Mendeleev left gaps in his Periodic Table for elements that had not been discovered yet. He used the periodic trends of known elements to predict the properties of these missing elements.
He called one of these predicted elements "eka-silicon".
Table 1: Predicted properties of 'eka-silicon'
| Property | Predicted Value |
|---|---|
| Appearance | Grey metalloid with a high melting point |
| Melting Point (∘C^\circ\text{C}∘C) | Around 900∘C900^\circ\text{C}900∘C |
| Relative Atomic Mass | 727272 |
| Density (g/cm3\text{g/cm}^3g/cm3) | 5.55.55.5 |
Table 2: Properties of three elements discovered later
| Element | Appearance | Melting Point (∘C^\circ\text{C}∘C) | Relative Atomic Mass | Density (g/cm3\text{g/cm}^3g/cm3) |
|---|---|---|---|---|
| Gallium (Ga) | Silver-grey metal | 29.829.829.8 | 69.769.769.7 | 5.915.915.91 |
| Germanium (Ge) | Grey-white metalloid | 938938938 | 72.672.672.6 | 5.325.325.32 |
| Selenium (Se) | Grey non-metal | 221221221 | 79.079.079.0 | 4.814.814.81 |
Which element matches Mendeleev's predictions for 'eka-silicon'?
Give two reasons for your answer to part (a).
Mendeleev did not predict the existence of Neon (Ne\text{Ne}Ne). The electron configuration of a neon atom is 2,82, 82,8. Describe and explain the reactivity of neon based on this electron arrangement.
Neon has two common stable isotopes: 1020Ne{}^{20}_{10}\text{Ne}1020Ne and 1022Ne{}^{22}_{10}\text{Ne}1022Ne. State the number of protons, neutrons, and electrons in a neutral atom of each isotope.