Questions: Which atom should be larger? Francium (Fr), Barium atom (Ba), Barium ion (Ba+2), Uranium (U)

Solution Steps

Atomic size generally increases as you move down a group in the periodic table due to the addition of electron shells. For ions, the size can be affected by the loss or gain of electrons. Cations (positively charged ions) are typically smaller than their neutral atoms because they lose electrons, reducing electron-electron repulsion.

• Francium (Fr): Francium is in Group 1 and is the heaviest alkali metal. It has a large atomic radius due to its position at the bottom of the periodic table.
• Barium (Ba): Barium is in Group 2 and is also near the bottom of the periodic table, but it is not as far down as Francium.
• Barium ion ($\mathrm{Ba}^{2+}$): The Barium ion has lost two electrons, which significantly reduces its size compared to the neutral Barium atom.
• Uranium (U): Uranium is an actinide and has a large atomic radius, but it is not as large as Francium due to its position in the f-block.

Given the positions in the periodic table and the nature of ions:

• Francium (Fr) is expected to have the largest atomic radius because it is the heaviest alkali metal.
• Barium (Ba) is smaller than Francium but larger than the Barium ion.
• The Barium ion ($\mathrm{Ba}^{2+}$) is the smallest due to the loss of two electrons.
• Uranium (U) is large but not as large as Francium.

Final Answer