Mendeleev left a gap below aluminium in his Periodic Table. He predicted the properties of the missing element. Gallium was discovered a few years later.
| Property | Mendeleev's prediction | Gallium |
|---|---|---|
| Relative atomic mass | 68 | 69.7 |
| Density (g/cm3\mathrm{g/cm^{3}}g/cm3) | 5.9 | 5.9 |
| Formula of oxide | E2O3\mathrm{E_{2}O_{3}}E2O3 | Ga2O3\mathrm{Ga_{2}O_{3}}Ga2O3 |
Which conclusion is best supported by this evidence?
The difference in relative atomic mass showed that Mendeleev's Periodic Table was wrong.
The close match showed that elements must always be placed strictly in order of relative atomic mass.
The close match proved that elements should be placed in order of atomic number.
The close match supported Mendeleev's idea of leaving gaps for undiscovered elements that fit the pattern of properties in each group.
64 exam-style questions on OCR GCSE Chemistry 2.2 Bonding, covering 2.2.1 Metals, non-metals and the Periodic Table, 2.2.2 Types of chemical bonding and dot and cross diagrams, 2.2.3 Limitations of bonding models, and 2.2.4 Reactivity, atomic number and the modern Periodic Table. Each one has a worked solution and a mark scheme showing where the marks go.