In 1869, Dmitri Mendeleev arranged the elements that were known at the time into a table.
He mainly arranged the elements in order of increasing atomic mass.
The table shows information about four elements.
| Element | Relative atomic mass (Ar) | Atomic number |
|---|---|---|
| argon | 39.9 | 18 |
| potassium | 39.1 | 19 |
| tellurium | 127.6 | 52 |
| iodine | 126.9 | 53 |
Mendeleev placed tellurium before iodine in his table, even though tellurium has a higher relative atomic mass.
Suggest why he did this.
Argon was discovered in 1894, after Mendeleev's table was published.
Use the data to explain why argon would have been difficult to place in a table arranged only in order of atomic mass.
In the modern Periodic Table, elements are arranged in order of atomic number.
Explain, in terms of protons and electrons, why argon is placed in Group 0 and potassium is placed in Group 1.
Mendeleev left gaps in his table. He predicted the properties of an undiscovered element that he called eka-silicon, Es.
In 1886, the element germanium, Ge, was discovered.
The table compares Mendeleev's predictions with the properties of germanium.
| Property | Mendeleev's prediction for eka-silicon (1871) | Germanium (discovered 1886) |
|---|---|---|
| relative atomic mass | 72 | 72.6 |
| density (g/cm³) | 5.5 | 5.3 |
| formula of oxide | EsO₂ | GeO₂ |
| boiling point of chloride (°C) | below 100 | 86 |
Evaluate how well this evidence supported Mendeleev's table.
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.