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Reference.org
Mendeleev's predicted elements
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<p><a href="/facts/Dmitri_Mendeleev/xdouRrx8">Dmitri Mendeleev</a> published a <a href="/facts/Periodic_table/umdGIfUb">periodic table</a> of the <a href="/facts/Chemical_element/0jducgWD">chemical elements</a> in 1869 based on properties that appeared with some regularity as he laid out the elements from lightest to heaviest. When Mendeleev proposed his periodic table, he noted gaps in the table and predicted that then-unknown elements existed with properties appropriate to fill those gaps. He named them eka-boron, eka-aluminium, eka-silicon, and eka-manganese, with respective atomic masses of 44, 68, 72, and 100. </p>