| Atomic symbol | Atomic Number | Protons | Neutrons | Electrons | Atomic mass |

Question

|---------------|---------------|---------|----------|-----------|-------------|
| __ | 81 | __ | __ | __ | 206 |

Answer 1

To fill in the missing information for the element with atomic number 81, we can refer to the periodic table. The element with atomic number 81 is Thallium (Tl).

Here’s the completed table:

| Atomic symbol | Atomic Number | Protons | Neutrons | Electrons | Atomic mass | |---------------|---------------|---------|----------|-----------|-------------| | Tl | 81 | 81 | 125 | 81 | 206 |

Notes:

• Protons = Atomic number = 81
• Electrons for a neutral atom are also 81.
• Neutrons can be calculated using the formula: Neutrons = Atomic mass - Protons. Here, Neutrons = 206 - 81 = 125.
• The atomic mass given is the weighted average of the atomic mass of the naturally occurring isotopes of thallium.