The periodic table
The modern periodic table organizes the known elements in several ways: it lists them in order of atomic weight patterns, electronic configuration, reactivity, and electronegativity.
It is such a good method of organizing and presenting known elements that it has been used to successfully predict the existence of certain elements.
Today, it is applied not only by chemists but also in all related sciences to understand the properties and reactivity of atoms and molecules.
Elements such as gold, silver, tin, copper, lead, and mercury are known since ancient times, the first scientific discovery of an element took place in 1649.
When Hennig Brand discovered phosphorus. Over the next 200 years, a vast body of knowledge concerning the properties of the elements and their compounds was acquired by chemists.
By 1869, a total of 63 elements had been discovered. As the number of known elements increased, scientists began to recognize patterns in properties and develop classification schemes.
Origins of the Periodic Table
The table has recognizable origins in the 17th century and is based on the knowledge and experience of medieval and earlier times.
Chemists have always looked for ways to organize elements to reflect similarities between their properties. The modern periodic table lists the elements in order to increase the atomic number (the number of protons in the nucleus of an atom).
Historically, however, the relative atomic masses were used by scientists trying to organize the elements.
However, the basis of the modern periodic table was well established and was even used to predict the properties of undiscovered elements long before the concept of atomic number was developed.
History of the Periodic Table
Atomic theory dates back to the ancient Greek philosophers and those of Hellenistic Egypt. They theorized that all substances were made of fundamental building blocks; however, the nature of those blocks was the subject of fierce debate.
The fundamental blocks were called atoms, derived from the Greek “atmos”, which means “indivisible”.
Early atomic theory attempted to explain the properties of matter by assigning attributes to atoms that could match the attributes of matter they combined to form, such as slipperiness, liquidity, color, and cohesion.
Philosophers categorized the world around them by property and function, a type of approach that later led to the development of the periodic table of elements.
The Middle Ages
In the Middle Ages, alchemists sought to make gold and lead-silver. Although his efforts were in vain, his research has finally led to a systematic understanding of the chemical world. It also established the mentality that gave us the periodic table of elements.
The alchemists were influenced by international trade, especially along the Silk Road between China and Europe.
Chemical knowledge spread across cultures, and by the mid-18th century, there were 33 known elements.
In the early 19th century, Joseph Proust and others were experimentally demonstrating the Definitive Proportions Act.
This provided fundamental evidence that matter existed in pure compounds rather than only in mixtures of any proportion.
These observations reinforced atomic theory and demanded a systematic method of organizing the elements.
First attempts to design a periodic table
If a periodic table is considered to be an order of chemical elements demonstrating the periodicity of chemical and physical properties, credit for the first periodic table (published in 1862) should probably be given to a French geologist, A.E.Beguyer de Chancourtois.
De Chancourtois transcribed a list of the elements positioned in a cylinder in terms of atomic weight gain.
When the cylinder was constructed so that 16 units of mass could be written into the cylinder per turn, the closely related elements were aligned vertically.
This led De Chancourtois to propose that “the properties of the elements are the properties of numbers”.
De Chancourtois was the first to recognize that elementary properties are repeated every seven elements, and using this table, he was able to predict the stoichiometry of various metallic oxides.
Unfortunately, his chart included some ions and compounds as well as elements.
Ask most of the chemists who discovered the periodic table and you will almost certainly get the answer from Dmitri Mendeleev. Certainly, Mendeleev was the first to publish a version of the table that we would recognize today, but does he deserve all the credit?
Several other chemists before Mendeleev were investigating patterns in the properties of the elements known at the time.
The first attempt to classify the elements was in 1789 when Antoine Lavoisier grouped the elements according to their properties into gases, non-metals, metals, and earth.
Other attempts were made to group elements in the coming decades. In 1829, Johann Döbereiner recognized triads of elements with chemically similar properties.
Like lithium, sodium, and potassium, and demonstrated that the properties of the medium element could be predicted from the properties of the other two.
It was not until a more accurate list of the atomic mass of the elements was available at a conference in Karlsruhe, Germany in 1860 that real progress was made toward the discovery of the modern periodic table.
The Modern of the Periodic Table
Scientists began to notice similarities and patterns among the known elements, and a great interest of 19th-century research was to develop a systematic method for reporting and classifying them.
Russian chemistry professor Dmitri Mendeleev and German chemist Julius Meyer independently presented their own versions of the periodic table in 1869 and 1870.
Mendeleev’s approach was finally adopted for several reasons: On the one hand, it left gaps for elements that had not yet been discovered.
In doing so, he predicted the elements gallium and germanium. He also placed the atoms based mainly on their chemical properties, not on the atomic mass.
It turns out that organization by chemical family correctly classifies most elements by their atomic number; atomic mass is not perfectly correlated with the atomic number.
The modern version of Mendeleev’s periodic table now contains some 118 different elements.
In the periodic table, the number above the symbol of the element is the atomic number, which represents the number of protons in the nucleus. The atomic mass is given by the sum of neutrons and protons.
Early philosophers and scientists appreciated that matter was composed of atoms and that many elements reacted in predictable proportions to each other. The periodic table was constructed to organize these observations and measurements.
The principle of valence arose, attributable to the presence or absence of electrons and to the energy of those electrons in the volume around the nucleus of an atom.
Electrons negatively charged subatomic particles, define the chemical reactivity of an atom. Electrons are organized in energy levels or layers of electrons, which correspond to the periods of the periodic table.
Who’s the father of the periodic table?
There has been some disagreement about who deserves the credit of being the “father” of the periodic table, the German Lothar Meyer or the Russian Dmitri Mendeleev.
Both chemists produced remarkably similar results while working independently of each other.
Meyer’s 1864 textbook included a fairly abridged version of a periodic table used to classify the elements.
This consisted of approximately half of the known elements listed in order of their atomic weight and demonstrated periodic changes of valence as a function of atomic weight.
In 1868, Meyer built an extended table which he handed over to a colleague for evaluation. Unfortunately for Meyer, Mendeleev’s desk was made available to the scientific community through publication (1869) before Meyer’s appearance (1870).
Who was Mendeleev?
Dmitri Ivanovich Mendeleev (1834-1907), the youngest of 17 children, was born in the Siberian town of Tobol’sk, where his father was a professor of Russian literature and philosophy.
Mendeleev was not considered an outstanding student in his early education, in part because of his aversion to classical languages, which were an important educational requirement at the time. Even though he showed proficiency in math and science.
After his father’s death, he and his mother moved to St. Petersburg to study at the university.
He finally got a place at the Main Pedagogical Institute (St. Petersburg Institute). Upon graduation, Mendeleev held the position of a science teacher in a gymnasium.
After some time as a professor, he was admitted to work as a graduate at the University of St. Petersburg, where he obtained a Master’s degree in 1856.
Classification of elements
In 1864, J.A.R. Newlands proposed classifying the elements in the order of increasing atomic weights.
Assigning to the elements ordinal numbers from the unit up and dividing them into seven groups that had properties closely related to the first seven of the elements then known: hydrogen, lithium, beryllium, boron, carbon, nitrogen and oxygen.
This relationship was called the law of octaves, by analogy with the seven intervals of the musical scale.
Then, in 1869, as a result of an extensive correlation of the properties and atomic weights of the elements.
With special attention to valence (i.e., the number of simple links that the element can form), Mendeleyev proposed the periodic law. Whereby “the elements ordered according to the magnitude of the atomic weights show a periodic change of properties”.
Lothar Meyer had independently arrived at a similar conclusion, published after the appearance of Mendeleyev’s article.
While writing a textbook on systematic inorganic chemistry, Principles of Chemistry, which appeared in thirteen editions, the last in 1947, Mendeleev organized his material in terms of families of known elements showing similar properties.
The first part of the text was devoted to the known chemistry of halogens. Then, he chose to cover the chemistry of the metallic elements in order to combine the power — first the alkaline metals (combining the power of one), the alkaline earth (two), etc.
However, it was difficult to classify metals such as copper and mercury, which had multiple combining powers, sometimes one and sometimes two.
While attempting to resolve this dilemma, Mendeleev noticed patterns in the atomic properties and weights of halogens, alkaline metals, and alkaline metals.
It noted similarities between the Cl-K-Ca , Br-/Rb-Sr and I-Cs-Ba series. In an effort to extend this pattern to other elements, he created a chart for each of the 63 known elements.
Each card contained the symbol of the element, its atomic weight, and its characteristic chemical and physical properties.
The periodic table of elements contains all the chemical elements that have been discovered or realized.
They are arranged, in the order of their atomic numbers, in seven horizontal periods, with the lanthanoids (lanthanum, 57, al lutetium, 71) and the actinoids (actinium, 89, al lawrencium, 103) indicated separately below. The periods are of variable duration.
Then there are two periods of eight elements each: the first short period, from lithium, 3, to neon, 10; and the second short period, from sodium, 11, to argon, 18.
Two periods of 18 elements each follow the first long period, from potassium 19 to Krypton, 36; and the second long period, from rubidium, 37 to xenon, 54.
The first very long period of 32 elements. From caesium, 55, to radon, 86, is condensed into 18 columns by the omission of the lanthanoids.
This allows the remaining 18 elements, which are very similar in their properties to the corresponding elements of the first and second long periods, to be placed directly below these elements.
The second very long period, from francio, 87, to oganesson, 118, is also condensed into 18 columns by the omission of the actinoides.
Classification of elements in groups
The six noble gases – helium, neon, argon, krypton, xenon, and radon – occur at the end of the six complete periods and constitute group 18 (0) of the periodic system.
It is common to refer to horizontal series of elements in the table as periods and vertical series as groups.
The seven elements lithium to fluorine and the seven elements corresponding to sodium to chlorine are placed, in Figure 1, in the seven groups, 1 (Ia), 2 (IIa), 13 (IIIa), 14 (IVa), 15 (Va), 16 (VIa), and 17 (VIIa), respectively.
The 17 elements of the fourth period, from potassium, 19, to bromine, 35, are distinct in their properties and are considered to constitute Groups 1-17 (Ia-VIIa) of the periodic system.
Periodic property trends
The periodicity in the properties of the elements arranged in order of atomic number is notably shown by the consideration of the physical state of the elemental substances and related properties such as melting point, density, and hardness. The elements of Group 18 (0) are difficult gases to condense.
Alkaline metals in Group 1 (Ia) are soft metal solids with low melting points. Alkali earth metals in Group 2 (IIa) are harder and have higher melting points than adjacent alkali metals.
Hardness and melting point continue to increase through Groups 13 (IIIa) and 14 (IVa) and then decrease through Groups 15 (Va), 16 (VIa) and 17 (VIIa).
Long-term elements show a gradual increase in hardness and melting point from the beginning of alkali metals to near the center of the period and then in Group 16 (VIb), an irregular decrease in halogens and noble gases.
How to read the Periodic table
In the periodic table there is an enormous amount of important information:
Atomic number: The number of protons in an atom is called the atomic number of that element.
The number of protons defines which element it is and also determines the chemical behavior of the element. For example, carbon atoms have six protons, hydrogen atoms have one, and oxygen atoms have eight.
Atomic symbol. The atomic symbol (or symbol of the element) is an abbreviation chosen to represent an element (“C” for carbon, “H” for hydrogen and “O” for oxygen, etc.).
These symbols are used internationally and are sometimes unexpected. For example, the tungsten symbol is “W” because another name for that element is Wolfram.
Also, the atomic symbol for gold if “Au” because the word for gold in Latin is aurum.
Atomic weight. The standard atomic weight of an element is the average mass of the element in atomic mass units (AMU).
Individual atoms always have an integer of atomic mass units. However, the atomic mass in the periodic table is indicated as a decimal number because it is an average of the various isotopes of an element.
The average number of neutrons of an element is obtained by subtracting the number of protons (atomic number) from the atomic mass.
Atomic weight for elements 93-118. For natural elements, the atomic weight is calculated from the average of the weights of the natural abundances of the isotopes of that element.
However, for laboratory-created transuranic elements – elements with atomic numbers greater than 92 – there is no “natural” abundance.
The convention is to list the atomic weight of the longest isotope in the periodic table. These atomic weights should be considered provisional, as a new isotope with a longer half-life could be produced in the future.
Super Heavy Elements
Within this category are super heavy elements or those with atomic numbers above 104.
The larger the nucleus of the atom. Which increases with the number of protons in its interior – the more unstable that element is, in general.
As such, these large elements are fleeting, lasting only milliseconds before decomposing into lighter elements, according to the International Union of Pure and Applied Chemistry (IUPAC).
For example, the super-weighted elements 113, 115, 117 and 118 were verified by IUPAC in December 2015. Completing the seventh row, or period, of the table.
Several different laboratories produced the super-heavy elements. The atomic numbers, temporary names and official names are:
- 113: ununtrium (Uut), nihonium (Nh)
- 115: ununpentium (Uup), moscovium (Mc)
- 117: ununseptium (Uus), tennessine (Ts)
- 118: ununoctium (Uuo), oganesson (Og)
Discovery of noble gases
In 1895 Lord Rayleigh reported the discovery of a new gaseous element called argon that turned out to be chemically inert.
This element did not fit into any of the known newspaper groups. In 1898, William Ramsey suggested that argon be placed on the periodic table between chlorine and potassium in a family with helium, even though the atomic weight of argon was greater than that of potassium.
This group was called the “zero” group because of the zero valence of the elements. Ramsey accurately predicted the future discovery and properties of neon.
The Modern Periodic Table
The last major changes in the periodic table were the result of Glenn Seaborg’s work in the mid-twentieth century.
From his discovery of plutonium in 1940, he discovered all the transuranic elements from 94 to 102. He reconfigured the periodic table by placing the actinide series underneath the lanthanide series.
In 1951, Seaborg received the Nobel Prize in Chemistry for his work. Element 106 has been named seaborgium (Sg) in his honor.
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