Helpful steps?

Calculate the predicted atomic radius for potassium, K, given the atomic radius of rubidium, Rb, (0.247 nm) and cesium, Cs, (0.265 nm).

we only subtract 0.265 out off 0.247 to find the radius decreases from period 6 to period 5. so the answer is = 0.018 nm.

0.229nm

To calculate the predicted atomic radius for potassium (K) based on the atomic radii of rubidium (Rb) and cesium (Cs), you can follow these steps:

Step 1: Note down the given atomic radii of rubidium (Rb) and cesium (Cs):
- Atomic radius of Rb = 0.247 nm
- Atomic radius of Cs = 0.265 nm

Step 2: Observe the trend in atomic radii within a group (column) of the periodic table.
- Atomic radius generally increases as we move down a group.

Step 3: Compare the positions of rubidium (Rb), cesium (Cs), and potassium (K) in the periodic table.
- Rubidium and cesium are located below potassium in the same group (Group 1 or alkali metals).

Step 4: Analyze the trend in atomic radii within the alkali metal group:
- Since atomic radius generally increases down a group, we can expect the atomic radius of potassium (K) to be less than that of cesium (Cs) but greater than that of rubidium (Rb).

Step 5: Calculate an estimate for the atomic radius of potassium (K) using the given values:
- To calculate, you can take an average of the atomic radii of rubidium (Rb) and cesium (Cs). Add the two values and divide the sum by 2.

Predicted atomic radius of K = (Atomic radius of Rb + Atomic radius of Cs) / 2

Predicted atomic radius of K = (0.247 nm + 0.265 nm) / 2

Step 6: Perform the calculation and find the predicted atomic radius for potassium (K):
- Add the atomic radii and divide by 2:

Predicted atomic radius of K = (0.247 nm + 0.265 nm) / 2
Predicted atomic radius of K = 0.256 nm

Therefore, the predicted atomic radius for potassium (K) is approximately 0.256 nm.

If that's the only information available to you I would suggest that you subtract 0.265-0.247 to find how much the radius decreases from period 6 to period 5 and subtract that difference from Rb to make an educated guess at K that's down one more period.