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prep 2 les /1 periodic table
Attempts of Elements Classification 1-to be easily studied 2-find the relation between elements and their physical and chemical properties. Mendeleev`s table: He discovered that the elements were arranged in an ascending order according to their atomic weights from left to right in the horizontal rows. disadvanges of Mendeleev`s table: 1-He had to make a disturbance in the ascending order of atomic weights for some elements due to putting them in groups which suit their properties. 2-he also would have to deal with the isotopes of one element as different elements because they are different in their atomic weights. Advantages: 1- Mendeleev predicted the ability of discovering new elements so he left spaces (empty cells) in his table. 2- He corrected the wrong estimated atomic weights of some elements. Moseley `s table: 1- Moseley rearranged the elements in an ascending order according to their atomic number. 2- Added the inert gases in the (0) zero group. 3- classified each main group into two subgroups (A , ![]() 4- he allocated a place below his periodic table for the two groups lanthanides and actinides What is the scientific principle on which the classification of the elements based on? • Mendeleev’s periodic table: .................................................. .................................................. • Moseley’s periodic table............................................. .................................................. .. Note; 1-Rutherford discovered that the nucleus of atom contains positively charged protons 2-Moseley discovered in the same year after studying the properties of X rays that the periodicity of elements properties is related to their atomic number not their atomic weights. Modern periodic table: 1-Bohr discovered the main energy levels they are 7. 2-main energy level consists of a number of energy levels known as the energy sublevels. Description: 1-Elements are classified in the modern periodic table according to Their atomic numbers the way of filling the energy sublevels with electrons. 2- The number of known elements until now are 116 elements, 92 elements are abundant in The earth’s crust, the rest of the elements are prepared artificially. 3-Elements of (A) groups lie on the left and right of the table; you can locate their position.in the modern periodic table by knowing their atomic numbers and vice versa. 4-The elements of ( ![]() Determination the position of element in the table: 1-Number of period of the element = Number of energy levels. 2-Number of the group of the element = Number of electrons in the outermost energy level. |
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