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Elements in Ancient and Medieval Times Dalton’s elements (1809)
Periodic Table of Elements - History During the nineteenth century, chemists began to categorize the elements according to similarities in their physical and chemical properties. The end result of these studies was our modern periodic table. Johann Doebereiner In 1829, J. Doebereiner classified some elements into groups of three, which he called triads. The elements in a triad had similar chemical properties and orderly physical properties (MODEL OF TRIADS): [Cl 2, Br 2, I 2 ], [P, As, Sb], [Li, Na, K] and [Ca, Sr, Ba]. John Newlands In 1863, J. Newlands suggested that elements may be arranged in “octaves” because he noticed (after arranging the elements in order of increasing atomic mass) that certain properties repeated every 8 th element (LAW OF OCTAVES).
Telluric Helix of Screw (A. de Chancourtois) (1862) A. de Chancourtois
Periodic Table of Elements - History In 1869 Dmitri Mendeleev published a table of the elements organized by increasing atomic mass. At the same time, Lothar Meyer published his own table of the elements organized by increasing atomic mass, Dmitri Mendeleev Lothar Meyer Both Mendeleev and Meyer arranged the elements in order of increasing atomic mass. Both left vacant spaces where unknown elements should fit. So why is Mendeleev called the “father of the modern periodic table” and not Meyer, or both?
Original Periodic Table of the Elements Mendeleev stated that if the atomic weight of an element caused it to be placed in the wrong group, then the weight must be wrong. (He corrected the atomic masses of Be, In, and U). He used the table to predict the physical properties of three elements that were yet unknown (Sc, Ge, Ga, Tc). When properties of these elements turned out to be very close to the predicted ones by Mendeleev, his table was widely accepted. Periodic Table of Elements - History
However, in spite of Mendeleev’s great achievement, problems arose when new elements were discovered and more accurate atomic weights determined. By looking at our modern periodic table, can you identify what problems might have caused chemists a headache? Periodic Table of Elements - History Henry Moseley (1913) rearranged the elements in order of increasing atomic number. Henry Moseley Ar and K Co and Ni Te and I Th and Pa
Modern Periodic Table of the Elements
Different modern versions of Periodic Table Round Table of Elements Fractal Table of Elements
Different modern versions of Periodic Table
Energetic blocks in Periodic Table 1s 2s 2p 3s 3p 4s 3d
Physical properties of elements in the Periodic Table 88 metals 17 nonmetals 7 metalloids
Ionization energy The ionization energy (E I ) of an atom or molecule is the minimum energy required to remove (to infinity) an electron from the atom or molecule isolated in free space and in its ground electronic state.
Electronegativity in Periodic Table Electronegativity, symbol χ (the Greek letter chi), is a chemical property that describes the ability of an atom to attract electrons towards itself. E d (AB) – dissociation energy (eV)
Van der Waals radius: half the minimum distance between the nuclei of two atoms of the element that are not bound to the same molecule. Ionic radius: the radius of the ions deduced from the spacing of atomic nuclei in crystalline salts that include that ion. The length of the ionic bond should equal the sum of their ionic radii. Covalent radius: the radius of the atoms of an element when covalently bound to other atoms, as deduced the separation between the atomic nuclei in molecules. The length of a covalent bond should equal the sum of their covalent radii. Metallic radius: the radius of atoms of an element when joined to other atoms by metallic bonds. Atomic radius
Cations are smaller than corresponding atoms. Anions are larger than corresponding atoms. II/
Due to increased attraction Larger nuclear charge II/
Factors affecting the atomic radius:
T melt. [ºC] Melting point Melting point for a solid is the temperature at which the solid and liquid phases exist in equilibrium.