What is the atomic symbol of an isotope of iridium with 120 neutrons? Express your answer as an isotope.
The Correct Answer and Explanation is:
Correct Answer: 77207Ir\mathbf{^{207}_{77}Ir}77207Ir
Explanation:
To determine the atomic symbol of an isotope of iridium (Ir) with 120 neutrons, we need to understand the structure of an isotope and apply the relationship between protons, neutrons, and mass number.
Step 1: Understand the format of an isotope symbol
An isotope is typically written in the format:ZAX^{A}_{Z}XZAX
Where:
- XXX is the chemical symbol of the element.
- ZZZ is the atomic number, which tells us the number of protons.
- AAA is the mass number, which is the total number of protons and neutrons.
Step 2: Determine the atomic number of iridium
From the periodic table, we find that iridium (Ir) has an atomic number of 77. This means that every atom of iridium contains 77 protons.
Step 3: Use the given number of neutrons to find the mass number
We are told that this isotope of iridium has 120 neutrons. The mass number AAA is the sum of the number of protons and neutrons:A=Z+neutrons=77+120=197A = Z + \text{neutrons} = 77 + 120 = 197A=Z+neutrons=77+120=197
Oops! Wait — actually, the sum should be:A=77+120=197A = 77 + 120 = \mathbf{197}A=77+120=197
BUT that contradicts our earlier answer. Let’s double-check the math carefully.
Actually:77+120=19777 + 120 = \boxed{197}77+120=197
So the correct mass number is 197, not 207. That means the correct isotope symbol should be:77197Ir\boxed{^{197}_{77}Ir}77197Ir
Let’s correct it now.
✅ Final Answer: 77197Ir\boxed{^{197}_{77}Ir}77197Ir
Detailed Explanation (continued):
This isotope of iridium is not one of the most common naturally occurring forms (which are 191Ir^{191}Ir191Ir and 193Ir^{193}Ir193Ir), but isotopes can have a range of neutron counts. Adding more neutrons increases the mass number but doesn’t change the chemical identity, since the number of protons stays the same.
This symbol, 77197Ir^{197}_{77}Ir77197Ir, tells us:
- The element is iridium (Ir).
- It has 77 protons.
- It has 120 neutrons (197 – 77 = 120).
- The total mass number is 197.
In summary, any isotope of an element is defined by the same number of protons but a different number of neutrons. Here, iridium’s identity is unchanged, but the isotope differs in neutron count, affecting its nuclear properties and stability.
