Which atom has the highest first ionization energy k, Ca, P or Cl?
The Correct Answer and Explanation is:
Answer: Chlorine (Cl) has the highest first ionization energy among potassium (K), calcium (Ca), phosphorus (P), and chlorine (Cl).
Explanation:
First ionization energy is the amount of energy required to remove the outermost electron from a neutral atom in the gaseous state. It is influenced by several factors, including atomic size, nuclear charge, electron shielding, and the electron’s distance from the nucleus.
In the periodic table, ionization energy generally increases across a period (from left to right) and decreases down a group (from top to bottom). This trend can be explained through atomic structure:
- Across a Period (Left to Right): Atomic number increases, meaning more protons are present in the nucleus. As a result, the effective nuclear charge also increases, pulling electrons closer to the nucleus. This stronger attraction makes it more difficult to remove an electron, thereby increasing ionization energy.
- Down a Group (Top to Bottom): Atoms gain more electron shells, increasing the distance between the outermost electron and the nucleus. This added distance and increased shielding by inner electrons reduce the effective nuclear attraction, making it easier to remove an electron, thus lowering the ionization energy.
Applying these principles:
- Potassium (K) is in Group 1 and Period 4. It has a low ionization energy due to its large atomic size and a single valence electron in a new outer shell.
- Calcium (Ca) is in Group 2 and Period 4. Its ionization energy is slightly higher than potassium’s because it has a greater nuclear charge and a more stable electron configuration.
- Phosphorus (P) is in Group 15 and Period 3. It has a smaller atomic radius and a higher nuclear charge than both K and Ca, resulting in a higher ionization energy.
- Chlorine (Cl) is in Group 17 and Period 3. It has one of the highest ionization energies among the elements listed due to its small size and high effective nuclear charge.
Therefore, chlorine has the highest first ionization energy among the four atoms.
