Question

of elements from period 3 and group 17. number the elements sodium, magnesium, and potassium in the predicted order of ionic radius from the largest (1) to the smallest (3). sodium magnesium potassium done

Explanation:

Step1: Recall ionic - radius trends

Ionic radius increases down a group and decreases across a period for cations. Potassium is in Group 1 and Period 4, sodium is in Group 1 and Period 3, and magnesium is in Group 2 and Period 3.

Step2: Analyze potassium

Potassium forms a $K^+$ ion. Since it is in Period 4, it has more electron - shells than sodium and magnesium, so it has the largest ionic radius among them.

Step3: Analyze sodium and magnesium

Sodium forms a $Na^+$ ion and magnesium forms a $Mg^{2 + }$ ion. Both are in Period 3. But magnesium has a higher nuclear charge (+2) compared to sodium's (+1) for their respective ions. So, $Mg^{2 + }$ has a smaller ionic radius than $Na^+$.

Answer:

1. potassium
2. sodium
3. magnesium