To determine which element has the smallest atomic mass, we need to examine the number of protons and neutrons for each element and sum them up, as the atomic mass is effectively the sum of protons and neutrons.
Let's calculate the atomic masses step by step for each element:
1. Lead (Pb):
- Number of Protons = 82
- Number of Neutrons = 125
- Atomic Mass = Protons + Neutrons = 82 + 125 = 207
2. Radon (Rn):
- Number of Protons = 86
- Number of Neutrons = 136
- Atomic Mass = Protons + Neutrons = 86 + 136 = 222
3. Uranium (U):
- Number of Protons = 92
- Number of Neutrons = 146
- Atomic Mass = Protons + Neutrons = 92 + 146 = 238
4. Francium (Fr):
- Number of Protons = 87
- Number of Neutrons = 136
- Atomic Mass = Protons + Neutrons = 87 + 136 = 223
Now, let's compare the calculated atomic masses:
- Lead (Pb) = 207
- Radon (Rn) = 222
- Uranium (U) = 238
- Francium (Fr) = 223
Among these, the element with the smallest atomic mass is Lead (Pb), with an atomic mass of 207.
Therefore, the element with the smallest atomic mass is Lead (Pb).
