As early as 1871, Dmitri Mendeleev, one of the two first developers of the periodic table of the elements, predicted the properties of chemical elements that were still unknown. It was based on the periodic table of the time. He inferred these unknown elements from gaps. By interpreting the physical and chemical properties of the neighbors of these unknown elements, he was able to deduce their properties.
Many of the properties predicted were consistent with the elements later discovered. As you can see, the periodic table of the elements is an important tool for every chemist, from which the relationships, structure, properties and other information about the chemical elements can be read.
General information about the periodic table of elements
In the periodic table of the elements, PSE for short, all 118 chemical elements are shown in tabular form. The name of the periodic table is based on the periodic, i.e. regularly, recurring properties of the elements. In addition to the natural elements of chemistry, the artificial chemical elements can also be found in the periodic table of the elements.
Artificial elements are chemical elements that do not exist naturally but have been artificially created by humans. These are the elements in the periodic table with atomic number 95 to 118. Natural elements are therefore chemical elements that occur naturally.
Element charts in the periodic table
The chemical elements are represented on the periodic table using element charts. The element cards contain the element symbol and the atomic number of the respective element. Additional information such as atomic mass, full name, electronegativity, density, physical state, radioactivity and occurrence of an element is often also given. It depends on the respective periodic table which information is actually displayed.
The properties of the elements are displayed differently. Properties are not only represented in writing, i.e. by digits or numerical values, but also, for example, by colored fonts, hatching, underscores or colored backgrounds. The affiliation of the elements to metals, semi-metals or non-metals is partly distinguished by background colors.
Atomic number of a chemical element
The atomic number indicates the number of protons in the nucleus of the element in question. With the help of this atomic number, the chemical elements are ordered in the periodic table, which is why the atomic number is also called the atomic number. You can usually find the atomic number in the upper left corner of the element card.
Element symbol of a chemical element
The element symbol consists of one or two letters and is derived from the Greek or Latin name of the element. Since the element names have been translated into German, an element’s element symbol does not always match its German name. One such example is hydrogen. The element symbol of hydrogen is not «W» or «Wa», but «H», which is derived from the Latin word hydrogenium can be deduced.
Atomic mass of a chemical element
The atomic mass indicates the weight of a single atom of the element in question. You can use the atomic mass to calculate the mass of a molecule. To do this, you multiply the atomic mass by the number of occurring atoms of the element and add up the results of the different elements. In the periodic table you can often find the atomic mass in the upper right corner or below the element symbol.
Physical state of a chemical element
The states of aggregation of the elements under normal conditions, i.e. at a temperature of 25° Celsius and a pressure of 1013 hPa, are sometimes also given in the periodic table. The physical state describes the physical state of a substance. A substance can be solid, liquid or gaseous.
Electronegativity of a chemical element
Electronegativity describes the tendency of an atom in a molecule to attract the electrons in the electron pair bond. The higher the value of an element’s electronegativity, the more strongly it attracts the electrons of the bond(s) towards itself.
Periodic table – structure
As you already know by now, the chemical elements in the PSE are ordered according to their atomic number. In addition, the elements are in so-called periods and groups sorted.
Periodic Table – Periods
The rows of the periodic table of the elements are periods called. The periodic table of the elements has a total of seven periods, most of which are numbered with Arabic numerals. The number of the respective period indicates the number of electron shells of the atom in the shell model.
The elements are arranged in such a way that the atomic number increases from left to right. So you can read the increasing atomic numbers of the elements of the periodic table from left to right like a book and then jump to the next line.
The shell model is based on Niels Bohr’s atomic model. You can think of an atom like an onion. The innermost part of the onion represents the nucleus, while the individual shells of the onion are the so-called electron shells. The electrons of an atom are arranged in these shells, although not every shell can hold the same number of electrons. The outermost electron shell of an atom is called the valence shell. The electrons in it are therefore also called valence electrons.
Representation of the periodic table
The periods of the periodic table do not all contain the same number of elements. Except for the first period, all other periods have eight main group elements. The first period, on the other hand, has only two main group elements (hydrogen (H) and helium (He)). If the subgroups of the periodic table are also included, the first period has two elements, the second and third periods each have eight elements, the fourth and fifth periods each have eighteen elements and the last two periods each have 32 elements.
Because it takes a lot of space to display 32 elements side by side, a medium-length shape is often used to represent the periodic table. Fourteen elements from the last two periods are «cut out» of the periodic table and displayed under the periodic table.
Periodic Table – Groups
The columns of the periodic table are called groups designated. The line breaks of the periods are selected in such a way that the groups of the periodic table contain chemical elements with similar properties or similar reaction behavior.
The groups are usually numbered with Roman numerals, whereby they are divided into so-called main and sub-groups. There are a total of eighteen groups in the periodic table.
Main groups in the periodic table of elements
Eight of the eighteen groups on the periodic table are major groups. The main group number indicates the number of valence electrons, i.e. the number of electrons in the outermost shell of the atom. Since elements of a main group have the same number of electrons in the outermost electron shell, they often react in a similar way. Because of this, some main groups have a characteristic name:
Subgroups in the periodic table of elements
All subgroup elements are metals and often form colored compounds. You are certainly familiar with some of these colored compounds, such as yellowish gold (Au) or reddish copper (Cu). The ten sub-groups are each named after the top element.
The numerical designation of the subgroups does not go from one to ten, but starts with three. It is simply counted on after the first two main groups, leaving out the tens in the eleventh and twelfth groups, i.e. the last two subgroups. As a result, these two groups are referred to as the first and second subgroups. In the table you can see the subgroups with their names and numerical designations:
Advantages of building the periodic table
You can rightly ask yourself why you don’t just list the properties of the elements in a big table. Why do you go to the trouble of dividing the elements into periods, main groups and subgroups? The question is quickly answered: With the help of the structure of the periodic table, you have a great overview, both of the respective main and subgroups, but also of the properties and the atomic structure of the chemical elements. This makes it easier for you to deduce the reaction behavior of the elements.
The periodic table is not just a pure classification system. Rather, it is an instrument for making predictions about chemical reactions and bonds, but also the basis for explaining chemical processes.
Trends in the periodic table
In addition to reading the properties of the individual elements, you can also see trends in the periodic table of the elements. This allows you to infer further properties or behavior of the respective elements.
atomic radius
The atomic radius of an atom increases the further you go down in the respective main group. You can derive this trend from the shell model. The higher the period of an element in the respective main group, the more electron shells this atom has. And the more electron shells an atom has, the larger the radius of the atom.
While the atomic radius increases from top to bottom in a main group, it decreases in a period from left to right. The reason for this is the number of protons in the atom. The further to the right an element is in a period, the higher the positive charge of the atomic nucleus because it contains more protons. The more positive nuclear charge pulls the negatively charged electrons more towards the nucleus, which reduces the atomic radius.
That is, helium has the smallest atomic radius since it is found in the first period and the eighth main group. Cesium, on the other hand, is the element of the non-radioactive, i.e. stable elements, which has the largest atomic radius. You can find cesium in the first main group and the sixth period.
Unstable elements are all those chemical elements whose atomic nucleus changes due to the emission of radiation. As a result of the change, the atom transforms into a different chemical element. You probably know the emitted radiation under the name «radioactive radiation». Stable atoms are atoms whose nucleus is stable.
ionization energy
The ionization energy is the energy that must be applied to release an electron from the valence shell, i.e. the outermost shell of the atom. The further to the right an element is in the respective period, the higher the ionization energy, since the number of protons in the atomic nucleus increases and the electrons are thus attracted more and more to the atomic nucleus. Consequently…