Niels Bohr received the Nobel Prize for physics in 1922 for his model of the electronic structure of the atom - Junior Cycle Science - Question f - 2006

To determine the electron arrangement for an atom of potassium (K) with atomic number 19, we follow the Aufbau principle, which states that electrons fill atomic orbitals starting from the lowest energy level.

1. First Energy Level: This can hold a maximum of 2 electrons, filling it completely.

   • Electrons: 2

2. Second Energy Level: This can hold a maximum of 8 electrons, which also fills fully.

   • Electrons: 8

3. Third Energy Level: This level can hold up to 18 electrons. However, for potassium, we will fill it with just 8 electrons (since 2 + 8 + 8 = 18) and place the remaining 1 electron in the next shell.

   • Electrons: 8

4. Fourth Energy Level (Valence): This contains the remaining 1 electron.

   • Electrons: 1

Combining these values, the electron arrangement for potassium can be summarized as:

• 2, 8, 8, 1

This indicates that potassium has 2 electrons in the first shell, 8 in the second, 8 in the third, and 1 in the outermost shell.