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The ancient Greeks thought that there were just four elements - earth, air, fire and water. However, we now know that there are actually 118 chemical elements. Everything on Earth and in the solar ...
- The Periodic Table - BBC Bitesize
If you know what one of the elements in a group is like, you...
- What are elements in science? KS3 guide for chemistry ... - BBC
Mercury is the only metal that is. liquid. at room...
- The Periodic Table - BBC Bitesize
If you know what one of the elements in a group is like, you can make predictions about the other elements in a group. For example, all the elements in group 1 are reactive metals, and all the ...
Mercury is the only metal that is. liquid. at room temperature. Some elements are non-metals. Most non-metals are. gases. gas One of the three states of matter. Gases, like oxygen or helium, do ...
- Overview
- History of the periodic law
- Classification of the elements
The periodic table is a tabular array of the chemical elements organized by atomic number, from the element with the lowest atomic number, hydrogen, to the element with the highest atomic number, oganesson. The atomic number of an element is the number of protons in the nucleus of an atom of that element. Hydrogen has 1 proton, and oganesson has 118.
What do periodic table groups have in common?
The groups of the periodic table are displayed as vertical columns numbered from 1 to 18. The elements in a group have very similar chemical properties, which arise from the number of valence electrons present—that is, the number of electrons in the outermost shell of an atom.
Where does the periodic table come from?
The arrangement of the elements in the periodic table comes from the electronic configuration of the elements. Because of the Pauli exclusion principle, no more than two electrons can fill the same orbital. The first row of the periodic table consists of just two elements, hydrogen and helium. As atoms have more electrons, they have more orbits available to fill, and thus the rows contain more elements farther down in the table.
Why does the periodic table split?
The early years of the 19th century witnessed a rapid development in analytical chemistry—the art of distinguishing different chemical substances—and the consequent building up of a vast body of knowledge of the chemical and physical properties of both elements and compounds. This rapid expansion of chemical knowledge soon necessitated classification, for on the classification of chemical knowledge are based not only the systematized literature of chemistry but also the laboratory arts by which chemistry is passed on as a living science from one generation of chemists to another. Relationships were discerned more readily among the compounds than among the elements; it thus occurred that the classification of elements lagged many years behind that of compounds. In fact, no general agreement had been reached among chemists as to the classification of elements for nearly half a century after the systems of classification of compounds had become established in general use.
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J.W. Döbereiner in 1817 showed that the combining weight, meaning atomic weight, of strontium lies midway between those of calcium and barium, and some years later he showed that other such “triads” exist (chlorine, bromine, and iodine [halogens] and lithium, sodium, and potassium [alkali metals]). J.-B.-A. Dumas, L. Gmelin, E. Lenssen, Max von Pettenkofer, and J.P. Cooke expanded Döbereiner’s suggestions between 1827 and 1858 by showing that similar relationships extended further than the triads of elements, fluorine being added to the halogens and magnesium to the alkaline-earth metals, while oxygen, sulfur, selenium, and tellurium were classed as one family and nitrogen, phosphorus, arsenic, antimony, and bismuth as another family of elements.
Attempts were later made to show that the atomic weights of the elements could be expressed by an arithmetic function, and in 1862 A.-E.-B. de Chancourtois proposed a classification of the elements based on the new values of atomic weights given by Stanislao Cannizzaro’s system of 1858. De Chancourtois plotted the atomic weights on the surface of a cylinder with a circumference of 16 units, corresponding to the approximate atomic weight of oxygen. The resulting helical curve brought closely related elements onto corresponding points above or below one another on the cylinder, and he suggested in consequence that “the properties of the elements are the properties of numbers,” a remarkable prediction in the light of modern knowledge.
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In 1864, J.A.R. Newlands proposed classifying the elements in the order of increasing atomic weights, the elements being assigned ordinal numbers from unity upward and divided into seven groups having properties closely related to the first seven of the elements then known: hydrogen, lithium, beryllium, boron, carbon, nitrogen, and oxygen. This relationship was termed 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 the atomic weights of the elements, with special attention to valency (that is, the number of single bonds the element can form), Mendeleyev proposed the periodic law, by which “the elements arranged according to the magnitude of atomic weights show a periodic change of properties.” Lothar Meyer had independently reached a similar conclusion, published after the appearance of Mendeleyev’s paper.
- Atoms. Atoms are the building blocks of matter. An atom has three basic parts – protons, neutrons and electrons. There are smaller particles, but they don’t concern us here.
- Atomic number. The atomic number of an element is the number of protons an atom has – the number of protons determines what an element is. For example, if an atom has six protons, it can only be carbon.
- Elements. An element is a substance that consists of atoms with the same atomic number. Elements cannot be split into simpler substances using normal chemical methods.
- The periodic table. It will help to have a copy of the periodic table – the one here will get you started, or you can print a full one from the website below.
Periodic table. The periodic table, also known as the periodic table of the elements, is an ordered arrangement of the chemical elements into rows ("periods") and columns ("groups"). It is an icon of chemistry and is widely used in physics and other sciences. It is a depiction of the periodic law, which states that when the elements are ...
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Periodic Table of Chemical Elements. The periodic table of chemical elements, often called the periodic table, organizes all discovered chemical elements in rows (called periods) and columns (called groups) according to increasing atomic number. Scientists use the periodic table to quickly refer to information about an element, like atomic mass ...
