Question 1: Who was Dmitri Mendeleev and what was his main contribution to Chemistry?

Answer: Dmitri Mendeleev was a Russian chemist who created the first periodic table by arranging elements based on atomic mass and properties.

Question 2: Explain the significance of the periodic law as proposed by Mendeleev.

Answer: The periodic law states that the properties of elements are the periodic functions of their atomic masses, leading to the organised arrangement of elements.

Question 1: Calculate the average atomic mass of an element that has isotopes with masses 20.0 u (90% abundance) and 22.0 u (10% abundance). Use the formula: Average atomic mass = (mass1 × abundance1 + mass2 × abundance2) / 100.

Answer: 21.8

Question 2: If an element's atomic mass is approximately 23 u and it was placed in Mendeleev's table based on atomic mass, which element could it be? (Hint: Think of common elements with atomic masses close to 23).

Answer: Sodium (Na)

Question 1: Describe a safe laboratory procedure for testing the reactivity of different metals with hydrochloric acid.

Answer: Wear protective goggles and gloves, add small pieces of metal to acid in a test tube, and observe the reaction while keeping the area well ventilated.

Question 2: Identify two variables that would affect the outcome of an experiment testing element reactivity, and suggest how to control them.

Answer: Variables include temperature and concentration of acid; control by keeping temperature constant and using a standard acid concentration.

Question 1: A scientist observes that element X, with an atomic mass of 65 u, exhibits properties similar to iodine but is placed in a different group in Mendeleev's table. What could be the reason for this discrepancy?

Answer: The element may be an isotope or the atomic mass used initially was inaccurate; Mendeleev's arrangement was based on atomic mass, but properties guided placement.

Question 2: Explain how Mendeleev’s periodic table helped in predicting the discovery of new elements.

Answer: Mendeleev left gaps in his periodic table where properties of undiscovered elements could be predicted based on trends. When new elements were discovered, their properties matched predictions, confirming the table's validity.

Question 1: Describe how Mendeleev arranged the elements in his periodic table and explain the importance of the gaps he left.

Answer: Mendeleev arranged elements in order of increasing atomic mass and grouped them by similar properties. He left gaps for elements not yet discovered, predicting their properties, which validated his table later.

Question 1: How did Mendeleev's periodic table influence modern chemistry and the development of the periodic table used today?

Answer: Mendeleev's organisation based on atomic mass and properties laid the groundwork for the modern periodic table, which is now based on atomic number, enabling better understanding of element relationships.

Question 2: Discuss a modern technology or industry that relies on the principles of the periodic table originally developed by Mendeleev.

Answer: Nuclear medicine relies on understanding isotopes and atomic properties that were predicted and organised through the periodic table, enabling development of medical imaging and radiotherapy.