Mendeleev & The Periodic Table

Mendeleev for a Day Activity

Mendeleev’s Table

• Organized elements by increasing atomic mass so that elements with similar properties were in the same column.

Mendeleev’s Prediction

• After Mendeleev placed all the known elements in his periodic table, several empty spaces were left.

• In 1871 Mendeleev predicted the existence and properties of elements that would fill three of the spaces.

• By 1886, all three of these elements had been discovered.

Mendeleev’s Prediction

• Predicted Eka-aluminum in 1871– Soft metal– Low melting point– Density of 5.9 g/cm3

• Found: Gallium in 1875– Soft metal

– Melting Point 29.7 C

– Density of 5.91 g/cm3

Mendeleev’s Predictions

Usefulness of His Table

• The close match between Mendeleev’s prediction and the actual properties of new elements showed how useful his periodic table could be.

Henry Moseley

(1913, British)

– Organized elements by increasing atomic

number.

– Fixed problems in Mendeleev’s arrangement.