia fragment układu okresowego. W przybliżeniu widać azot i jego liczbę atomową - siedem.

The information on the number of neutrons isotopes contain is important in their description. Therefore, mainly mass number providing information on the number of these particles is used in its description. The atomic number is usually omitted due to the fact that it can be found in the periodic table.

Isotopes are presented in two ways: the mass number is placed in the upper index on the left side of the symbol of the element or after the dash after the name of the element, e.g. ${}^{\text{14}}\text{N}$ or nitrogen‑14.

Isotopes of hydrogen in nature

Isotopes with the same atomic number belong to the same element. In principle, these show identical properties, with the only exception being hydrogen isotopes. The hydrogen in nature is a mixture of mainly two isotopes in stable‑state: ${}^{\text{1}}\text{H}$ (99.985%) and ${}^{\text{2}}\text{H}$ (0.015%). It means that of 100,000 atoms of hydrogen, 99,985 are isotopes ${}^{\text{1}}\text{H}$, and 15 atoms – isotopes ${}^{\text{2}}\text{H}$. There is also the third, unstable isotope ${}^{\text{3}}\text{H}$. It occurs in trace amounts. The isotopes of hydrogen were the only ones in the world of elements to have their names: protium, deuterium and tritium.

Symbol of hydrogen isotope
${}^{\text{1}}\text{H}$ or hydrogen‑1
Name of hydrogen isotope – protium

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Ilustracja przedstawia model atomu protu - czerwoną kulę z białą kulką pośrodku.

Symbol of hydrogen isotope
${}^{\text{2}}\text{H}$ or hydrogen‑2
Name of hydrogen isotope – deuterium

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Ilustracja przedstawia model atomu deuteru - czerwoną kulę z białą i niebieską kulą pośrodku.

Symbol of hydrogen isotope
${}^{\text{3}}\text{H}$ or hydrogen‑3
Name of hydrogen isotope – tritium

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Ilustracja przedstawia model atomu trytu - czerwoną kulę z białą i dwiema niebieskimi kulkami pośrodku.

It is easy to see that hydrogen isotopes differ in the number of nucleons. For this reason, there is a large mass difference between them, for example the deuterium atom has a mass twice as large as the weight of the protium and the tritium mass is three times larger than protium. This phenomenon affects the properties of these isotopes: protium, deuterium and tritium have different properties.

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Ilustracja przedstawia napis Isotopes of potassium.

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Nazwy trzech izotopów potasu: potas trzydzieści dziewięć, czterdzieści i czterdzieści jeden. Symbol chemiczny litera ka. W przypadku pierwszego izotopu: liczba masowa trzydzieści dziewięć, liczba atomowa dziewiętnaście. W przypadku drugiego izotopu odpowiednio czterdzieści i dziewiętnaście. W przypadku trzeciego izotopu - czterdzieści jeden i dziewiętnaście. Obliczenia liczby neutronów: od liczby masowej odejmujemy liczbę atomową. W przypadku pierwszego izotopu liczba neutronów wynosi dwadzieścia. U drugiego izotopu dwadzieścia jeden, u trzeciego dwadzieścia dwa.

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Napis: Isotopes: are variations of the same element that differ in the number of neutrons in the atomic nucleus. They have the same chemical properties and differ slightly in physical properties.

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Napis: Nucleon is a component of the atomic nucleus, i.e. a proton or a neutron. The number of neutrons is determined by the mass number of the chemical element.

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Napis: Proton nuclear constituents to a weight of about one and one unita and has a positive charge. The number of protons in the nucleus determines the atomic number Z. All atoms of the same element contain the same number of protons in the atomic nucleus.

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Napis: Neutron is a component of the atomic nucleus with a mass of about one unita and is electrically neutral. The number of neutrons in the nucleus is equal to the difference in mass number and atomic number. Individual atoms of a given element may have different numbers of neutrons.

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Napis: The mass number is the number of nucleons in the atomic nucleus of a given chemical element. This is the sum of protons and neutrons. It's an isotope feature, not an element. The mass number is not the mass of the atom, but the sum of the protons and neutrons.

Summary

• Isotopes are atoms of the same chemical element that have the same number of protons and different number of neutrons.

• Most of the chemical elements found in nature are a mixture of isotopes with a stable composition.

• Isotopes of hydrogen are: protium (${}^{\text{1}}\text{H}$), deuterium (${}^{\text{2}}\text{H}$) and tritium (${}^{\text{3}}\text{H}$). Their properties are different.

Keywords

isotope, atom, proton, neutron, protium, deuterium, tritium

Glossary