Question

Why does Barium (Ba) have a larger atomic radius than Magnesium (Mg)?

A. All of these.
B. The nucleus of barium (Ba) repels the electrons with more force than in magnesium (Mg), pushing them further away from the nucleus.
C. Barium (Ba) has more energy shells for electrons than magnesium (Mg).
D. Barium (Ba) has more neutrons than magnesium (Mg).

Answer 1

C. Barium (Ba) has more energy shells for electrons than magnesium (Mg).

Even B could be correct, but nucleus doesn't repel electrons, but it attracts electrons. Electrons repel electrons

Step-by-step explanation:

Barium and Magnesium are both in Group II

Down the group, nuclear charge increases due to increase in atomic number (addition of protons). But the screening/shielding effect increases down the group since electrons are added to the different energy levels. But the increase in screening effect outweighs the increase in nuclear charge

As a result, Effective nuclear Charge decreases hence atomic radius increases from Barium to Magnesium

- Nuclear charge is the force of attraction by the nucleus towards incoming electrons (nuclear attraction)

Glossary:

- Screening/shielding effect is the tendency of electrons repel the incoming electrons.

- Effective nuclear charge is the overall nuclear attraction of an atom.

Answer 2

The correct answer is C: Barium (Ba) has more energy shells for electrons than magnesium (Mg).

Atomic radius is defined as the distance from the nucleus to the outermost electron shell of an atom. The atomic radius of an element is affected by various factors such as the number of protons in the nucleus, the number of electrons present in the atom, and the energy levels or shells occupied by the electrons.

In this case, the atomic radius of Barium (Ba) is larger than that of Magnesium (Mg) because Barium has more energy shells for electrons than Magnesium. As we move down a group in the periodic table, the number of energy shells increases. Since Barium is located below Magnesium in the periodic table, it has more energy shells than Magnesium. This causes the atomic radius of Barium to be larger than that of Magnesium.