Question

Compared with the alkaline earth metals, the alkali metals exhibit

• A. smaller ionic radii
• B. higher boiling points
• C. greater hardness
• D. lower ionisation energies

Answer 1

The Correct Option is D

To determine why the alkali metals exhibit lower ionization energies compared to alkaline earth metals, let's first understand the key properties of these two groups in the periodic table.

Both alkali metals (Group 1) and alkaline earth metals (Group 2) are found in the s-block of the periodic table:

• Alkali Metals: These include lithium (Li), sodium (Na), potassium (K), etc. They have a single electron in their outermost shell.
• Alkaline Earth Metals: These include beryllium (Be), magnesium (Mg), calcium (Ca), etc. They have two electrons in their outermost shell.

Ionization Energy is the energy required to remove an electron from a gaseous atom or ion. The factors affecting ionization energy include:

• Atomic size (radius)
• Nuclear charge
• Shielding effect

Let's analyze why alkali metals have lower ionization energies compared to alkaline earth metals:

1. Shielding Effect: Alkali metals, having one less electron compared to alkaline earth metals, experience more significant electron shielding, making it easier to remove the outermost electron.
2. Atomic Size: Alkali metals have a larger atomic radius than alkaline earth metals in the same period. This increased distance from the nucleus makes it easier to remove the outer electron.
3. Nuclear Charge: Though both groups belong to differing periods, the effective nuclear charge (positive charge affecting electrons) is relatively less impactful in alkali metals due to greater shielding, lowering the ionization energy.

These factors demonstrate that alkali metals possess lower ionization energies compared to alkaline earth metals, making it energetically favorable for alkali metals to lose their valence electron.

Let's briefly rule out the other options:

• Smaller Ionic Radii: Alkali metals actually have larger ionic radii compared to alkaline earth metals.
• Higher Boiling Points: Alkali metals have relatively lower boiling points than alkaline earth metals due to weaker metallic bonding.
• Greater Hardness: Alkali metals are softer and less hard than alkaline earth metals.

Thus, the correct answer is that alkali metals exhibit lower ionisation energies compared to alkaline earth metals.