Question

Write the electronic configuration of the Na +, Mg2 +, Ca2 + and Rb + ions. Research the size of these ions in picometers and order them in descending order of their size.

a) Na+: 1s² 2s² 2p⁶ 3s² 3p⁶
b) Mg2+: 1s² 2s² 2p⁶ 3s²
c) Ca2+: 1s² 2s² 2p⁶ 3s² 3p⁶ 4s²
d) Rb+: 1s² 2s² 2p⁶ 3s² 3p⁶ 4s² 3d¹⁰ 4p⁶ 5s¹

Answer 1

The electronic configurations for Na+, Mg2+, Ca2+, and Rb+ are obtained by removing electrons from the outermost shell of their neutral atoms. The size of ions generally decreases with increasing positive charge and decreases across a period, while increasing down a group in the periodic table.

Step-by-step explanation:

The electronic configurations of the given ions are as follows:

• Na+: 1s² 2s² 2p⁶ (loses one electron from 3s)
• Mg2+: 1s² 2s² 2p⁶ (loses two electrons from 3s)
• Ca2+: 1s² 2s² 2p⁶ 3s² 3p⁶ (loses two electrons from 4s)
• Rb+: 1s² 2s² 2p⁶ 3s² 3p⁶ 3d¹⁰ 4s² 4p⁶ (loses one electron from 5s)

To order these ions by size in picometers in descending order, we must consider that ions lose size when they lose electrons, due to a decreased electron cloud and increased effective nuclear charge. Typically, the size decreases across a period and increases down a group. Therefore, the order from largest to smallest is generally Rb+ > Ca2+ > Na+ > Mg2+.