Question

How many neutrons does an atom of lithium contain?

Answer 1

Why are noble gases the least reactive elements?
They have a full valence electron shell
They are most electronegative elements
They have an empty inner electron shell
They are the element with the smallest atomic mass

Answer 2

Lithium has an atomic number of 3, which means it has 3 protons. The most common isotope of lithium, lithium-7, has a mass number of 7. The number of neutrons in an atom can be found by subtracting the number of protons from the mass number.

For lithium-7:

Number of neutrons = Mass number - Number of protons = 7 - 3 = 4

Therefore, an atom of lithium-7 contains 4 neutrons. There is also a less common isotope, lithium-6, which has 3 neutrons.

Answer 3

Noble gases are the least reactive elements primarily because **they have a full valence electron shell**.

This full outer shell configuration makes them stable and less likely to gain, lose, or share electrons in chemical reactions, which is why they are known for their lack of reactivity compared to other elements. The other options you provided do not accurately explain the inertness of noble gases:

- **They are most electronegative elements**: This is not true; noble gases have very low electronegativity because they do not readily attract electrons.
- **They have an empty inner electron shell**: This is misleading; noble gases do have inner electron shells, but their outermost shell is full.
- **They are the element with the smallest atomic mass**: This is incorrect; noble gases include the heaviest elements in the group (like radon), and atomic mass does not directly relate to reactivity.

Thus, the correct reason for the low reactivity of noble gases is primarily that they have a full valence electron shell.