9/13/2023 0 Comments Atomic number 9At the time, the nucleus had not yet been found, and no one knew how the inside of an atom was put together, so atomic mass was the only way to organise the elements. In Dimitri Mendeleev’s first periodic table, published in 1869, the elements were arranged in order of increasing atomic mass. In other words, the properties of chemical elements tend to repeat themselves over and over again as their mass goes up. All of the elements in Group 8A are nonreactive monatomic gases at room temperature. For example, all of the elements in Group 1A are soft metals that react violently with water and make 1+ charges. In an atomic number-based periodic table, elements with similar chemical properties tend to fall into the same column (group). The number of protons tells us what an element is (i.e., an element with 6 protons is a carbon atom, no matter how many neutrons may be present). The number of protons in the nucleus of an atom is its atomic number. The elements on the modern periodic table are listed in order of increasing atomic number.
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