Why is ionization energy for calcium greater than that for potassium?

The two electrons of Ca are in the same orbital as the one electron from K so the distance is the same from the outside shell to the nucleus.

On Ca there are 18 electrons between the two outside electrons and the inner 20+ nuclear charge so the outside electrons have a net of 2+ charge attracting them (20+ nuclear - 18- shieding electrons between = 2+ net charge.
For K there are the same number of shielding electrons (18) so the net attraction for the one outside electron of K is +19 - 18- = 1+ net charge. So the attraction between the outside electrons is higher for Ca which makes the ionization energy higher for Ca.

The ionization energy of an atom refers to the amount of energy required to remove an electron from its outer shell and convert it into a positively charged ion. The ionization energy generally increases as you move across a period from left to right in the periodic table, and it decreases as you move down a group.

Calcium (Ca) is located to the left of potassium (K) in the periodic table. Therefore, calcium has a smaller atomic number and fewer occupied energy levels compared to potassium. This difference in electron configuration contributes to the higher ionization energy of calcium compared to potassium.

To determine the exact ionization energies of calcium and potassium, you can refer to a periodic table or look up the values in a reliable database. Here's how to do it:

1. Access a reliable source: Consult a reputable chemistry textbook, reference book, or an online database that provides accurate and up-to-date information on ionization energies. One popular database is the National Institute of Standards and Technology (NIST) Chemistry WebBook.

2. Locate the elements: Find the positions of calcium (Ca) and potassium (K) on the periodic table.

3. Identify the ionization energy values: Look for the specific ionization energy values associated with each element. These values are typically presented in units of kilojoules per mole (kJ/mol) or electron volts (eV).

4. Compare the values: Compare the ionization energies of calcium and potassium. You will find that calcium has a higher ionization energy than potassium due to its electron configuration.

Remember that ionization energy is influenced by factors such as atomic radius, electron shielding, and the effective nuclear charge experienced by the outermost electron. By understanding the position of elements in the periodic table and their electronic structures, you can explain why calcium has a higher ionization energy than potassium.