Question 1: Dmitri Mendeleev arranged the elements based on increasing atomic mass and properties, leaving gaps for undiscovered elements. How did this organisation help predict the properties of missing elements?

Answer: It allowed Mendeleev to predict properties of undiscovered elements by observing periodic trends and gaps in the table.

Question 1: Define the term 'periodic table'.

Answer: A chart that organises elements based on their atomic number and properties in a repeating pattern.

Question 2: Explain why Mendeleev arranged elements in order of increasing atomic mass rather than atomic number.

Answer: Because the concept of atomic number was not known at the time, and arranging by atomic mass revealed periodic trends.

Question 3: Describe one limitation of Mendeleev's periodic table.

Answer: Some elements were placed out of order by atomic mass, causing inconsistencies; also, the atomic number was unknown.

Question 1: If the atomic mass of Tellurium (Te) is approximately 127.6 u and that of Iodine (I) is approximately 126.9 u, calculate the difference in atomic masses. Show your working.

Answer: Difference = 127.6 u - 126.9 u = 0.7 u

Question 1: Design a simple experiment to verify the periodic trend of increasing atomic radius down a group in the periodic table. Include variables and safety precautions (theory only).

Answer: To verify the trend, compare atomic radii of elements in the same group (e.g., alkali metals). Variables include element type (independent), atomic radius (dependent). Safety precautions involve handling chemicals with gloves and eye protection. Use appropriate measurement techniques such as X-ray diffraction or electron microscopy in a lab setup.

Question 1: A gap in Mendeleev's table was later filled by the discovery of Gallium, which has an atomic mass of approximately 69.7 u. Explain how this discovery supported Mendeleev's predictions.

Answer: It confirmed Mendeleev's prediction of an element with similar properties to aluminium, validating his organisation based on periodic trends.

Question 1: Discuss the significance of Mendeleev's periodic table in the development of modern chemistry. Include at least three key points in your answer.

Answer: Mendeleev's periodic table was significant because it organised elements based on properties and atomic mass, allowing for the prediction of undiscovered elements. It provided a systematic framework that influenced the development of the modern periodic table based on atomic number. His work helped chemists understand periodic trends, leading to advances in chemical theory and element discovery.

Question 1: Describe how the concept of periodicity based on Mendeleev's organisation is used in the development of new materials or pharmaceuticals today.

Answer: Modern chemists use periodic trends such as atomic size and reactivity, predicted from Mendeleev's organisation, to design new materials and drugs with desired properties, improving efficiency and safety in development.