Studying the composition of matter, scientists came to the conclusion that all matter consists of molecules and atoms. For a long time, the atom (translated from Greek as "indivisible") was considered the smallest structural unit of matter. However, further studies have shown that the atom has a complex structure and, in turn, includes smaller particles.
What is an atom made of?
In 1911, the scientist Rutherford suggested that the atom has a central part that has a positive charge. This is how the concept of the atomic nucleus first appeared.
According to Rutherford's scheme, called the planetary model, an atom consists of a nucleus and elementary particles with a negative charge - electrons moving around the nucleus, just as the planets orbit around the Sun.
In 1932, another scientist, Chadwick, discovered the neutron, a particle that has no electric charge.
According to modern concepts, the structure of the atomic nucleus corresponds to the planetary model proposed by Rutherford. The nucleus is carried inmost of the atomic mass. It also has a positive charge. The atomic nucleus contains protons - positively charged particles and neutrons - particles that do not carry a charge. Protons and neutrons are called nucleons. Negatively charged particles - electrons - orbit around the nucleus.
The number of protons in the nucleus is equal to the number of electrons moving in orbit. Therefore, the atom itself is a particle that does not carry a charge. If an atom captures other people's electrons or loses its own, then it becomes positive or negative and is called an ion.
Electrons, protons and neutrons are collectively referred to as subatomic particles.
The charge of the atomic nucleus
The nucleus has a charge number Z. It is determined by the number of protons that make up the atomic nucleus. Finding out this amount is simple: just refer to the periodic system of Mendeleev. The atomic number of the element to which an atom belongs is equal to the number of protons in the nucleus. Thus, if the chemical element oxygen corresponds to the serial number 8, then the number of protons will also be equal to eight. Since the number of protons and electrons in an atom is the same, there will also be eight electrons.
The number of neutrons is called the isotopic number and is denoted by the letter N. Their number may vary in an atom of the same chemical element.
The sum of protons and electrons in the nucleus is called the mass number of an atom and is denoted by the letter A. Thus, the formula for calculating the mass number looks like this: A=Z+N.
Isotopes
When elements have an equal number of protons and electrons, but a different number of neutrons, they are called isotopes of a chemical element. There can be one or more isotopes. They are placed in the same cell of the periodic system.
Isotopes are of great importance in chemistry and physics. For example, an isotope of hydrogen - deuterium - in combination with oxygen gives a completely new substance, which is called heavy water. It has a different boiling and freezing point than usual. And the combination of deuterium with another isotope of hydrogen - tritium leads to a thermonuclear fusion reaction and can be used to generate a huge amount of energy.
Mass of the nucleus and subatomic particles
The sizes and masses of atoms and subatomic particles are negligible in human concepts. The size of the kernels is approximately 10-12cm. The mass of an atomic nucleus is measured in physics in the so-called atomic mass units - amu
For one amu take one twelfth of the mass of a carbon atom. Using the usual units of measurement (kilograms and grams), the mass can be expressed as follows: 1 a.m.u.=1, 660540 10-24g. Expressed in this way, it is called the absolute atomic mass.
Despite the fact that the atomic nucleus is the most massive component of the atom, its dimensions relative to the electron cloud surrounding it are extremely small.
Nuclear Forces
Atomic nuclei are extremely stable. This means that protons and neutrons are held in the nucleus by some forces. Is notthere may be electromagnetic forces, since protons are like-charged particles, and it is known that particles with the same charge repel each other. The gravitational forces are too weak to hold the nucleons together. Therefore, particles are held in the nucleus by a different interaction - nuclear forces.
Nuclear interaction is considered the strongest of all existing in nature. Therefore, this type of interaction between the elements of the atomic nucleus is called strong. It is present in many elementary particles, as well as electromagnetic forces.
Features of nuclear forces
- Short action. Nuclear forces, unlike electromagnetic forces, manifest themselves only at very small distances comparable to the size of the nucleus.
- Charge independence. This feature is manifested in the fact that nuclear forces act equally on protons and neutrons.
- Saturation. The nucleons of the nucleus interact only with a certain number of other nucleons.
Core Binding Energy
Another thing is closely connected with the concept of strong interaction - the binding energy of nuclei. Nuclear binding energy is the amount of energy required to split an atomic nucleus into its constituent nucleons. It is equal to the energy required to form a nucleus from individual particles.
To calculate the binding energy of a nucleus, it is necessary to know the mass of subatomic particles. Calculations show that the mass of a nucleus is always less than the sum of its constituent nucleons. The mass defect is the difference betweenthe mass of the nucleus and the sum of its protons and electrons. Using the Einstein formula about the relationship between mass and energy (E=mc2), you can calculate the energy generated during the formation of the nucleus.
The strength of the binding energy of the nucleus can be judged by the following example: the formation of several grams of helium produces as much energy as the combustion of several tons of coal.
Nuclear reactions
The nuclei of atoms can interact with the nuclei of other atoms. Such interactions are called nuclear reactions. There are two types of reactions.
- Fission reactions. They occur when heavier nuclei break down into lighter ones as a result of the interaction.
- Reactions of synthesis. The process is the reverse of fission: the nuclei collide, thereby forming heavier elements.
All nuclear reactions are accompanied by the release of energy, which is subsequently used in industry, in the military, in energy and so on.
Familiarizing with the composition of the atomic nucleus, we can draw the following conclusions.
- Atom consists of a nucleus containing protons and neutrons, and electrons around it.
- The mass number of an atom is equal to the sum of the nucleons of its nucleus.
- Nuclons are held together by the strong force.
- The huge forces that give the atomic nucleus stability are called the binding energies of the nucleus.
