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In the 19th and 20th centuries, experimental results showed scientists that atoms consist of a positive, heavy nucleus which is surrounded by electrons - CIE - A-Level Chemistry - Question 1 - 2010 - Paper 1
Question 1
In the 19th and 20th centuries, experimental results showed scientists that atoms consist of a positive, heavy nucleus which is surrounded by electrons. Then in the... show full transcript
Worked Solution & Example Answer:In the 19th and 20th centuries, experimental results showed scientists that atoms consist of a positive, heavy nucleus which is surrounded by electrons - CIE - A-Level Chemistry - Question 1 - 2010 - Paper 1
Step 1
Label the energy levels to indicate the principal quantum number and the type of orbital at each energy level.
Answer
The energy levels should be labeled as follows:
- The highest energy level is numbered as 2, representing the 2s orbital, which is spherical.
- The following levels include the 2p orbitals, labeled as 2pₓ, 2pᵧ, and 2p₂ as they are oriented along the x, y, and z axes respectively.
- The lowest energy level is the 1s orbital, also spherical and labeled as 1s.
Step 2
On the axes below, draw a sketch diagram of one of each different type (shape) of orbital that is occupied by the electrons in a second-period element.
Answer
The diagrams should depict:
- A spherical s orbital represented as a circle centered on the origin, labeled 's'.
- A double-lobed p orbital, represented as two lobes extending along one axis, labeled 'p'. These lobes should be aligned along the designated x, y, or z axis.
Step 3
Complete the electronic configurations of nitrogen atoms and oxygen atoms on the energy level diagrams below.
Answer
For nitrogen (7 electrons):
-
The configuration is filled as follows:
2↑↓
2pₓ
2pᵧ
(2s ↑↓) (1s ↑↓)
For oxygen (8 electrons):
-
The configuration is:
2↑↓ 2pₓ
2pᵧ ↑ (2s ↑↓) (1s ↑↓)
Both diagrams must accurately represent the occupied orbitals with the correct spin orientation.
Step 4
Step 5
Explain, with reference to (a)(iii), the relative values of these two ionisation energies.
Answer
The relative ionisation energies can be explained by considering electron configuration and stability:
- Nitrogen has three unpaired electrons in its 2p orbitals, making it more stable due to symmetry and minimizing electron-electron repulsion.
- Oxygen has two paired electrons in one of its 2p orbitals, which leads to increased repulsion between electrons, thus requiring less energy to remove an electron.
Therefore, this difference in electron configuration accounts for the higher ionisation energy of nitrogen compared to oxygen.