Do at home (or in a school circle) such an experience. Take an electric battery and connect it with wires to a light bulb from a flashlight. Current will flow through the bulb, it will light up. Then cut one wire and dip its ends into a glass of water. The light bulb will not light, which means there is no current. Now pour ordinary salt into a glass. When the salt dissolves, the bulb will light up again. So, as soon as the water turned into a salt solution, a current went through it. And why?
You have probably already heard (and if not, read the story "" in this book) that in an atom they revolve around the nucleus. And why do they stay in the atom and don't fly away?
Take a stone and spin it on a rope above your head. You feel that the stone is always trying to fly away, and the rope is holding it.
And the atom has its own "rope". These are electrical charges. The nucleus of an atom is positively charged, the electrons are negatively charged. Such dissimilar charges, as they are called, attract each other. This attraction keeps the electrons near the nucleus.
But if you strongly unwind the stone on a thin rope, it will come off and fly away. And the electron can come off. For example, with a sharp collision of atoms. It's like a bunch of grapes: shake it and the berry will fall.
But what will happen to the atom itself? When the electron is torn off, the atom becomes positively charged.
The departed electron can meet another atom on the way and "stick" to it. Then this atom will become negatively charged.
These charged atoms are called ions.
Not only individual atoms, but also groups of atoms can lose or gain electrons. At the same time, they also turn into ions, and the transformation itself is called ionization.
If the gas is heated strongly, its atoms will move with great speed and many electrons will be torn off during collisions. The gas will become ionized.
Various substances are ionized by the action of radioactive radiation. And at a height of hundreds of kilometers above the Earth, ions arise under the action of special rays from the Sun. This layer of the atmosphere is called the ionosphere.
Many solids are also made up of ions. For example, salt. When it dissolves in water, the ions move apart. As soon as these charged particles appeared in the water, they began to transfer electricity from one end of the wire to the other, and the solution began to pass an electric current.
The movement of ions is the basis for the operation of many devices and devices created by man, for example, or an electric battery. And in nature, ions play an important role. There are many different ions moving in every cell of your body. You go skiing or write a dictation - these are the ions at work. And now you are reading our book, and ions are moving in your brain cells. If not for them, you would not be able to think, could not study, read, would not know what ions are.
A particle that contains a different number of protons and electrons is called an ion. If the number of protons is greater, the ion acquires a positive charge and becomes a cation. Ions with a negative charge (electrons predominate) are called anions.
general description
For the first time in chemistry, the concept of "ion" appeared in 1834 thanks to the experiments of Michael Faraday. The scientist studied the electrical conductivity of aqueous solutions of acids, salts, alkalis. He suggested that the ability to conduct electricity is due to the movement of charged particles - ions in a solution.
Molecules are capable of disintegrating into ions - atoms with a lack or excess of an electron. The decomposition process is called electrolytic dissociation, and the resulting solution or melt is called electrolyte. If the electrode is lowered into the electrolyte solution, the cations will begin to move towards the cathode - the negative pole, the anions - towards the anode - the positive pole. This explains the electrical conductivity of electrolytes.
Rice. 1. Movement of ions under the action of an electrode.
In solutions or melts, ions are formed under the action of water molecules or high temperature.
Structure
Ions are made up of a nucleus and electrons moving around. The nucleus is formed by positively charged particles (protons) and neutral particles (neutrons). The number of protons is the same as the atomic number of the element. The number of neutrons is equal to the value of the difference between the relative atomic mass and the number of protons.
Electrons are located on energy levels. The number of levels matches the period the element is in. The outer energy level contains valence electrons that can interact with other atoms. When an atom loses valence electrons, it becomes a cation; when an additional electron is added, it becomes an anion.
For example, if one more electron is attached to a chlorine atom, it becomes a negatively charged ion - an anion. And if one electron is taken away from the sodium atom, it will become a positively charged ion - a cation, because. there will be more protons than negative electrons.
Cations in the equations are marked with a plus, and anions with a minus. For example, Fe 2+ , Al 3+ , Na + , F - , Cl - . The number means how many electrons the atom gave or received, becoming an ion, i.e. shows the degree of oxidation. The number of cations or anions can be viewed from the table of the solubility of substances.
Rice. 2. Table of solubility.
Classification
Ions are divided into two groups:
- simple or monoatomic - contain one core, i.e. consist of one atom of matter;
- complex or polyatomic - contain at least two cores, i.e. composed of two or more atoms of matter.
Simple ions include cations and anions of metals and non-metals - Na +, Mg 2+, Cl -. Complex ions are formed when an ion is attached to neutral molecules of a substance. For example:
- NH 3 + H + → NH 4 +;
- BF 3 + F - → BF 4 - .
Cations are ions of metals, hydrogen, ammonium and some other substances. Anions are hydroxide ion (OH -), ions of acidic residues, non-metals and other substances.
Some atoms can become cations or anions depending on the reaction.
Radical ions are also isolated - free charged particles capable of attaching atoms or joining atoms of other substances. Depending on the charge, they are divided into radical cations and radical anions.
Ionic bond - a class of connection of ions. An ionic bond arises as a result of the electrostatic attraction of anions and cations. An atom with a higher electronegativity attracts an atom with a lower electronegativity. Ionic bonding occurs predominantly between metal and non-metal ions. Metal always donates electrons, i.e. is a restorer.
Rice. 3. Diagram of the ionic bond.
What have we learned?
From the topic of the lesson, we learned what ions are. An atom becomes an ion by removing or gaining electrons. If there are fewer electrons, then the atom acquires a positive charge due to the predominance of protons and becomes a cation. With an increase in the number of negatively charged electrons, the atom becomes an anion. Ions are capable of transmitting electricity and are necessarily present in electrolytes. An ionic bond arises between ions due to the electrostatic attraction of negative and positively charged particles.
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And he is an electrically charged particle. In this case, the ion can have both a positive electric charge and a negative one. In the first case, it is called a cation, and in the second, an anion.
An ion can be an atom, a molecule, or a free radical, as long as they have any charge, of course. By the way, the charge of an ion cannot be infinitely small, and the particle by which it is represented is elementary.
Ions are also chemically active particles, so they can react both with other particles (not charged) and with each other.
Ions, as independent particles, are found almost everywhere. They are in the atmosphere, in various liquids, in solids, and even in interstellar space, where there is, in principle, extremely little air or some kind of substance.
Story
For the first time the concept of "ion" was introduced by the famous scientist Michael Faraday in 1834. Studying the propagation of electricity in various media, he suggested that the electrical conductivity of some of them may be caused by the presence of certain electrically charged particles in these media and substances. So he called them ions. The scientist also introduced the concepts of cations and anions. Since the positive ions move towards the negatively charged electrode, the cathode, he called them cations. Negative ions move the other way around - towards the anode, which means they should be called anions.
Almost everyone has seen an advertisement for the so-called "Chizhevsky chandelier", from which negative ions in the air increase quantitatively. However, after school, not everyone remembers exactly the Ions themselves - these are charged particles that have lost their neutrality characteristic of normal atoms. And now a little more.
"Wrong" atoms
As you know, the number in the periodic table of the great Mendeleev is associated with the number of protons in the nucleus of an atom. Why not electrons? Because the number and completeness of electrons, although it affects the properties of an atom, does not determine its fundamental properties associated with the nucleus. There may not be enough electrons, or there may be too many. Ions are just atoms with the "wrong" number of electrons. Moreover, paradoxically, those with a lack of electrons are called positive, and an excess is called negative.
A little about names
How are ions formed? This is a simple question - there are only two ways of education. Either chemical or physical. The result can be a positive ion, which is often called a cation, and a negative one, respectively, an anion. A single atom or a whole molecule, which is also considered to be an ion of a special polyatomic type, can have a deficiency or an excess of charge.
If there is an ionization of a medium, for example, a gas, then there are quantitatively proportional ratios of electrons and positive ions in it. But such a phenomenon is rare (during a thunderstorm, near a flame), the gas in such an altered state does not exist for long. Therefore, in general, reactive air ions close to the ground are rare. Gas is a very rapidly changing medium. As soon as the action of ionizing factors ceases, the ions meet each other and again become neutral atoms. This is their normal state.
Aggressive liquid
Ions in large quantities can be contained in water. The fact is that water molecules are particles in which they are distributed unevenly over the molecule, they are dipoles that have a positive charge on one side and a negative charge on the other.
And when a soluble substance appears in water, water molecules with their poles electrically affect the added substance, ionizing it. A good example is seawater, where many substances exist in the form of ions. This has been known to people for a long time. There are a lot of ions in the atmosphere above a certain point, this shell is called the ionosphere. destroys stable atoms and molecules. Particles in an ionized state can impart to the whole substance. An example is the bright unusual colors of gems.
Ions are the basis of life, because the basic process of obtaining energy from ATP is impossible without the creation of electrically unstable particles, itself based on the interactions of ions and many chemical processes catalyzed by enzymes, occurs only due to ionization. It is not surprising that some substances in this state are taken by mouth. A classic example is useful silver ions.