Question 1: Explain in your own words why Dmitri Mendeleev's periodic table was considered a significant scientific breakthrough in the 19th century.

Answer: Mendeleev's periodic table organized elements based on their properties and atomic weights, allowing him to predict the existence and properties of undiscovered elements, which was a major advancement in understanding atomic structure.

Question 1: Define the term 'periodic law' as it relates to Mendeleev's periodic table.

Answer: The periodic law states that the properties of elements are periodic functions of their atomic weights (or atomic numbers in modern terms), leading to the arrangement of elements in a periodic table.

Question 2: Describe how Mendeleev predicted the properties of elements that had not yet been discovered.

Answer: Mendeleev observed gaps in his periodic table and predicted the properties of missing elements by examining trends in atomic weights and properties of neighboring elements, allowing him to estimate their atomic weights, densities, and chemical behaviors.

Question 1: In Mendeleev's periodic table, an element with an atomic weight of approximately 63 was placed in the same group as sulfur and selenium. Based on their properties, what element might this be, and what is its modern atomic number?

Answer: The element could be chlorine, which has an atomic number of 17. However, considering the atomic weight of about 63, it likely refers to bromine, which has an atomic weight close to 79 and atomic number 35.

Question 2: A newly discovered element in Mendeleev's table was predicted to have an atomic weight of 44 and properties similar to magnesium. What would be its probable position in the periodic table?

Answer: It would likely be placed in Group 2, near magnesium, with a predicted atomic weight around 44, which corresponds to calcium (atomic number 20).

Question 1: Calculate the density of an element if 10 grams occupy a volume of 5 cm³. Use the formula density = mass/volume. Provide your answer in g/cm³.

Answer: Density = 10 g / 5 cm³ = 2 g/cm³

Question 2: If an element's atomic weight is 23 and it has 11 protons, what is the number of neutrons in its most common isotope?

Answer: Number of neutrons = Atomic weight - number of protons = 23 - 11 = 12 neutrons

Question 1: Describe a safe laboratory procedure to test the reactivity of a metal with water.

Answer: First, wear safety goggles and gloves. Place a small piece of metal in a test tube with a measured amount of water. Observe any bubbling or temperature change. Ensure proper ventilation and dispose of chemicals according to safety guidelines.

Question 2: Identify two safety precautions that must be taken when handling reactive elements in the lab.

Answer: Wearing protective gloves and goggles, and working in a well-ventilated area or under a fume hood.

Question 1: Explain how Mendeleev's periodic table helped scientists predict the properties of undiscovered elements. (6 marks)

Answer: Mendeleev arranged elements in order of increasing atomic weight, grouping them by similar chemical properties. He left gaps for elements not yet discovered and predicted their properties based on trends observed in neighboring elements. This predictive ability validated the periodic law and advanced the understanding of atomic structure.

Question 1: Describe how Mendeleev's periodic table influences modern chemistry and industry today.

Answer: Mendeleev's periodic table laid the foundation for the modern periodic table based on atomic numbers. It helps chemists predict element properties, discover new elements, and develop new materials for industries such as electronics, medicine, and manufacturing.