The single electron of a hydrogen atom forms around the nucleus spherical orbital- a spherical electron cloud, like a loosely wound ball of fluffy wool or a cotton ball.

Scientists have agreed to call the spherical atomic orbital s-orbital. It is the most stable and is located quite close to the core.

The greater the energy of an electron in an atom, the faster it rotates, the more its area of ​​residence stretches out and finally turns into a dumbbell-shaped p-orbital:

An electron cloud of this shape can occupy an atom three positions along the space coordinate axes x, y And z. This is easily explained: after all, all electrons are negatively charged, so electron clouds repel each other and strive to be located as far away from each other as possible.

Together, three electron clouds, which are called p x-, p y- or p z-orbitals, form a symmetrical geometric figure, in the center of which is the atomic nucleus. It looks like a six-pointed pompom or a triple bow - as you like.

So, p There can be three orbitals. Their energy, of course, is the same, but their location in space is different.

Except s- And p-orbitals, there are electronic orbitals of even more complex shapes; they are designated by letters d And f. The electrons that enter here acquire an even greater supply of energy, move along complex paths, and as a result, complex and beautiful three-dimensional geometric shapes are obtained.

All d-orbitals(and there may already be five of them) are identical in energy, but differently located in space. And in shape, reminiscent of a pillow tied with ribbons, only four are identical.
And the fifth is like a dumbbell threaded through a donut.

Electron clouds with the same energy, which are given a name f-orbitals, maybe already seven. They are also different in shape and differently oriented in space.

Electronic cloud- a visual model reflecting the distribution of the probability density function of detecting an electron in an atom or molecule depending on the energy of the electron.

The figure shows the radial distribution of the probability of finding an electron in a hydrogen atom in the ground state.

The radial distribution curve of the probability of finding an electron in a hydrogen atom shows that the probability of finding an electron is maximum in a thin spherical layer with a center at the proton location and a radius equal to the Bohr radius a 0 .

The stronger the connection between the electron and the nucleus, the smaller the electron cloud and the denser the charge distribution.

The electron cloud is most often depicted as a boundary surface (covering approximately 90% of the density). In this case, the density designation using dots is omitted.

Electron cloud and chemical bonding

Assuming the motion of electrons to be independent of the much slower nuclear motions (adiabatic approximation), it is possible to quite strictly describe the formation of a chemical bond as a result of the action of Coulomb forces of attraction between positively charged atomic nuclei to the electron cloud concentrated in the internuclear space (see Fig. 2).

The charge of this cloud tends to bring the nuclei closer to each other (bonding region), while the electronic charge outside the internuclear space (non-bonding region) tends to push the nuclei apart. Nuclear repulsion forces act in the same direction. When atoms approach each other at an equilibrium distance, part of the electron density from the non-bonding region passes into the bonding region. The electron charge is distributed in both regions so that the forces tending to bring the nuclei together and repel them are the same. This is achieved at a certain equilibrium distance corresponding

Previously, scientists believed that electrons orbited positively charged nuclei and were kept at a certain distance from them.

It has now been proven that such orbits do not exist in atoms. Based on calculations and experimental data, scientists have established that an electron, when moving, can be at different distances from the nucleus. I was also able to install probability of stay electrons at a certain distance from the nucleus.

The presence of an electron at a certain distance from the nucleus is conventionally represented by dots. Where the electron is more often, the arrangement of points is more dense, where it is less often, it is less dense.

When an electron moves, for example, in an H atom, it forms a kind of spherical cloud.

The set of different electron positions is considered as electron cloud with a certain negative charge density.

Near the nucleus, you can select a space where the probability of finding an electron is greatest.

The space around the atomic nucleus in which an electron is most likely to be found is called electron cloud.

S-electrons have a spherical shape of the electron cloud.

C - 1S 2 2 S 2 2P 2 P-electrons have a dumbbell-shaped electron shape. clouds

(regular figure eight shape).

The shape and size of a particular electron cloud are determined atomic orbitals. Atomic orbitals are a function of the dual nature of the electron, defined at each point in circumnuclear space. They have no form, because... This is a mathematical concept. However, like their corresponding electron clouds, orbitals are designated by the symbols s, p, d, f.

In atoms chemical elements The first layer corresponds to one s orbital, which can contain two s electrons. The second layer has an s-orbital, the energy reserve of the electrons in it is higher than that of the electrons of the first layer. In addition, the second layer has three p-orbitals, which correspond to dumbbell-shaped electron clouds of the same size. They are mutually perpendicular, like the x, y, and z coordinate axes. The third layer, in addition to one s- and three p-orbitals, has five d-orbitals.

There are 2 Sē in the He atom. Therefore, the question arises: how can two spherical electron clouds coexist at the same energy level?

It turns out that in addition to the movement around the nucleus, which we have already considered, electrons also have a movement that can be represented as their rotation around their own axis. This rotation is called spin(translated from English - spindle).

One orbital can contain only 2 ē having opposite (antiparallel) spins, i.e. one ē seems to rotate around an axis clockwise, and the other - counterclockwise.

As a result experimental research It was found that, for example, in natural oxygen In addition to oxygen atoms with mass 16, there are also atoms with mass 17 and 18.

Varieties of atoms of the same element that have the same nuclear charge (same number of protons in the nucleus) but different masses ( different number neutrons) are called isotopes.

Or a molecule depending on the energy of the electron.

The figure shows the radial distribution of the probability of finding an electron in a hydrogen atom in the ground state.

The radial distribution curve of the probability of finding an electron in a hydrogen atom shows that the probability of finding an electron is maximum in a thin spherical layer with a center at the proton location and a radius equal to the Bohr radius a 0 .

The stronger the connection between the electron and the nucleus, the smaller the electron cloud and the denser the charge distribution.

The electron cloud is most often depicted as a boundary surface (covering approximately 90% of the density). In this case, the density designation using dots is omitted.

Encyclopedic YouTube

1 / 3

What is an orbital

#8 Chemistry: Atomic structure

Electronic structure of the atom

Subtitles

Electron cloud and chemical bonding

Assuming the motion of electrons to be independent of much slower nuclear motions (adiabatic approximation), we can quite strictly describe the formation of a chemical bond as a result of the Coulomb forces of attraction of positively charged atomic nuclei to an electron cloud concentrated in the internuclear space (see Fig. 2).

The charge of this cloud tends to bring the nuclei closer to each other (bonding region), while the electronic charge outside the internuclear space (non-bonding region) tends to push the nuclei apart. Nuclear repulsion forces act in the same direction. When atoms approach an equilibrium distance, part of the electron density from the nonbonding region passes into the bonding region. The electron charge is distributed in both regions so that the forces tending to bring the nuclei together and repel them are the same. This is achieved at a certain equilibrium distance corresponding

Structure of electronic shells

According to quantum mechanical concepts, an electron, like any other microparticle, simultaneously has corpuscular and wave properties (particle-wave dualism), i.e. properties of particles and waves. To describe the state (motion) of an electron in an atom, a probabilistic approach is used, based on the concepts of the electron cloud, atomic orbital and electron density.

Electronic cloud – a model of the movement of an electron in an atom, which assumes that the negative charge of the electron is unevenly distributed throughout the entire volume of space around the nucleus (the electron is, as it were, “smeared” in this volume). When graphically depicting an electron cloud, this is shown by the unequal density of dots: where the dots are denser, the electron is located there more often.

The density of the electron cloud (electron density) decreases with distance from the nucleus.

In a multielectron atom, electrons are located in atomic orbitals (AO). Atomic orbital – this is the state of an electron with a certain energy value, shape and spatial orientation of the electron cloud.

Spherical orbitals are designated by the letter s, and the electrons occupying these orbitals are called s-electrons.

Orbitals in the form of a three-dimensional figure of eight (dumbbells) are designated by the letter p, and the electrons located on them are called p-electrons.

As it moves away from the nucleus, the energy of the electron increases (the strength of its bond with the nucleus decreases), and the size of the orbital in which the electron is located also increases. Accordingly, while maintaining the shape of the orbital and the number of electrons in it, the electron density decreases. When constructing electronic graphic circuits, an AO is depicted as a cell (quantum cell), and an electron is depicted as an arrow.

The electron is characterized spin, which can be simplified to represent the rotation of an electron around its own axis clockwise or counterclockwise. Depending on this, the electron is designated by arrows: or ↓.

If there is one electron on an AO, then it is called unpaired. The two electrons located on the joint-stock company are called paired or electron (lone) pairs.

There are no more than two electrons on one AO, and their spins must be in opposite directions.