4 THE PERIODIC TABLE
By arranging the elements in order of atomic weight (we now use relative atomic mass) he found that, if he left a few gaps, chemically related elements occurred at regular intervals. Mendeleev first published a version of his Periodic Table in 1869, in his textbook, Principles of Chemistry (Figure A1). His groupings showed the correct trends in properties and these were later confirmed by experiments. The gaps promoted a search for new elements. Mendeleev’s initial table arranged the elements in columns. He later changed the layout of his table to the version that we are familiar with today. The vertical columns correspond to the periods of elements in the modern Periodic Table and the horizontal rows are the groups of elements.
matched Mendeleev’s predicted properties for eka-silicon (listed in Table 1). Germanium was eka-silicon. In the 20 years that followed, more of Mendeleev’s predicted elements were discovered and his Periodic Table was accepted as an important tool for chemistry.
Questions A1. Mendeleev also left a gap in his Periodic Table under aluminium in Group 3(13). What element fitted this gap? A2. What events led to Mendeleev’s table being accepted by the scientific community? A3. The element rutherfordium (unnilquadium was renamed rutherfordium in 1997), Z = 104, is placed under hafnium in the Periodic Table. Why are scientists predicting that element 117 will be the first halogen to be made artificially? A4. Element 118 was confirmed in 2008. Into which group is it placed? A5. Explain the statement: Mendeleev filled in the gaps in his Periodic Table as new elements were discovered. Today, chemists are still adding to the Periodic Table.
Stretch and challenge
Figure A1 Mendeleev’s Periodic Table
Mendeleev had left a gap below silicon (Group 4 (14)) in his Periodic Table. He gave the unknown element the name eka-silicon and predicted its properties. When the element germanium was discovered, its properties closely
A6. Before Mendeleev’s table, John Newlands had attempted to organise the elements into a table. He listed them in order of relative atomic mass and noticed that elements eight places away from each other had similar properties – he arranged them in rows of eight. His table was known as Newland’s octaves. How far was his table successful, and where did it produce problems?
Silicon, Si
Predicted properties of eka-silicon, Ek
Actual properties of germanium, Ge
Relative atomic mass
28
72
72.59
Density/ g cm−3
2.3
5.5
5.3
Appearance
grey non-metal
grey metal
grey metal
Formula of oxide
SiO2
EkO2
GeO2
Reaction with non-oxidising acid
none
very slow
slow with concentrated acid
Table A1 The properties of silicon and germanium
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