Question

Which of the following has maximum ionization potential? (a) \(\mathrm{Al}\) (b) \(\mathrm{P}\) (c) Si (d) \(\mathrm{Mg}\)

Short answer

Phosphorus (P) has the maximum ionization potential.

Step-by-step solution

Understand Ionization Potential

Ionization potential (or ionization energy) is the energy required to remove an electron from a neutral atom in its gaseous state. It generally increases across a period from left to right due to increasing nuclear charge and decreases down a group due to the added electron shells.

Identify Elements in Their Periodic Trend

The elements given are (a) Al (Aluminum), (b) P (Phosphorus), (c) Si (Silicon), (d) Mg (Magnesium). All these elements belong to the third period (row) of the periodic table with the order: Mg, Al, Si, P.

Analyze Trends Within the Period

In the third period, as you move from left to right, the ionization potential generally increases. This is due to the increased effective nuclear charge, pulling the valence electrons closer and making them harder to remove.

Determine the Element with Maximum Ionization Potential

Among the given options, Phosphorus (P) is located farthest to the right in the periodic table, following Magnesium (Mg), Aluminum (Al), and Silicon (Si). Hence, Phosphorus will have the highest ionization potential due to a greater effective nuclear charge.

Key concepts

Periodic Trends

The concept of periodic trends helps us understand the properties of elements and how they change across the periodic table. One of these properties is ionization potential, which is the energy needed to remove an electron from an atom. As you go from left to right across a period (row), the ionization potential generally increases.

• This increase is due to the rise in effective nuclear charge. The nucleus pulls electrons more strongly as more protons are added.
• Additionally, the electrons remain in the same energy level, so there's no increase in electron shielding.

This makes it harder to remove an electron. Meanwhile, the ionization potential decreases as you go down a group (column) because the outer electrons are further from the nucleus, and electron shielding by inner electrons increases.

Third Period Elements

The third period of the periodic table includes elements from Sodium (Na) to Argon (Ar). In our exercise, the elements Magnesium (Mg), Aluminum (Al), Silicon (Si), and Phosphorus (P) are part of this period.

• As elements move across this period, from left to right, they show a trend of increasing ionization energies.
• This is attributed to the constant addition of protons increasing the effective nuclear charge, along with the electrons being placed in the same energy shell.

Phosphorus, being further to the right of Silicon, Magnesium, and Aluminum, has the highest ionization energy among them due to these trends.

Effective Nuclear Charge

Effective nuclear charge (denoted as \( Z_{ ext{eff}} \)) is crucial to understanding why the ionization potential changes across the periodic table. It is the net positive charge experienced by electrons in the valence shell.

• This charge increases as you move across a period because additional protons in the nucleus enhance its pull on electrons.
• The increased charge results in electrons being held more tightly, boosting ionization energy.
• The effective nuclear charge can be estimated by subtracting the shielding effect caused by inner electrons from the total number of protons.

In the third period, phosphorus has the highest effective nuclear charge among the given elements, making it the hardest for its electrons to be removed. That's why it possesses the maximum ionization potential in this set.