Question

1. in mendeleevs new table, patterns in reactivity appeared to repeat after how many elements?
2. in mendeleevs periodic table, rows were called ____ and columns were called ____.

rows = columns =

1. give 2 reasons why mendeleevs periodic table was so revolutionary at the time. what made it great?
2. the discovery of gallium (ga) by paul emile lecoq de boisbaudran in 1875 first proved how useful and accurate mendeleevs periodic table of elements was. explain this statement.
3. what were the 3 other elements that mendeleev successfully predicted the existence of?

Explanation:

• Question 5: Mendeleev's table was based on periodicity. The reactivity patterns repeated after 8 elements (similar to the modern concept of periods where properties repeat after a certain number of elements in the early part of the table).
• Question 6: In Mendeleev's periodic table, rows were called periods and columns were called groups. This is a fundamental naming convention in the periodic table structure.
• Question 7:
• Prediction of new elements: Mendeleev left gaps in his table for elements he predicted would be discovered. For example, he predicted eka - silicon (which later became germanium).
• Correction of atomic masses: He used the periodic trends to correct the atomic masses of some known elements. For instance, he corrected the atomic mass of uranium based on its position in the table.
• Question 8: Mendeleev predicted an element he called eka - aluminium. Gallium, when discovered, had properties very close to what Mendeleev predicted for eka - aluminium. For example, Mendeleev predicted a density of around \(5.9 - 6.0\space g/cm^{3}\) and gallium has a density of \(5.907\space g/cm^{3}\). This showed that the periodic table could be used to predict the properties of yet - to - be - discovered elements.
• Question 9: Mendeleev successfully predicted the existence of eka - boron (scandium, Sc), eka - silicon (germanium, Ge), and eka - manganese (technetium, Tc, although technetium was discovered much later as it is radioactive and not found in nature in significant amounts).

Answer:

1. 8
2. Rows = periods; Columns = groups
3. - Predicted new elements (e.g., left gaps for them). - Corrected atomic masses of known elements.
4. Mendeleev predicted eka - aluminium. Gallium (discovered later) had properties (e.g., density, melting point) close to the predicted values of eka - aluminium.
5. Scandium (Sc), germanium (Ge), technetium (Tc)