who invented the periodic table - Dmitri Mendeleev, what is a period - a group of elements that are in a row with increasing atomic numbers, what is a group - a group of elements that are up/down in a column, how many elements are in the periodic table - 118, periodic table - all the chemical elements that have been discovered arranged in rows and columns, how elements change going down a column (group) - they all havshare common properties, such as melting point and boiling point, how elements change going across a row (period) - the atomic number increases,

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