Question

multiple choice 1 point
which element has the largest atomic radius: mg, ca, ba, sr?
ca
mg
sr
ba
clear my selection
4 multiple choice 1 point
arrange the isoelectronic series ions into the order of decreasing ionic radius: se²⁻, rb⁺, br⁻, sr²⁺.
sr²⁺ < rb⁺ < br⁻ < se²⁻
br⁻ < rb⁺ < se²⁻ < sr²⁺
sr²⁺< se²⁻ < rb⁺ < br⁻
se²⁻ > br⁻ > rb⁺ > sr²⁺
clear my selection

Explanation:

Question 3 (Which element has the largest atomic radius: Mg, Ca, Ba, Sr?)

Step1: Identify the group

Mg, Ca, Ba, Sr are all in Group 2 (alkaline earth metals).

Step2: Apply atomic radius trend

In a group, atomic radius increases as we move down the group (more electron shells are added). The order from top to bottom in Group 2 is Mg < Ca < Sr < Ba.

Step1: Determine electron configuration

All these ions are isoelectronic (have the same number of electrons, \( 36 \) electrons, same as Kr).

Step2: Analyze nuclear charge

For isoelectronic ions, ionic radius decreases with increasing nuclear charge (number of protons). The number of protons: \( \text{Se}^{2-} \) (34), \( \text{Br}^- \) (35), \( \text{Rb}^+ \) (37), \( \text{Sr}^{2+} \) (38).

Step3: Order by ionic radius

Larger negative charge (or smaller positive charge) leads to larger radius. So the order of decreasing ionic radius is \( \text{Se}^{2-} > \text{Br}^- > \text{Rb}^+ > \text{Sr}^{2+} \).

Answer:

D. Ba

Question 4 (Arrange the isoelectronic series ions into the order of decreasing ionic radius: \( \text{Se}^{2-} \), \( \text{Rb}^+ \), \( \text{Br}^- \), \( \text{Sr}^{2+} \))