Question 1: Electronic structure describes the arrangement of electrons in an atom's orbitals. This arrangement determines the atom's chemical properties and reactivity.

Answer: Electronic structure is the distribution of electrons in an atom's orbitals, influencing its chemical behaviour.

Question 1: Define the term 'electron configuration'.

Answer: Electron configuration is the arrangement of electrons in an atom's orbitals expressed in a specific order.

Question 2: Explain why electrons occupy different energy levels or shells around the nucleus.

Answer: Electrons occupy different energy levels to minimise repulsion and to achieve a stable, low-energy state, following the Aufbau principle.

Question 1: Calculate the total number of electrons in a sulphur atom, given its atomic number is 16.

Answer: 16

Question 2: Write the electron configuration for a neon atom (atomic number 10).

Answer: 1s² 2s² 2p⁶

Question 1: Outline the steps of a practical experiment to observe hydrogen emission spectra, including the variables involved and safety precautions.

Answer: The experiment involves passing electrical discharge through hydrogen gas in a sealed tube, observing the emitted light through a spectroscope. Variables include gas pressure and voltage. Safety precautions include ensuring proper ventilation, wearing safety goggles, and handling electrical equipment carefully.

Question 1: A sodium atom has an electron configuration of 1s² 2s² 2p⁶ 3s¹. Explain how this configuration accounts for its chemical reactivity.

Answer: The single electron in the 3s orbital makes sodium highly reactive, as it can easily lose this electron to achieve a stable noble gas configuration (neon). This tendency to lose electrons underlies sodium's reactivity.

Question 1: Explain the Aufbau principle and how it determines the order in which electrons fill atomic orbitals. (6 marks)

Answer: The Aufbau principle states that electrons fill atomic orbitals starting from the lowest energy level and move to higher levels. This order is determined by the increasing energy of orbitals, following the sequence 1s, 2s, 2p, 3s, 3p, 4s, etc. This filling order explains electron configurations and the relative stability of atoms.

Question 2: Which of the following elements has the electron configuration 1s² 2s² 2p⁶ 3s² 3p⁶? (a) Sodium (b) Magnesium (c) Argon (d) Calcium

Answer: Argon

Question 1: Discuss how knowledge of electronic structures is utilised in the development of semiconductors and their role in electronic devices.

Answer: Understanding electronic structures allows scientists to manipulate the energy levels and electron behaviour in semiconductors, enabling the design of materials with specific electrical properties crucial for transistors, diodes, and integrated circuits used in almost all electronic devices.