# I'm getting two different answers for the atomic radius of iridium

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1. Dec 6, 2017

### Bobs

I'm getting too different answers for atomic radius of iridium. I've already found 1.34 x 10-8 but all shows different answers. I mean like 1.34, 1.35, 1.36... Are those correct?

2. Dec 6, 2017

### Staff: Mentor

I would say they are quite similar. The value of the atomic radius is something that depends on the way you define it (atom doesn't have a sharp edge) and the measurement method (and let's not forget about the measurement accuracy).

3. Dec 6, 2017

### Bobs

However, are those correct? or is there only an answer? It seems like different on wikipedia and others.

4. Dec 6, 2017

### Bobs

For BCC;

a = 4r/√3

mass of Ba atom = 137.327 g/mol

mass of 1 atom = 137.327 g / 6.022 x 1023 = 2.28 x 10-22 g

density of bulk = density of unit cell

total no. of Ba atoms in BCC = 2 atom

mass of 2 atom = 2 x 2.28 x 10-22 g = 4.56 x 10-22 g

mass of atoms / volume of unit cell = 3.51 g/cm3

3.51 g/cm³ = 4.56 x 10-22 g /a3

a3 = 1.299 x 10-22 cm3

a = 5.06 x 10-8 cm

we have a = 4r/√3 for BCC

r = 5.06 x 10-8 cm x √3 / 4 = 2.19 x 10-8 cm

5. Dec 6, 2017

### HAYAO

Why do you need the radius for? Depending on how you are planning to use it, a particular definition of atomic radii may be more suitable for you than the others.

6. Dec 7, 2017

### DrDu

It is hard to understand your question. Are you getting "two" different answers or "too" different answers and from where are you getting answers? What methods are you using? Who is "all"?

7. Dec 7, 2017

### Bobs

All my teachers had found anohter answer for this question (1.34pm, 1.35pm and 1.36pm). And yes, there are too many different answers. I'm checking If that's wrong or not. However, it seems correct. Now let's look at textbook solution, it says that the answer is 1.36pm.