Protons and neutrons make up the nucleus of an atom while electrons revolve around the nucleus in constant motion.
How big is an atom?
The core occupies a total space of 10-15 m. Considering the orbits of the electrons, the atom occupies a lot of space at a distance of about 10-11 meters.
Therefore, the atom consists largely of free space. Characteristics of Subatomic Particles Quarks Characteristics of Subatomic Particles Protons and neutrons are called nucleons. They make up about 99.9% of the total mass of the atom. Nucleons (protons and neutrons) are linked by the strong nuclear force or strong interaction.
This is a much stronger force than the electromagnetic force, but with a more limited range of action. The electrons around the atom are attracted to the positive charge of the atomic nucleus. A weaker force but with greater range.
Subatomic particles have different characteristics. Protons have a positive electric charge (+ 1.6 10–19 C). Neutrons have no electric charge. Electrons have a negative charge opposite to protons (-1.6 10-19 C). Protons and neutrons have the same mass. The mass of the neutron is slightly higher (1,675 10-27 kg) than the proton (1,672 10-27 kg).
In fact, protons and neutrons are not true elementary particles, as they are instead made up of smaller subatomic particles called quarks. A quark is a subatomic particle with a fractional electric charge. Two types of quarks make up neutrons and protons. Up quark has an electric charge of +2/3 quarks down, its electric charge is -1/3, a proton is made up of two up quarks and one down quark. Therefore, the proton has a positive electric charge equal to +1.
A neutron is made up of two down quarks and one up quark. Therefore, the neutron has zero electric charge.
Quarks are the oldest particles. They first appeared at the birth of the universe during the Big Bang, about 14 billion years ago. Moments before the formation of protons and neutrons. And so on.
Atoms are the building blocks of matter. They consist of the atomic nucleus and the nuclear shell. The atomic nucleus is composed of positively charged particles, protons and uncharged neutrons, which in turn are composed of other elementary particles. The negatively charged electrons are located around the core, that is, in the shell.
While the atomic nucleus makes up the main mass of the atom, the nuclear shell determines its shape and chemical properties.
The precise structure of the nuclear shell is very complex and can be described in a simplified manner using Bohr’s shell model. It is believed that the electrons of the atomic shell move around the nucleus in circular paths, shells.
Since this model is only valid to a limited extent, the so-called orbital model is used today to describe the atomic shell. An orbital is a mathematical function that describes the behavior of an electron. Graphically, the probability of an electron being present in space can take various forms, e.g. Spherical (S orbital) and dumbbell-shaped (P orbital).
The energy states of electrons in the electron shell are given by the electron configuration.
Carbon Atom: Orbital Model
The orbital model of carbon. Spherical s orbitals are shown in blue, dumbbell-shaped p orbitals in green. The electron configuration of carbon is 1s2 2s2 2px1 2py1. There are 2 electrons on the s orbital with the principal quantum number 1 (=K shell). So one speaks of 1s orbital and writes 1s2. 2 electrons are assigned to the s orbital with principal quantum number 2 (=l shell), described as 2s2, and one electron each on the px and py orbitals, as well as principal quantum number 2 (= L-) bark). The 4 electrons with the principal quantum number 2, that is, the outermost ones, are called outer electrons (simplified shown as red dots).
Atoms are the basic building blocks of all matter. The word atom is derived from the Greek word atomos, which means “indivisible”. Chemically, atoms are virtually indivisible; They make up the smallest unit of every chemical element. A hydrogen atom, for example, is the smallest unit of the element hydrogen (element symbol: H).
Today we know that atoms are physically divisible. They are made up of smaller particles; so-called elementary particles. These make up the nuclear shell and the atomic nucleus. The atomic nucleus consists of positively charged protons and electrically neutral neutrons. There are negatively charged electrons in the atomic shell. In an atom, the number of electrons in the shell always matches the number of protons in the nucleus.
The charge carried by charged elementary particles (i.e. electrons and protons) is called elementary charge () and is given in coulombs (C).
The negatively charged electrons have a charge of -1.6 10–19 C, the positively charged protons have a charge of +1.6 10–19 C. In terms of quantity, protons and electrons have the same charge.
normal and mass number
Since an atom is completely uncharged, the number of protons in the atomic nucleus and electrons in the atomic shell must be the same. This is the only way to balance their charges. The number of protons in the nucleus of an atom is called the atomic number. All atoms of the same element have the same number of protons and therefore have the same atomic number. It is usually given in subscript to the left of the element symbol.
Protons and neutrons are about 2000 times heavier than electrons. Hence the atomic nucleus forms the main mass of the atom. The total number of protons and neutrons is called the mass number (also called the nucleon number). This roughly corresponds to the mass of the atom and can be found in superscript to the left of the element symbol. The mass of electrons is so small that it is neglected here.
An atom which is given atomic number and mass number is called a nuclide. For example, there is a nuclide of oxygen. Nuclides have more than two neutrons.
Relative atomic mass
The atomic mass unit (u) is used for the mass of atoms. It is defined as 1/12 of the mass of an atom of carbon nuclide and is:
1 u = 1.66057 x 10-27 kg
The relative atomic mass (M) of the atom is therefore 12 u. One always speaks of “relative” atomic masses when referring to atomic masses, since the information relates to a relative size (1/12 of the mass of the atom).
The atomic shell is where electrons reside and hence it is also known as electron shell. The electron shell is about 20,000 to 150,000 times larger than the atomic nucleus, but it is only about 1/2000 of the atomic mass due to the small mass of the electrons.
The spatial region of residence is described by the square of the magnitude of the wave function, the so-called orbital. The wave function consists of discrete numbers called quantum numbers. These provide information about the shell on which the electron is located (principal quantum number), the spatial distribution of the probability of being located (secondary quantum number) as well as the spatial orientation (magnetic quantum number) and orbital angular momentum (spin). ) quantum number of electrons.
Strictly speaking, the formulation that electrons are in an orbital is incorrect, they are described by the orbital.
If the orbitals described by the wave function are represented graphically, they can assume different shapes: the s orbital is spherical, for example, the p orbitals are dumbbell-shaped.
Orbitals, the regions where electrons reside in the atomic shell, have different sizes. For example, s-orbitals are circular, p-orbitals are dumbbell shaped.
Even though the orbital model is not based on the fact that electrons move on clearly defined paths around the atomic nucleus, principle quantum numbers are often assigned the concept of shells, which is known from earlier models. The distance from the atomic nucleus, i.e. the shell where the electron is located, depends on the energy content of the electron. Electrons are attracted to the positively charged atomic nucleus – so the lower-energy electrons are closer to the atomic nucleus than the more energetic ones.
Simply put, the principal quantum numbers of orbitals correspond to different shells of the electron shell. The energy of electrons described by these prime quantum numbers increases with increasing distance from the atomic nucleus.
Principal Quantum Number (n)
To describe in which shell (i.e. at which energy level) an electron is located, it is given a numerical value, the so-called principal quantum number (1, 2, 3, …, n). The electrons with the lowest energy level having a numerical value of 1, are located on the innermost shell, called the K shell. The more energetic the electrons which are in the second shell, the L shell gets the original quantum number 2 etc.
Small Quantum Number (L)
The secondary quantum number (0, 1, 2, …, n – 1) indicates the type of orbital on which the electron is located. If the secondary quantum number of an electron is 0, it is located on a circular s orbital, 1 for the dumbbell-shaped p orbital, 2 for the a d orbital and 3 for the f orbital.
Magnetic Quantum Number (M)
With the help of the magnetic quantum number, it is possible to find out which and above all, how many orbitals can be found in which shells. The magnetic quantum number can assume values between +l (l = secondary quantum number) and –l. As a reminder: l = 0 = s orbital, l = 1 = p orbital, etc.
For the k shell (n = 1), l = 0 (s orbital), since l can take all values up to n–1. Therefore the magnetic quantum number (m) can also only take the value 0. This means that there is exactly one s orbital on the first shell.
The L-shell can take the values 0 (s-orbital) and 1 (p-orbital) with (n = 2). If l = 0 then m is also 0. The second shell also has an s orbital. For L = 1, however, M = -1, 0 and +1. The fact that m can assume three different values means that there are 3 p orbitals in addition to one orbital on the l orbital. The 3 p orbitals are called px, py and pz.
With the m-shell (n = 3) the l can take values 0, 1 and 2 (d-orbital). So we know that the m-shell consists of one s-orbital (m=0) and 3 p-orbitals (m=-1, 0 and +1). For l = 2, m can take five different values, namely −2, −1, 0, +1 and +2. Besides the s and p orbitals, there are five other d orbitals.
Spin Quantum Number(s)
The last important quantum number is the spin quantum number. It can take the values + and –. The spin quantum numbers of electrons in an orbital should not be the same. Therefore, a maximum of 2 electrons can be present on each orbital (be it s, p or d orbital).
Electron configuration indicates in which energy state (shell) and in which lounge (orbit) the electrons of an atom are located. When distributing electrons into shells and orbitals, one must keep in mind that the states with the lowest energy are always given priority. Two electrons cannot agree in all four quantum numbers (Pauli principle) and if the orbitals are energetically similar (for example three p orbitals), they must be filled with one electron first before filling with another electron (Hundt’s rule). are given.
A similar notation is used for electron configuration. First the shell on which the electron is located is named, then the orbital and then the number of electrons in the orbital. Here’s an example:
Boron has serial number 5 and hence 5 electrons. The electron configuration of an atom is according to the above rules:
1s2, 2s2, 2p1
The first shell (K shell) is completely occupied with 2 electrons on the s orbital. The second shell (L shell) can accommodate 1 s and 3 p orbitals for a total of 8 electrons. In the case of borrowing, it is not fully occupied. In this case, there are 2 electrons in the s and one electron in the p orbital in the second shell. The s-orbital of the second shell is energetically more favorable and therefore completely occupied with 2 electrons, with the 5th electron occupying only one of the p-orbitals.
The L-shell is the outermost shell of boron. The outer shell is also known as the valence shell. Their electrons are called valence electrons (outer electrons). Therefore boron has 3 valence electrons.
Atoms try to adopt an energetically favorable state. This is achieved when the outermost shell’s orbitals are completely filled with electrons. The elements in the first period of the PSE (hydrogen and helium) have only one shell, the K shell, with an s orbital on it. It is completely occupied with 2 electrons. Therefore the atoms of the first period tend to have 2 valence electrons.
The octet rule applies to atoms of elements from the second period of the PSE. It says that atoms try to achieve an outer shell completely surrounded by 8 electrons. The energetically favorable electron configuration is called the noble gas configuration.
But why is the outer shell completely filled with exactly 8 electrons? Quite simply: on the outermost shell of elements from the second period, one s and three p orbitals are usually the outermost orbitals. There is space for exactly 8 electrons on these 4 orbitals. The absolute occupation of orbitals is particularly favorable in terms of energy and so is its purpose.
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